Metadata-Version: 1.0
Name: zope.component
Version: 3.7.1
Summary: Zope Component Architecture
Home-page: http://pypi.python.org/pypi/zope.component
Author: Zope Corporation and Contributors
Author-email: zope-dev@zope.org
License: ZPL 2.1
Description: *****************************
        zope.component Package Readme
        *****************************
        
        *This package is intended to be independently reusable in any Python
        project. It is maintained by the* `Zope Toolkit project <http://docs.zope.org/zopetoolkit/>`_.
        
        This package represents the core of the Zope Component Architecture.
        Together with the 'zope.interface' package, it provides facilities for
        defining, registering and looking up components.
        
        .. contents::
        
        Detailed Documentation
        **********************
        
        Zope Component Architecture
        ===========================
        
        This package, together with `zope.interface`, provides facilities for
        defining, registering and looking up components.  There are two basic
        kinds of components: adapters and utilities.
        
        Utilities
        ---------
        
        Utilities are just components that provide an interface and that are
        looked up by an interface and a name.  Let's look at a trivial utility
        definition:
        
        >>> from zope import interface
        
        >>> class IGreeter(interface.Interface):
        ...     def greet():
        ...         "say hello"
        
        >>> class Greeter:
        ...     interface.implements(IGreeter)
        ...
        ...     def __init__(self, other="world"):
        ...         self.other = other
        ...
        ...     def greet(self):
        ...         print "Hello", self.other
        
        We can register an instance this class using `provideUtility` [1]_:
        
        >>> from zope import component
        >>> greet = Greeter('bob')
        >>> component.provideUtility(greet, IGreeter, 'robert')
        
        In this example we registered the utility as providing the `IGreeter`
        interface with a name of 'bob'. We can look the interface up with
        either `queryUtility` or `getUtility`:
        
        >>> component.queryUtility(IGreeter, 'robert').greet()
        Hello bob
        
        >>> component.getUtility(IGreeter, 'robert').greet()
        Hello bob
        
        `queryUtility` and `getUtility` differ in how failed lookups are handled:
        
        >>> component.queryUtility(IGreeter, 'ted')
        >>> component.queryUtility(IGreeter, 'ted', 42)
        42
        >>> component.getUtility(IGreeter, 'ted')
        ... # doctest: +ELLIPSIS
        Traceback (most recent call last):
        ...
        ComponentLookupError: (<InterfaceClass ...IGreeter>, 'ted')
        
        If a component provides only one interface, as in the example above,
        then we can omit the provided interface from the call to `provideUtility`:
        
        >>> ted = Greeter('ted')
        >>> component.provideUtility(ted, name='ted')
        >>> component.queryUtility(IGreeter, 'ted').greet()
        Hello ted
        
        The name defaults to an empty string:
        
        >>> world = Greeter()
        >>> component.provideUtility(world)
        >>> component.queryUtility(IGreeter).greet()
        Hello world
        
        Adapters
        --------
        
        Adapters are components that are computed from other components to
        adapt them to some interface.  Because they are computed from other
        objects, they are provided as factories, usually classes.  Here, we'll
        create a greeter for persons, so we can provide personalized greetings
        for different people:
        
        >>> class IPerson(interface.Interface):
        ...     name = interface.Attribute("Name")
        
        >>> class PersonGreeter:
        ...
        ...     component.adapts(IPerson)
        ...     interface.implements(IGreeter)
        ...
        ...     def __init__(self, person):
        ...         self.person = person
        ...
        ...     def greet(self):
        ...         print "Hello", self.person.name
        
        The class defines a constructor that takes an argument for every
        object adapted.
        
        We used `component.adapts` to declare what we adapt.  We can find
        out if an object declares that it adapts anything using adaptedBy:
        
        >>> list(component.adaptedBy(PersonGreeter)) == [IPerson]
        True
        
        If an object makes no declaration, then None is returned:
        
        >>> component.adaptedBy(Greeter()) is None
        True
        
        
        If we declare the interfaces adapted and if we provide only one
        interface, as in the example above, then we can provide the adapter
        very simply [1]_:
        
        >>> component.provideAdapter(PersonGreeter)
        
        For adapters that adapt a single interface to a single interface
        without a name, we can get the adapter by simply calling the
        interface:
        
        >>> class Person:
        ...     interface.implements(IPerson)
        ...
        ...     def __init__(self, name):
        ...         self.name = name
        
        >>> IGreeter(Person("Sally")).greet()
        Hello Sally
        
        We can also provide arguments to be very specific about what
        how to register the adapter.
        
        >>> class BobPersonGreeter(PersonGreeter):
        ...     name = 'Bob'
        ...     def greet(self):
        ...         print "Hello", self.person.name, "my name is", self.name
        
        >>> component.provideAdapter(
        ...                        BobPersonGreeter, [IPerson], IGreeter, 'bob')
        
        The arguments can also be provided as keyword arguments:
        
        >>> class TedPersonGreeter(BobPersonGreeter):
        ...     name = "Ted"
        
        >>> component.provideAdapter(
        ...     factory=TedPersonGreeter, adapts=[IPerson],
        ...     provides=IGreeter, name='ted')
        
        For named adapters, use `queryAdapter`, or `getAdapter`:
        
        >>> component.queryAdapter(Person("Sally"), IGreeter, 'bob').greet()
        Hello Sally my name is Bob
        
        >>> component.getAdapter(Person("Sally"), IGreeter, 'ted').greet()
        Hello Sally my name is Ted
        
        If an adapter can't be found, `queryAdapter` returns a default value
        and `getAdapter` raises an error:
        
        >>> component.queryAdapter(Person("Sally"), IGreeter, 'frank')
        >>> component.queryAdapter(Person("Sally"), IGreeter, 'frank', 42)
        42
        >>> component.getAdapter(Person("Sally"), IGreeter, 'frank')
        ... # doctest: +ELLIPSIS
        Traceback (most recent call last):
        ...
        ComponentLookupError: (...Person...>, <...IGreeter>, 'frank')
        
        Adapters can adapt multiple objects:
        
        >>> class TwoPersonGreeter:
        ...
        ...     component.adapts(IPerson, IPerson)
        ...     interface.implements(IGreeter)
        ...
        ...     def __init__(self, person, greeter):
        ...         self.person = person
        ...         self.greeter = greeter
        ...
        ...     def greet(self):
        ...         print "Hello", self.person.name
        ...         print "my name is", self.greeter.name
        
        >>> component.provideAdapter(TwoPersonGreeter)
        
        To look up a multi-adapter, use either `queryMultiAdapter` or
        `getMultiAdapter`:
        
        >>> component.queryMultiAdapter((Person("Sally"), Person("Bob")),
        ...                                  IGreeter).greet()
        Hello Sally
        my name is Bob
        
        Adapters need not be classes.  Any callable will do.  We use the
        adapter decorator (in the Python 2.4 decorator sense) to declare that
        a callable object adapts some interfaces (or classes):
        
        >>> class IJob(interface.Interface):
        ...     "A job"
        
        >>> class Job:
        ...     interface.implements(IJob)
        
        >>> def personJob(person):
        ...     return getattr(person, 'job', None)
        >>> personJob = interface.implementer(IJob)(personJob)
        >>> personJob = component.adapter(IPerson)(personJob)
        
        In Python 2.4, the example can be written:
        
        >>> @interface.implementer(IJob)
        ... @component.adapter(IPerson)
        ... def personJob(person):
        ...     return getattr(person, 'job', None)
        
        which looks a bit nicer.
        
        In this example, the personJob function simply returns the person's
        `job` attribute if present, or None if it's not present.  An adapter
        factory can return None to indicate that adaptation wasn't possible.
        Let's register this adapter and try it out:
        
        >>> component.provideAdapter(personJob)
        >>> sally = Person("Sally")
        >>> IJob(sally) # doctest: +ELLIPSIS
        Traceback (most recent call last):
        ...
        TypeError: ('Could not adapt', ...
        
        The adaptation failed because sally didn't have a job.  Let's give her
        one:
        
        >>> job = Job()
        >>> sally.job = job
        >>> IJob(sally) is job
        True
        
        Subscription Adapters
        ---------------------
        
        Unlike regular adapters, subscription adapters are used when we want
        all of the adapters that adapt an object to a particular adapter.
        
        Consider a validation problem.  We have objects and we want to assess
        whether they meet some sort of standards.  We define a validation
        interface:
        
        >>> class IValidate(interface.Interface):
        ...     def validate(ob):
        ...         """Determine whether the object is valid
        ...
        ...         Return a string describing a validation problem.
        ...         An empty string is returned to indicate that the
        ...         object is valid.
        ...         """
        
        Perhaps we have documents:
        
        >>> class IDocument(interface.Interface):
        ...     summary = interface.Attribute("Document summary")
        ...     body = interface.Attribute("Document text")
        
        >>> class Document:
        ...     interface.implements(IDocument)
        ...     def __init__(self, summary, body):
        ...         self.summary, self.body = summary, body
        
        Now, we may want to specify various validation rules for
        documents. For example, we might require that the summary be a single
        line:
        
        >>> class SingleLineSummary:
        ...     component.adapts(IDocument)
        ...     interface.implements(IValidate)
        ...
        ...     def __init__(self, doc):
        ...         self.doc = doc
        ...
        ...     def validate(self):
        ...         if '\n' in self.doc.summary:
        ...             return 'Summary should only have one line'
        ...         else:
        ...             return ''
        
        Or we might require the body to be at least 1000 characters in length:
        
        >>> class AdequateLength:
        ...     component.adapts(IDocument)
        ...     interface.implements(IValidate)
        ...
        ...     def __init__(self, doc):
        ...         self.doc = doc
        ...
        ...     def validate(self):
        ...         if len(self.doc.body) < 1000:
        ...             return 'too short'
        ...         else:
        ...             return ''
        
        We can register these as subscription adapters [1]_:
        
        >>> component.provideSubscriptionAdapter(SingleLineSummary)
        >>> component.provideSubscriptionAdapter(AdequateLength)
        
        We can then use the subscribers to validate objects:
        
        >>> doc = Document("A\nDocument", "blah")
        >>> [adapter.validate()
        ...  for adapter in component.subscribers([doc], IValidate)
        ...  if adapter.validate()]
        ['Summary should only have one line', 'too short']
        
        >>> doc = Document("A\nDocument", "blah" * 1000)
        >>> [adapter.validate()
        ...  for adapter in component.subscribers([doc], IValidate)
        ...  if adapter.validate()]
        ['Summary should only have one line']
        
        >>> doc = Document("A Document", "blah")
        >>> [adapter.validate()
        ...  for adapter in component.subscribers([doc], IValidate)
        ...  if adapter.validate()]
        ['too short']
        
        Handlers
        --------
        
        Handlers are subscription adapter factories that don't produce
        anything.  They do all of their work when called.  Handlers
        are typically used to handle events.
        
        Event subscribers are different from other subscription adapters in
        that the caller of event subscribers doesn't expect to interact with
        them in any direct way.  For example, an event publisher doesn't
        expect to get any return value.  Because subscribers don't need to
        provide an API to their callers, it is more natural to define them
        with functions, rather than classes.  For example, in a
        document-management system, we might want to record creation times for
        documents:
        
        >>> import datetime
        
        >>> def documentCreated(event):
        ...     event.doc.created = datetime.datetime.utcnow()
        
        In this example, we have a function that takes an event and performs
        some processing.  It doesn't actually return anything.  This is a
        special case of a subscription adapter that adapts an event to
        nothing.  All of the work is done when the adapter "factory" is
        called.  We call subscribers that don't actually create anything
        "handlers".  There are special APIs for registering and calling
        them.
        
        To register the subscriber above, we define a document-created event:
        
        >>> class IDocumentCreated(interface.Interface):
        ...     doc = interface.Attribute("The document that was created")
        
        >>> class DocumentCreated:
        ...     interface.implements(IDocumentCreated)
        ...
        ...     def __init__(self, doc):
        ...         self.doc = doc
        
        We'll also change our handler definition to:
        
        >>> def documentCreated(event):
        ...     event.doc.created = datetime.datetime.utcnow()
        
        >>> documentCreated = component.adapter(IDocumentCreated)(documentCreated)
        
        Note that in Python 2.4, this can be written:
        
        >>> @component.adapter(IDocumentCreated)
        ... def documentCreated(event):
        ...     event.doc.created = datetime.datetime.utcnow()
        
        This marks the handler as an adapter of `IDocumentCreated` events.
        
        Now we'll register the handler  [1]_:
        
        >>> component.provideHandler(documentCreated)
        
        Now, if we can create an event and use the `handle` function to call
        handlers registered for the event:
        
        >>> component.handle(DocumentCreated(doc))
        >>> doc.created.__class__.__name__
        'datetime'
        
        
        
        .. [1] CAUTION: This API should only be used from test or
        application-setup code. This API shouldn't be used by regular
        library modules, as component registration is a configuration
        activity.
        
        Events
        ======
        
        The Component Architecture provides a way to dispatch events to event
        handlers.  Event handlers are registered as *subscribers*
        a.k.a. *handlers*.
        
        Before we can start we need to import ``zope.component.event`` to make
        the dispatching effective:
        
        >>> import zope.component.event
        
        Consider two event classes:
        
        >>> class Event1(object):
        ...     pass
        
        >>> class Event2(Event1):
        ...     pass
        
        Now consider two handlers for these event classes:
        
        >>> called = []
        
        >>> import zope.component
        >>> @zope.component.adapter(Event1)
        ... def handler1(event):
        ...     called.append(1)
        
        >>> @zope.component.adapter(Event2)
        ... def handler2(event):
        ...     called.append(2)
        
        We can register them with the Component Architecture:
        
        >>> zope.component.provideHandler(handler1)
        >>> zope.component.provideHandler(handler2)
        
        Now let's go through the events.  We'll see that the handlers have been
        called accordingly:
        
        >>> from zope.event import notify
        >>> notify(Event1())
        >>> called
        [1]
        
        >>> del called[:]
        >>> notify(Event2())
        >>> called.sort()
        >>> called
        [1, 2]
        
        
        
        Object events
        -------------
        
        
        The ``objectEventNotify`` function is a subscriber to dispatch
        ObjectEvents to interested adapters.
        
        First create an object class:
        
        >>> class IUseless(zope.interface.Interface):
        ...     """Useless object"""
        
        >>> class UselessObject(object):
        ...     """Useless object"""
        ...     zope.interface.implements(IUseless)
        
        Then create an event class:
        
        >>> class IObjectThrownEvent(zope.component.interfaces.IObjectEvent):
        ...     """An object has been thrown away"""
        
        >>> class ObjectThrownEvent(zope.component.interfaces.ObjectEvent):
        ...     """An object has been thrown away"""
        ...     zope.interface.implements(IObjectThrownEvent)
        
        Create an object and an event:
        
        >>> hammer = UselessObject()
        >>> event = ObjectThrownEvent(hammer)
        
        Then notify the event to the subscribers.
        Since the subscribers list is empty, nothing happens.
        
        >>> zope.component.event.objectEventNotify(event)
        
        Now create an handler for the event:
        
        >>> events = []
        >>> def record(*args):
        ...     events.append(args)
        
        >>> zope.component.provideHandler(record, [IUseless, IObjectThrownEvent])
        
        The event is notified to the subscriber:
        
        >>> zope.component.event.objectEventNotify(event)
        >>> events == [(hammer, event)]
        True
        
        Following test demonstrates how a subscriber can raise an exception
        to prevent an action.
        
        >>> zope.component.provideHandler(zope.component.event.objectEventNotify)
        
        Let's create a container:
        
        >>> class ToolBox(dict):
        ...     def __delitem__(self, key):
        ...         notify(ObjectThrownEvent(self[key]))
        ...         return super(ToolBox,self).__delitem__(key)
        
        >>> container = ToolBox()
        
        And put the object into the container:
        
        >>> container['Red Hammer'] = hammer
        
        Create an handler function that will raise an error when called:
        
        >>> class Veto(Exception):
        ...     pass
        
        >>> def callback(item, event):
        ...     assert(item == event.object)
        ...     raise Veto
        
        Register the handler:
        
        >>> zope.component.provideHandler(callback, [IUseless, IObjectThrownEvent])
        
        Then if we try to remove the object, an ObjectThrownEvent is fired:
        
        >>> del container['Red Hammer']
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        raise Veto
        Veto
        
        Factories
        =========
        
        
        The Factory Class
        -----------------
        
        >>> from zope.interface import Interface
        >>> class IFunction(Interface):
        ...     pass
        
        >>> class IKlass(Interface):
        ...     pass
        
        >>> from zope.interface import implements
        >>> class Klass(object):
        ...     implements(IKlass)
        ...
        ...     def __init__(self, *args, **kw):
        ...         self.args = args
        ...         self.kw = kw
        
        >>> from zope.component.factory import Factory
        >>> factory = Factory(Klass, 'Klass', 'Klassier')
        >>> factory2 = Factory(lambda x: x, 'Func', 'Function')
        >>> factory3 = Factory(lambda x: x, 'Func', 'Function', (IFunction,))
        
        Calling a Factory
        ~~~~~~~~~~~~~~~~~
        
        Here we test whether the factory correctly creates the objects and
        including the correct handling of constructor elements.
        
        First we create a factory that creates instanace of the `Klass` class:
        
        >>> factory = Factory(Klass, 'Klass', 'Klassier')
        
        Now we use the factory to create the instance
        
        >>> kl = factory(1, 2, foo=3, bar=4)
        
        and make sure that the correct class was used to create the object:
        
        >>> kl.__class__
        <class 'Klass'>
        
        Since we passed in a couple positional and keyword arguments
        
        >>> kl.args
        (1, 2)
        >>> kl.kw
        {'foo': 3, 'bar': 4}
        
        >>> factory2(3)
        3
        >>> factory3(3)
        3
        
        
        Title and Description
        ~~~~~~~~~~~~~~~~~~~~~
        
        >>> factory.title
        'Klass'
        >>> factory.description
        'Klassier'
        >>> factory2.title
        'Func'
        >>> factory2.description
        'Function'
        >>> factory3.title
        'Func'
        >>> factory3.description
        'Function'
        
        
        Provided Interfaces
        ~~~~~~~~~~~~~~~~~~~
        
        >>> implemented = factory.getInterfaces()
        >>> implemented.isOrExtends(IKlass)
        True
        >>> list(implemented)
        [<InterfaceClass __builtin__.IKlass>]
        
        >>> implemented2 = factory2.getInterfaces()
        >>> list(implemented2)
        []
        
        >>> implemented3 = factory3.getInterfaces()
        >>> list(implemented3)
        [<InterfaceClass __builtin__.IFunction>]
        
        
        The Component Architecture Factory API
        --------------------------------------
        
        >>> import zope.component
        >>> factory = Factory(Klass, 'Klass', 'Klassier')
        >>> gsm = zope.component.getGlobalSiteManager()
        
        >>> from zope.component.interfaces import IFactory
        >>> gsm.registerUtility(factory, IFactory, 'klass')
        
        Creating an Object
        ~~~~~~~~~~~~~~~~~~
        
        >>> kl = zope.component.createObject('klass', 1, 2, foo=3, bar=4)
        >>> isinstance(kl, Klass)
        True
        >>> kl.args
        (1, 2)
        >>> kl.kw
        {'foo': 3, 'bar': 4}
        
        Accessing Provided Interfaces
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        
        >>> implemented = zope.component.getFactoryInterfaces('klass')
        >>> implemented.isOrExtends(IKlass)
        True
        >>> [iface for iface in implemented]
        [<InterfaceClass __builtin__.IKlass>]
        
        List of All Factories
        ~~~~~~~~~~~~~~~~~~~~~
        
        >>> [(name, fac.__class__) for name, fac in
        ...  zope.component.getFactoriesFor(IKlass)]
        [(u'klass', <class 'zope.component.factory.Factory'>)]
        
        
        Component-Management objects
        ============================
        
        Component-management objects provide a higher-level
        component-management API over the basic adapter-registration API
        provided by the zope.interface package.  In particular, it provides:
        
        - utilities
        
        - support for computing adapters, rather than just looking up adapter
        factories.
        
        - management of registration comments
        
        The zope.component.registry.Components class provides an
        implementation of zope.component.interfaces.IComponents that provides
        these features.
        
        >>> from zope.component import registry
        >>> from zope.component import tests
        >>> components = registry.Components('comps')
        
        As components are registered, events are generated.  Let's register
        an event subscriber, so we can see the events generated:
        
        >>> import zope.event
        >>> def logevent(event):
        ...     print event
        >>> zope.event.subscribers.append(logevent)
        
        Utilities
        ---------
        
        You can register Utilities using registerUtility:
        
        >>> components.registerUtility(tests.U1(1))
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 1, None, u'')
        
        Here we didn't specify an interface or name.  An unnamed utility was
        registered for interface I1, since that is only interface implemented
        by the U1 class:
        
        >>> components.getUtility(tests.I1)
        U1(1)
        
        You can also register a utility using a factory instead of a utility instance:
        
        >>> def factory():
        ...    return tests.U1(1)
        >>> components.registerUtility(factory=factory)
        Unregistered event:
        UtilityRegistration(<Components comps>, I1, u'', 1, None, u'')
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 1, <function factory at <SOME ADDRESS>>, u'')
        
        
        If a component implements other than one interface or no interface,
        then an error will be raised:
        
        >>> components.registerUtility(tests.U12(2))
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The utility doesn't provide a single interface and
        no provided interface was specified.
        
        >>> components.registerUtility(tests.A)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The utility doesn't provide a single interface and
        no provided interface was specified.
        
        
        We can provide an interface if desired:
        
        >>> components.registerUtility(tests.U12(2), tests.I2)
        Registered event:
        UtilityRegistration(<Components comps>, I2, u'', 2, None, u'')
        
        and we can specify a name:
        
        >>> components.registerUtility(tests.U12(3), tests.I2, u'three')
        Registered event:
        UtilityRegistration(<Components comps>, I2, u'three', 3, None, u'')
        
        >>> components.getUtility(tests.I2)
        U12(2)
        
        >>> components.getUtility(tests.I2, 'three')
        U12(3)
        
        If you try to get a utility that doesn't exist, you'll get a component
        lookup error:
        
        >>> components.getUtility(tests.I3)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        ComponentLookupError:
        (<InterfaceClass zope.component.tests.I3>, u'')
        
        Unless you use queryUtility:
        
        >>> components.queryUtility(tests.I3)
        >>> components.queryUtility(tests.I3, default=42)
        42
        
        You can get information about registered utilities with the
        registeredUtilities method:
        
        >>> for registration in sorted(components.registeredUtilities()):
        ...     print registration.provided, registration.name
        ...     print registration.component, registration.info
        <InterfaceClass zope.component.tests.I1>
        U1(1)
        <InterfaceClass zope.component.tests.I2>
        U12(2)
        <InterfaceClass zope.component.tests.I2> three
        U12(3)
        
        Duplicate registrations replace existing ones:
        
        >>> components.registerUtility(tests.U1(4), info=u'use 4 now')
        Unregistered event:
        UtilityRegistration(<Components comps>, I1, u'', 1, <function factory at <SOME ADDRESS>>, u'')
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 4, None, u'use 4 now')
        >>> components.getUtility(tests.I1)
        U1(4)
        
        >>> for registration in sorted(components.registeredUtilities()):
        ...     print registration.provided, registration.name
        ...     print registration.component, registration.info
        <InterfaceClass zope.component.tests.I1>
        U1(4) use 4 now
        <InterfaceClass zope.component.tests.I2>
        U12(2)
        <InterfaceClass zope.component.tests.I2> three
        U12(3)
        
        As shown in the this example, you can provide an "info" argumemnt when
        registering utilities.  This provides extra documentation about the
        registration itself that is shown when listing registrations.
        
        You can also unregister utilities:
        
        >>> components.unregisterUtility(provided=tests.I1)
        Unregistered event:
        UtilityRegistration(<Components comps>, I1, u'', 4, None, u'use 4 now')
        True
        
        A boolean is returned indicating whether anything changed:
        
        >>> components.queryUtility(tests.I1)
        >>> for registration in sorted(components.registeredUtilities()):
        ...     print registration.provided, registration.name
        ...     print registration.component, registration.info
        <InterfaceClass zope.component.tests.I2>
        U12(2)
        <InterfaceClass zope.component.tests.I2> three
        U12(3)
        
        When you unregister, you can specify a component.  If the component
        doesn't match the one registered, then nothing happens:
        
        >>> u5 = tests.U1(5)
        >>> components.registerUtility(u5)
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
        >>> components.unregisterUtility(tests.U1(6))
        False
        >>> components.queryUtility(tests.I1)
        U1(5)
        >>> components.unregisterUtility(u5)
        Unregistered event:
        UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
        True
        >>> components.queryUtility(tests.I1)
        
        You can get the name and utility for all of the utilities that provide
        an interface using getUtilitiesFor:
        
        >>> sorted(components.getUtilitiesFor(tests.I2))
        [(u'', U12(2)), (u'three', U12(3))]
        
        getAllUtilitiesRegisteredFor is similar to getUtilitiesFor except that
        it includes utilities that are overridden.  For example, we'll
        register a utility that for an extending interface of I2:
        
        >>> util = tests.U('ext')
        >>> components.registerUtility(util, tests.I2e)
        Registered event:
        UtilityRegistration(<Components comps>, I2e, u'', ext, None, u'')
        
        We don't get the new utility for getUtilitiesFor:
        
        >>> sorted(components.getUtilitiesFor(tests.I2))
        [(u'', U12(2)), (u'three', U12(3))]
        
        but we do get it from getAllUtilitiesRegisteredFor:
        
        >>> sorted(map(str, components.getAllUtilitiesRegisteredFor(tests.I2)))
        ['U(ext)', 'U12(2)', 'U12(3)']
        
        Removing a utility also makes it disappear from getUtilitiesFor:
        
        >>> components.unregisterUtility(util, tests.I2e)
        Unregistered event:
        UtilityRegistration(<Components comps>, I2e, u'', ext, None, u'')
        True
        >>> list(components.getAllUtilitiesRegisteredFor(tests.I2e))
        []
        
        Adapters
        --------
        
        You can register adapters with registerAdapter:
        
        >>> components.registerAdapter(tests.A12_1)
        Registered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
        
        Here, we didn't specify required interfaces, a provided interface, or
        a name.  The required interfaces were determined from the factory
        s __component_adapts__ attribute and the provided interface was
        determined by introspecting what the factory implements.
        
        >>> components.getMultiAdapter((tests.U1(6), tests.U12(7)), tests.IA1)
        A12_1(U1(6), U12(7))
        
        If a factory implements more than one interface, an exception will be
        raised:
        
        >>> components.registerAdapter(tests.A1_12)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single
        interface and no provided interface was specified.
        
        Unless the provided interface is specified:
        
        >>> components.registerAdapter(tests.A1_12, provided=tests.IA2)
        Registered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
        
        If a factory doesn't declare an implemented interface, an exception will be
        raised:
        
        >>> components.registerAdapter(tests.A12_)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single
        interface and no provided interface was specified.
        
        Unless the provided interface is specified:
        
        >>> components.registerAdapter(tests.A12_, provided=tests.IA2)
        Registered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA2, u'', A12_, u'')
        
        The required interface needs to be specified in the registration if
        the factory doesn't have a __component_adapts__ attribute:
        
        >>> components.registerAdapter(tests.A_2)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't have a __component_adapts__
        attribute and no required specifications were specified
        
        Unless the required specifications specified:
        
        >>> components.registerAdapter(tests.A_2, required=[tests.I3])
        Registered event:
        AdapterRegistration(<Components comps>, [I3], IA2, u'', A_2, u'')
        
        Classes can be specified in place of specifications, in which case the
        implementedBy specification for the class is used:
        
        >>> components.registerAdapter(tests.A_3, required=[tests.U],
        ...                            info="Really class specific")
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        AdapterRegistration(<Components comps>, [zope.component.tests.U], IA3, u'',
        A_3, 'Really class specific')
        
        We can see the adapters that have been registered using the
        registeredAdapters method:
        
        >>> for registration in sorted(components.registeredAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        ... # doctest: +NORMALIZE_WHITESPACE
        (<InterfaceClass zope.component.tests.I1>,
        <InterfaceClass zope.component.tests.I2>)
        <InterfaceClass zope.component.tests.IA1>
        zope.component.tests.A12_1
        (<InterfaceClass zope.component.tests.I1>,
        <InterfaceClass zope.component.tests.I2>)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A12_
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A1_12
        (<InterfaceClass zope.component.tests.I3>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A_2
        (<implementedBy zope.component.tests.U>,)
        <InterfaceClass zope.component.tests.IA3>
        zope.component.tests.A_3 Really class specific
        
        As with utilities, we can provide registration information when
        registering adapters.
        
        If you try to fetch an adapter that isn't registered, you'll get a
        component-lookup error:
        
        >>> components.getMultiAdapter((tests.U(8), ), tests.IA1)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        ComponentLookupError: ((U(8),),
        <InterfaceClass zope.component.tests.IA1>, u'')
        
        unless you use queryAdapter:
        
        >>> components.queryMultiAdapter((tests.U(8), ), tests.IA1)
        >>> components.queryMultiAdapter((tests.U(8), ), tests.IA1, default=42)
        42
        
        When looking up an adapter for a single object, you can use the
        slightly simpler getAdapter and queryAdapter calls:
        
        >>> components.getAdapter(tests.U1(9), tests.IA2)
        A1_12(U1(9))
        
        >>> components.queryAdapter(tests.U1(9), tests.IA2)
        A1_12(U1(9))
        
        >>> components.getAdapter(tests.U(8), tests.IA1)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        ComponentLookupError: (U(8),
        <InterfaceClass zope.component.tests.IA1>, u'')
        
        >>> components.queryAdapter(tests.U(8), tests.IA2)
        >>> components.queryAdapter(tests.U(8), tests.IA2, default=42)
        42
        
        You can unregister an adapter.  If a factory is provided and if the
        rewuired and provided interfaces, can be infered, then they need not
        be provided:
        
        >>> components.unregisterAdapter(tests.A12_1)
        Unregistered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
        True
        
        >>> for registration in sorted(components.registeredAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        ... # doctest: +NORMALIZE_WHITESPACE
        (<InterfaceClass zope.component.tests.I1>,
        <InterfaceClass zope.component.tests.I2>)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A12_
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A1_12
        (<InterfaceClass zope.component.tests.I3>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A_2
        (<implementedBy zope.component.tests.U>,)
        <InterfaceClass zope.component.tests.IA3>
        zope.component.tests.A_3 Really class specific
        
        A boolean is returned indicating whether a change was made.
        
        If a factory implements more than one interface, an exception will be
        raised:
        
        >>> components.unregisterAdapter(tests.A1_12)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single
        interface and no provided interface was specified.
        
        Unless the provided interface is specified:
        
        >>> components.unregisterAdapter(tests.A1_12, provided=tests.IA2)
        Unregistered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
        True
        
        If a factory doesn't declare an implemented interface, an exception will be
        raised:
        
        >>> components.unregisterAdapter(tests.A12_)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single
        interface and no provided interface was specified.
        
        Unless the provided interface is specified:
        
        >>> components.unregisterAdapter(tests.A12_, provided=tests.IA2)
        Unregistered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA2, u'', A12_, u'')
        True
        
        The required interface needs to be specified if the factory doesn't
        have a __component_adapts__ attribute:
        
        >>> components.unregisterAdapter(tests.A_2)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't have a __component_adapts__
        attribute and no required specifications were specified
        
        >>> components.unregisterAdapter(tests.A_2, required=[tests.I3])
        Unregistered event:
        AdapterRegistration(<Components comps>, [I3], IA2, u'', A_2, u'')
        True
        
        >>> for registration in sorted(components.registeredAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        ... # doctest: +NORMALIZE_WHITESPACE
        (<implementedBy zope.component.tests.U>,)
        <InterfaceClass zope.component.tests.IA3>
        zope.component.tests.A_3 Really class specific
        
        If a factory is unregistered that is not registered, False is
        returned:
        
        
        >>> components.unregisterAdapter(tests.A_2, required=[tests.I3])
        False
        >>> components.unregisterAdapter(tests.A12_1, required=[tests.U])
        False
        
        The factory can be omitted, to unregister *any* factory that matches
        specified required and provided interfaces:
        
        >>> components.unregisterAdapter(required=[tests.U], provided=tests.IA3)
        ... # doctest: +NORMALIZE_WHITESPACE
        Unregistered event:
        AdapterRegistration(<Components comps>, [zope.component.tests.U],
        IA3, u'', A_3, 'Really class specific')
        True
        
        >>> for registration in sorted(components.registeredAdapters()):
        ...     print registration
        
        Adapters can be named:
        
        >>> components.registerAdapter(tests.A1_12, provided=tests.IA2,
        ...                            name=u'test')
        Registered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'test', A1_12, u'')
        
        >>> components.queryMultiAdapter((tests.U1(9), ), tests.IA2)
        >>> components.queryMultiAdapter((tests.U1(9), ), tests.IA2, name=u'test')
        A1_12(U1(9))
        
        >>> components.queryAdapter(tests.U1(9), tests.IA2)
        >>> components.queryAdapter(tests.U1(9), tests.IA2, name=u'test')
        A1_12(U1(9))
        >>> components.getAdapter(tests.U1(9), tests.IA2, name=u'test')
        A1_12(U1(9))
        
        It is possible to look up all of the adapters that provide an
        interface:
        
        >>> components.registerAdapter(tests.A1_23, provided=tests.IA2,
        ...                            name=u'test 2')
        Registered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'test 2', A1_23, u'')
        
        >>> components.registerAdapter(tests.A1_12, provided=tests.IA2)
        Registered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
        
        >>> for name, adapter in sorted(components.getAdapters((tests.U1(9), ),
        ...                                                    tests.IA2)):
        ...     print name, adapter
        A1_12(U1(9))
        test A1_12(U1(9))
        test 2 A1_23(U1(9))
        
        
        getAdapters is most commonly used as the basis of menu systems.
        
        If an adapter factory returns None, it is equivalent to there being no
        factory:
        
        >>> components.registerAdapter(tests.noop,
        ...                            required=[tests.IA1], provided=tests.IA2,
        ...                            name=u'test noop')
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        AdapterRegistration(<Components comps>, [IA1], IA2, u'test noop',
        noop, u'')
        >>> components.queryAdapter(tests.U1(9), tests.IA2, name=u'test noop')
        
        >>> components.registerAdapter(tests.A1_12, provided=tests.IA2)
        Registered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
        
        >>> for name, adapter in sorted(components.getAdapters((tests.U1(9), ),
        ...                                                    tests.IA2)):
        ...     print name, adapter
        A1_12(U1(9))
        test A1_12(U1(9))
        test 2 A1_23(U1(9))
        
        
        >>> components.unregisterAdapter(tests.A1_12, provided=tests.IA2,
        ...                              name=u'test')
        Unregistered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'test', A1_12, u'')
        True
        >>> components.unregisterAdapter(tests.A1_12, provided=tests.IA2)
        Unregistered event:
        AdapterRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
        True
        >>> for registration in sorted(components.registeredAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        ... # doctest: +NORMALIZE_WHITESPACE
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2> test 2
        zope.component.tests.A1_23
        (<InterfaceClass zope.component.tests.IA1>,)
        <InterfaceClass zope.component.tests.IA2> test noop
        <function noop at 0xb79a1064>
        
        
        Subscribers
        -----------
        
        Subscribers provide a way to get multiple adapters of a given type.
        In this regard, subscribers are like named adapters, except that there
        isn't any concept of the most specific adapter for a given name.
        
        Subscribers are registered by calling registerSubscriptionAdapter:
        
        >>> components.registerSubscriptionAdapter(tests.A1_2)
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
        
        >>> components.registerSubscriptionAdapter(
        ...     tests.A1_12, provided=tests.IA2)
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_12, u'')
        
        >>> components.registerSubscriptionAdapter(
        ...     tests.A, [tests.I1], tests.IA2,
        ...     info='a sample comment')
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'',
        A, 'a sample comment')
        
        The same rules, with regard to when required and provided interfaces
        have to be specified apply as with adapters:
        
        >>> components.registerSubscriptionAdapter(tests.A1_12)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single
        interface and no provided interface was specified.
        
        >>> components.registerSubscriptionAdapter(tests.A)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single interface and
        no provided interface was specified.
        
        >>> components.registerSubscriptionAdapter(tests.A, required=[tests.IA1])
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single interface
        and no provided interface was specified.
        
        Note that we provided the info argument as a keyword argument above.
        That's because there is a name argument that's reserved for future
        use. We can give a name, as long as it is an empty string:
        
        >>> components.registerSubscriptionAdapter(
        ...     tests.A, [tests.I1], tests.IA2, u'', 'a sample comment')
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'',
        A, 'a sample comment')
        
        >>> components.registerSubscriptionAdapter(
        ...     tests.A, [tests.I1], tests.IA2, u'oops', 'a sample comment')
        Traceback (most recent call last):
        ...
        TypeError: Named subscribers are not yet supported
        
        Subscribers are looked up using the subscribers method:
        
        >>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
        ...    print s
        A1_2(U1(1))
        A1_12(U1(1))
        A(U1(1),)
        A(U1(1),)
        
        Note that, because we created multiple subscriptions for A, we got multiple
        subscriber instances.
        
        As with normal adapters, if a factory returns None, the result is skipped:
        
        >>> components.registerSubscriptionAdapter(
        ...     tests.noop, [tests.I1], tests.IA2)
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', noop, u'')
        
        >>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
        ...    print s
        A1_2(U1(1))
        A1_12(U1(1))
        A(U1(1),)
        A(U1(1),)
        
        We can get registration information for subscriptions:
        
        >>> for registration in sorted(
        ...     components.registeredSubscriptionAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A a sample comment
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A a sample comment
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A1_12
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A1_2
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        <function noop at 0xb796ff7c>
        
        We can also unregister subscriptions in much the same way we can for adapters:
        
        >>> components.unregisterSubscriptionAdapter(tests.A1_2)
        ... # doctest: +NORMALIZE_WHITESPACE
        Unregistered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, '')
        True
        
        >>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
        ...    print s
        A1_12(U1(1))
        A(U1(1),)
        A(U1(1),)
        
        >>> for registration in sorted(
        ...     components.registeredSubscriptionAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A a sample comment
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A a sample comment
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A1_12
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        <function noop at 0xb796ff7c>
        
        >>> components.unregisterSubscriptionAdapter(
        ...     tests.A, [tests.I1], tests.IA2)
        Unregistered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A, '')
        True
        
        >>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
        ...    print s
        A1_12(U1(1))
        
        >>> for registration in sorted(
        ...     components.registeredSubscriptionAdapters()):
        ...     print registration.required
        ...     print registration.provided, registration.name
        ...     print registration.factory, registration.info
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        zope.component.tests.A1_12
        (<InterfaceClass zope.component.tests.I1>,)
        <InterfaceClass zope.component.tests.IA2>
        <function noop at 0xb796ff7c>
        
        Note here that both registrations for A were removed.
        
        If we omit the factory, we must specify the required and provided interfaces:
        
        >>> components.unregisterSubscriptionAdapter(required=[tests.I1])
        Traceback (most recent call last):
        ...
        TypeError: Must specify one of factory and provided
        
        >>> components.unregisterSubscriptionAdapter(provided=tests.IA2)
        Traceback (most recent call last):
        ...
        TypeError: Must specify one of factory and required
        
        >>> components.unregisterSubscriptionAdapter(
        ...     required=[tests.I1], provided=tests.IA2)
        Unregistered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', None, '')
        True
        
        >>> for s in components.subscribers((tests.U1(1), ), tests.IA2):
        ...    print s
        
        >>> for registration in sorted(
        ...     components.registeredSubscriptionAdapters()):
        ...     print registration.factory
        
        As when registering, an error is raised if the registration
        information can't be determined from the factory and isn't specified:
        
        >>> components.unregisterSubscriptionAdapter(tests.A1_12)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single
        interface and no provided interface was specified.
        
        >>> components.unregisterSubscriptionAdapter(tests.A)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single interface and
        no provided interface was specified.
        
        >>> components.unregisterSubscriptionAdapter(tests.A, required=[tests.IA1])
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't implement a single interface
        and no provided interface was specified.
        
        If you unregister something that's not registered, nothing will be
        changed and False will be returned:
        
        
        >>> components.unregisterSubscriptionAdapter(
        ...     required=[tests.I1], provided=tests.IA2)
        False
        
        Handlers
        --------
        
        Handlers are used when you want to perform some function in response
        to an event.  Handlers aren't expected to return anything when called
        and are not registered to provide any interface.
        
        >>> from zope import component
        >>> @component.adapter(tests.I1)
        ... def handle1(x):
        ...     print 'handle1', x
        
        >>> components.registerHandler(handle1, info="First handler")
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        HandlerRegistration(<Components comps>, [I1], u'',
        handle1, 'First handler')
        >>> components.handle(tests.U1(1))
        handle1 U1(1)
        
        >>> @component.adapter(tests.I1, tests.I2)
        ... def handle12(x, y):
        ...     print 'handle12', x, y
        
        >>> components.registerHandler(handle12)
        Registered event:
        HandlerRegistration(<Components comps>, [I1, I2], u'', handle12, u'')
        >>> components.handle(tests.U1(1), tests.U12(2))
        handle12 U1(1) U12(2)
        
        If a handler doesn't document interfaces it handles, then
        the required interfaces must be specified:
        
        >>> def handle(*objects):
        ...     print 'handle', objects
        
        >>> components.registerHandler(handle)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't have a __component_adapts__
        attribute and no required specifications were specified
        
        >>> components.registerHandler(handle, required=[tests.I1],
        ...                            info="a comment")
        Registered event:
        HandlerRegistration(<Components comps>, [I1], u'', handle, 'a comment')
        
        Handlers can also be registered for classes:
        
        >>> components.registerHandler(handle, required=[tests.U],
        ...                            info="handle a class")
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        HandlerRegistration(<Components comps>, [zope.component.tests.U], u'',
        handle, 'handle a class')
        
        
        >>> components.handle(tests.U1(1))
        handle (U1(1),)
        handle1 U1(1)
        handle (U1(1),)
        
        We can list the handler registrations:
        
        >>> for registration in components.registeredHandlers():
        ...     print registration.required
        ...     print registration.handler, registration.info
        ... # doctest: +NORMALIZE_WHITESPACE
        (<InterfaceClass zope.component.tests.I1>,)
        <function handle1 at 0xb78f5bfc> First handler
        (<InterfaceClass zope.component.tests.I1>,
        <InterfaceClass zope.component.tests.I2>)
        <function handle12 at 0xb78f5c34>
        (<InterfaceClass zope.component.tests.I1>,)
        <function handle at 0xb78f5ca4> a comment
        (<implementedBy zope.component.tests.U>,)
        <function handle at 0xb78f5ca4> handle a class
        
        and we can unregister handlers:
        
        >>> components.unregisterHandler(required=[tests.U])
        ... # doctest: +NORMALIZE_WHITESPACE
        Unregistered event:
        HandlerRegistration(<Components comps>, [zope.component.tests.U], u'',
        None, '')
        True
        
        >>> for registration in components.registeredHandlers():
        ...     print registration.required
        ...     print registration.handler, registration.info
        ... # doctest: +NORMALIZE_WHITESPACE
        (<InterfaceClass zope.component.tests.I1>,)
        <function handle1 at 0xb78f5bfc> First handler
        (<InterfaceClass zope.component.tests.I1>,
        <InterfaceClass zope.component.tests.I2>)
        <function handle12 at 0xb78f5c34>
        (<InterfaceClass zope.component.tests.I1>,)
        <function handle at 0xb78f5ca4> a comment
        
        >>> components.unregisterHandler(handle12)
        Unregistered event:
        HandlerRegistration(<Components comps>, [I1, I2], u'', handle12, '')
        True
        
        >>> for registration in components.registeredHandlers():
        ...     print registration.required
        ...     print registration.handler, registration.info
        (<InterfaceClass zope.component.tests.I1>,)
        <function handle1 at 0xb78f5bfc> First handler
        (<InterfaceClass zope.component.tests.I1>,)
        <function handle at 0xb78f5ca4> a comment
        
        >>> components.unregisterHandler(handle12)
        False
        
        >>> components.unregisterHandler()
        Traceback (most recent call last):
        ...
        TypeError: Must specify one of factory and required
        
        >>> components.registerHandler(handle)
        ... # doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        TypeError: The adapter factory doesn't have a __component_adapts__
        attribute and no required specifications were specified
        
        Extending
        ---------
        
        Component-management objects can extend other component-management
        objects.
        
        >>> c1 = registry.Components('1')
        >>> c1.__bases__
        ()
        
        >>> c2 = registry.Components('2', (c1, ))
        >>> c2.__bases__ == (c1, )
        True
        
        >>> c1.registerUtility(tests.U1(1))
        Registered event:
        UtilityRegistration(<Components 1>, I1, u'', 1, None, u'')
        
        >>> c1.queryUtility(tests.I1)
        U1(1)
        >>> c2.queryUtility(tests.I1)
        U1(1)
        >>> c1.registerUtility(tests.U1(2))
        Unregistered event:
        UtilityRegistration(<Components 1>, I1, u'', 1, None, u'')
        Registered event:
        UtilityRegistration(<Components 1>, I1, u'', 2, None, u'')
        
        >>> c2.queryUtility(tests.I1)
        U1(2)
        
        We can use multiple inheritence:
        
        >>> c3 = registry.Components('3', (c1, ))
        >>> c4 = registry.Components('4', (c2, c3))
        >>> c4.queryUtility(tests.I1)
        U1(2)
        
        >>> c1.registerUtility(tests.U12(1), tests.I2)
        Registered event:
        UtilityRegistration(<Components 1>, I2, u'', 1, None, u'')
        
        >>> c4.queryUtility(tests.I2)
        U12(1)
        
        >>> c3.registerUtility(tests.U12(3), tests.I2)
        Registered event:
        UtilityRegistration(<Components 3>, I2, u'', 3, None, u'')
        >>> c4.queryUtility(tests.I2)
        U12(3)
        
        >>> c1.registerHandler(handle1, info="First handler")
        Registered event:
        HandlerRegistration(<Components 1>, [I1], u'', handle1, 'First handler')
        
        >>> c2.registerHandler(handle, required=[tests.U])
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        HandlerRegistration(<Components 2>, [zope.component.tests.U], u'',
        handle, u'')
        
        >>> @component.adapter(tests.I1)
        ... def handle3(x):
        ...     print 'handle3', x
        >>> c3.registerHandler(handle3)
        Registered event:
        HandlerRegistration(<Components 3>, [I1], u'', handle3, u'')
        
        >>> @component.adapter(tests.I1)
        ... def handle4(x):
        ...     print 'handle4', x
        >>> c4.registerHandler(handle4)
        Registered event:
        HandlerRegistration(<Components 4>, [I1], u'', handle4, u'')
        
        >>> c4.handle(tests.U1(1))
        handle1 U1(1)
        handle3 U1(1)
        handle (U1(1),)
        handle4 U1(1)
        
        Redispatch of registration events
        ---------------------------------
        
        Some handlers are available that, if registered, redispatch
        registration events to the objects being registered.  They depend on
        being dispatched to by the object-event dispatcher:
        
        >>> from zope import component
        >>> import zope.component.event
        >>> zope.component.getGlobalSiteManager().registerHandler(
        ...      zope.component.event.objectEventNotify)
        ... # doctest: +NORMALIZE_WHITESPACE
        Registered event:
        HandlerRegistration(<BaseGlobalComponents base>,
        [IObjectEvent], u'', objectEventNotify, u'')
        
        To see this, we'll first register a multi-handler to show is when
        handlers are called on 2 objects:
        
        >>> @zope.component.adapter(None, None)
        ... def double_handler(o1, o2):
        ...     print 'Double dispatch:'
        ...     print ' ', o1
        ...     print ' ', o2
        >>> zope.component.getGlobalSiteManager().registerHandler(double_handler)
        ... # doctest: +NORMALIZE_WHITESPACE
        Double dispatch:
        HandlerRegistration(<BaseGlobalComponents base>,
        [Interface, Interface], u'', double_handler, u'')
        Registered event:
        HandlerRegistration(<BaseGlobalComponents base>,
        [Interface, Interface], u'', double_handler, u'')
        Registered event:
        HandlerRegistration(<BaseGlobalComponents base>,
        [Interface, Interface], u'', double_handler, u'')
        
        In the example above, the double_handler reported it's own registration. :)
        
        Now we'll register our handlers:
        
        >>> zope.component.getGlobalSiteManager().registerHandler(
        ...     registry.dispatchUtilityRegistrationEvent)
        ... # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
        Double dispatch:
        ...
        
        >>> zope.component.getGlobalSiteManager().registerHandler(
        ...     registry.dispatchAdapterRegistrationEvent)
        ... # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
        Double dispatch:
        ...
        
        >>> zope.component.getGlobalSiteManager().registerHandler(
        ...     registry.dispatchSubscriptionAdapterRegistrationEvent)
        ... # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
        Double dispatch:
        ...
        
        >>> zope.component.getGlobalSiteManager().registerHandler(
        ...     registry.dispatchHandlerRegistrationEvent)
        ... # doctest: +NORMALIZE_WHITESPACE
        Double dispatch:
        HandlerRegistration(<BaseGlobalComponents base>,
        [IHandlerRegistration, IRegistrationEvent], u'',
        dispatchHandlerRegistrationEvent, u'')
        Registered event:
        HandlerRegistration(<BaseGlobalComponents base>,
        [IHandlerRegistration, IRegistrationEvent], u'',
        dispatchHandlerRegistrationEvent, u'')
        Double dispatch:
        <function dispatchHandlerRegistrationEvent at 0xb799f72c>
        Registered event:
        HandlerRegistration(<BaseGlobalComponents base>,
        [IHandlerRegistration, IRegistrationEvent], u'',
        dispatchHandlerRegistrationEvent, u'')
        Registered event:
        HandlerRegistration(<BaseGlobalComponents base>,
        [IHandlerRegistration, IRegistrationEvent], u'',
        dispatchHandlerRegistrationEvent, u'')
        
        In the last example above, we can see that the registration of
        dispatchHandlerRegistrationEvent was handled by
        dispatchHandlerRegistrationEvent and redispatched.  This can be seen
        in the second double-dispatch output, where the first argument is the
        object being registered, which is dispatchHandlerRegistrationEvent.
        
        If we change some other registrations, we can the double dispatch
        taking place:
        
        >>> components.registerUtility(u5)
        ... # doctest: +NORMALIZE_WHITESPACE
        Double dispatch:
        UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
        Double dispatch:
        U1(5)
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
        Registered event:
        UtilityRegistration(<Components comps>, I1, u'', 5, None, u'')
        
        >>> components.registerAdapter(tests.A12_1)
        ... # doctest: +NORMALIZE_WHITESPACE
        Double dispatch:
        AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
        Registered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
        Double dispatch:
        zope.component.tests.A12_1
        Registered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
        Registered event:
        AdapterRegistration(<Components comps>, [I1, I2], IA1, u'', A12_1, u'')
        
        >>> components.registerSubscriptionAdapter(tests.A1_2)
        ... # doctest: +NORMALIZE_WHITESPACE
        Double dispatch:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
        Double dispatch:
        zope.component.tests.A1_2
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
        Registered event:
        SubscriptionRegistration(<Components comps>, [I1], IA2, u'', A1_2, u'')
        
        Persistent Component Management
        ===============================
        
        Persistent component management allows persistent management of
        components.  From a usage point of view, there shouldn't be any new
        behavior beyond what's described in registry.txt.
        
        The Zope 3 Component Architecture (Socket Example)
        ==================================================
        
        The component architecture provides an application framework that provides its
        functionality through loosely-connected components. A *component* can be any
        Python object and has a particular purpose associated with it. Thus, in a
        component-based applications you have many small component in contrast to
        classical object-oriented development, where you have a few big objects.
        
        Components communicate via specific APIs, which are formally defined by
        interfaces, which are provided by the `zope.interface` package. *Interfaces*
        describe the methods and properties that a component is expected to
        provide. They are also used as a primary mean to provide developer-level
        documentation for the components. For more details about interfaces see
        `zope/interface/README.txt`.
        
        The two main types of components are *adapters* and *utilities*. They will be
        discussed in detail later in this document. Both component types are managed
        by the *site manager*, with which you can register and access these
        components. However, most of the site manager's functionality is hidden behind
        the component architecture's public API, which is documented in
        `IComponentArchitecture`.
        
        
        Adapters
        --------
        
        Adapters are a well-established pattern. An *adapter* uses an object providing
        one interface to produce an object that provides another interface. Here an
        example: Imagine that you purchased an electric shaver in the US, and thus
        you require the US socket type. You are now traveling in Germany, where another
        socket style is used. You will need a device, an adapter, that converts from
        the German to the US socket style.
        
        The functionality of adapters is actually natively provided by the
        `zope.interface` package and is thus well documented there. The `human.txt`
        file provides a gentle introduction to adapters, whereby `adapter.txt` is
        aimed at providing a comprehensive insight into adapters, but is too abstract
        for many as an initial read. Thus, we will only explain adapters in the context
        of the component architecture's API.
        
        So let's say that we have a German socket
        
        >>> from zope.interface import Interface, implements
        
        >>> class IGermanSocket(Interface):
        ...     pass
        
        >>> class Socket(object):
        ...     def __repr__(self):
        ...         return '<instance of %s>' %self.__class__.__name__
        
        >>> class GermanSocket(Socket):
        ...     """German wall socket."""
        ...     implements(IGermanSocket)
        
        and we want to convert it to an US socket
        
        >>> class IUSSocket(Interface):
        ...     pass
        
        so that our shaver can be used in Germany. So we go to a German electronics
        store to look for an adapter that we can plug in the wall:
        
        >>> class GermanToUSSocketAdapter(Socket):
        ...     implements(IUSSocket)
        ...     __used_for__ = IGermanSocket
        ...
        ...     def __init__(self, socket):
        ...         self.context = socket
        
        Note that I could have called the passed in socket any way I like, but
        `context` is the standard name accepted.
        
        
        Single Adapters
        ~~~~~~~~~~~~~~~
        
        Before we can use the adapter, we have to buy it and make it part of our
        inventory. In the component architecture we do this by registering the adapter
        with the framework, more specifically with the global site manager:
        
        >>> import zope.component
        >>> gsm = zope.component.getGlobalSiteManager()
        >>> gsm.registerAdapter(GermanToUSSocketAdapter, (IGermanSocket,), IUSSocket)
        
        `zope.component` is the component architecture API that is being
        presented by this file. You registered an adapter from `IGermanSocket`
        to `IUSSocket` having no name (thus the empty string).
        
        Anyways, you finally get back to your hotel room and shave, since you have not
        been able to shave in the plane. In the bathroom you discover a socket:
        
        >>> bathroomDE = GermanSocket()
        >>> IGermanSocket.providedBy(bathroomDE)
        True
        
        You now insert the adapter in the German socket
        
        >>> bathroomUS = zope.component.getAdapter(bathroomDE, IUSSocket, '')
        
        so that the socket now provides the US version:
        
        >>> IUSSocket.providedBy(bathroomUS)
        True
        
        Now you can insert your shaver and get on with your day.
        
        After a week you travel for a couple of days to the Prague and you notice that
        the Czech have yet another socket type:
        
        >>> class ICzechSocket(Interface):
        ...     pass
        
        >>> class CzechSocket(Socket):
        ...     implements(ICzechSocket)
        
        >>> czech = CzechSocket()
        
        You try to find an adapter for your shaver in your bag, but you fail, since
        you do not have one:
        
        >>> zope.component.getAdapter(czech, IUSSocket, '') \
        ... #doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        ComponentLookupError: (<instance of CzechSocket>,
        <InterfaceClass __builtin__.IUSSocket>,
        '')
        
        or the more graceful way:
        
        >>> marker = object()
        >>> socket = zope.component.queryAdapter(czech, IUSSocket, '', marker)
        >>> socket is marker
        True
        
        In the component architecture API any `get*` method will fail with a specific
        exception, if a query failed, whereby methods starting with `query*` will
        always return a `default` value after a failure.
        
        
        Named Adapters
        ~~~~~~~~~~~~~~
        
        You are finally back in Germany. You also brought your DVD player and a couple
        DVDs with you, which you would like to watch. Your shaver was able to convert
        automatically from 110 volts to 240 volts, but your DVD player cannot. So you
        have to buy another adapter that also handles converting the voltage and the
        frequency of the AC current:
        
        >>> class GermanToUSSocketAdapterAndTransformer(object):
        ...     implements(IUSSocket)
        ...     __used_for__ = IGermanSocket
        ...
        ...     def __init__(self, socket):
        ...         self.context = socket
        
        Now, we need a way to keep the two adapters apart. Thus we register them with
        a name:
        
        >>> gsm.registerAdapter(GermanToUSSocketAdapter,
        ...                     (IGermanSocket,), IUSSocket, 'shaver',)
        >>> gsm.registerAdapter(GermanToUSSocketAdapterAndTransformer,
        ...                     (IGermanSocket,), IUSSocket, 'dvd')
        
        Now we simply look up the adapters using their labels (called *name*):
        
        >>> socket = zope.component.getAdapter(bathroomDE, IUSSocket, 'shaver')
        >>> socket.__class__ is GermanToUSSocketAdapter
        True
        
        >>> socket = zope.component.getAdapter(bathroomDE, IUSSocket, 'dvd')
        >>> socket.__class__ is GermanToUSSocketAdapterAndTransformer
        True
        
        Clearly, we do not have an adapter for the MP3 player
        
        >>> zope.component.getAdapter(bathroomDE, IUSSocket, 'mp3') \
        ... #doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        ComponentLookupError: (<instance of GermanSocket>,
        <InterfaceClass __builtin__.IUSSocket>,
        'mp3')
        
        but you could use the 'dvd' adapter in this case of course. ;)
        
        Sometimes you want to know all adapters that are available. Let's say you want
        to know about all the adapters that convert a German to a US socket type:
        
        >>> sockets = list(zope.component.getAdapters((bathroomDE,), IUSSocket))
        >>> len(sockets)
        3
        >>> names = [name for name, socket in sockets]
        >>> names.sort()
        >>> names
        [u'', u'dvd', u'shaver']
        
        `zope.component.getAdapters()` returns a list of tuples. The first
        entry of the tuple is the name of the adapter and the second is the
        adapter itself.
        
        
        Multi-Adapters
        ~~~~~~~~~~~~~~
        
        After watching all the DVDs you brought at least twice, you get tired of them
        and you want to listen to some music using your MP3 player. But darn, the MP3
        player plug has a ground pin and all the adapters you have do not support
        that:
        
        >>> class IUSGroundedSocket(IUSSocket):
        ...     pass
        
        So you go out another time to buy an adapter. This time, however, you do not
        buy yet another adapter, but a piece that provides the grounding plug:
        
        >>> class IGrounder(Interface):
        ...     pass
        
        >>> class Grounder(object):
        ...     implements(IGrounder)
        ...     def __repr__(self):
        ...         return '<instance of Grounder>'
        
        
        Then together they will provided a grounded us socket:
        
        >>> class GroundedGermanToUSSocketAdapter(object):
        ...     implements(IUSGroundedSocket)
        ...     __used_for__ = (IGermanSocket, IGrounder)
        ...     def __init__(self, socket, grounder):
        ...         self.socket, self.grounder = socket, grounder
        
        You now register the combination, so that you know you can create a
        `IUSGroundedSocket`:
        
        >>> gsm.registerAdapter(GroundedGermanToUSSocketAdapter,
        ...                 (IGermanSocket, IGrounder), IUSGroundedSocket, 'mp3')
        
        Given the grounder
        
        >>> grounder = Grounder()
        
        and a German socket
        
        >>> livingroom = GermanSocket()
        
        we can now get a grounded US socket:
        
        >>> socket = zope.component.getMultiAdapter((livingroom, grounder),
        ...                                         IUSGroundedSocket, 'mp3')
        
        >>> socket.__class__ is GroundedGermanToUSSocketAdapter
        True
        >>> socket.socket is livingroom
        True
        >>> socket.grounder is grounder
        True
        
        Of course, you do not have a 'dvd' grounded US socket available:
        
        >>> zope.component.getMultiAdapter((livingroom, grounder),
        ...                                IUSGroundedSocket, 'dvd') \
        ... #doctest: +NORMALIZE_WHITESPACE
        Traceback (most recent call last):
        ...
        ComponentLookupError: ((<instance of GermanSocket>,
        <instance of Grounder>),
        <InterfaceClass __builtin__.IUSGroundedSocket>,
        'dvd')
        
        
        >>> socket = zope.component.queryMultiAdapter(
        ...     (livingroom, grounder), IUSGroundedSocket, 'dvd', marker)
        >>> socket is marker
        True
        
        Again, you might want to read `adapter.txt` in `zope.interface` for a more
        comprehensive coverage of multi-adapters.
        
        Subscribers
        -----------
        
        While subscribers are directly supported by the adapter registry and are
        adapters for all theoretical purposes, practically it might be better to think
        of them as separate components. Subscribers are particularly useful for
        events.
        
        Let's say one of our adapters overheated and caused a small fire:
        
        >>> class IFire(Interface):
        ...     pass
        
        >>> class Fire(object):
        ...     implements(IFire)
        
        >>> fire = Fire()
        
        We want to use all available objects to put out the fire:
        
        >>> class IFireExtinguisher(Interface):
        ...     def extinguish():
        ...         pass
        
        >>> class FireExtinguisher(object):
        ...     def __init__(self, fire):
        ...         pass
        ...     def extinguish(self):
        ...         "Place extinguish code here."
        ...         print 'Used ' + self.__class__.__name__ + '.'
        
        Here some specific methods to put out the fire:
        
        >>> class PowderExtinguisher(FireExtinguisher):
        ...     pass
        >>> gsm.registerSubscriptionAdapter(PowderExtinguisher,
        ...                                 (IFire,), IFireExtinguisher)
        
        >>> class Blanket(FireExtinguisher):
        ...     pass
        >>> gsm.registerSubscriptionAdapter(Blanket, (IFire,), IFireExtinguisher)
        
        >>> class SprinklerSystem(FireExtinguisher):
        ...     pass
        >>> gsm.registerSubscriptionAdapter(SprinklerSystem,
        ...                                 (IFire,), IFireExtinguisher)
        
        Now let use all these things to put out the fire:
        
        >>> extinguishers = zope.component.subscribers((fire,), IFireExtinguisher)
        >>> extinguishers.sort()
        >>> for extinguisher in extinguishers:
        ...     extinguisher.extinguish()
        Used Blanket.
        Used PowderExtinguisher.
        Used SprinklerSystem.
        
        If no subscribers are found for a particular object, then an empty list is
        returned:
        
        >>> zope.component.subscribers((object(),), IFireExtinguisher)
        []
        
        
        Utilities
        ---------
        
        Utilities are the second type of component, the component architecture
        implements. *Utilities* are simply components that provide an interface. When
        you register an utility, you always register an instance (in contrast to a
        factory for adapters) since the initialization and setup process of a utility
        might be complex and is not well defined. In some ways a utility is much more
        fundamental than an adapter, because an adapter cannot be used without another
        component, but a utility is always self-contained. I like to think of
        utilities as the foundation of your application and adapters as components
        extending beyond this foundation.
        
        Back to our story...
        
        After your vacation is over you fly back home to Tampa, Florida. But it is
        August now, the middle of the Hurricane season. And, believe it or not, you are
        worried that you will not be able to shave when the power goes out for several
        days. (You just hate wet shavers.)
        
        So you decide to go to your favorite hardware store and by a Diesel-powered
        electric generator. The generator provides of course a US-style socket:
        
        >>> class Generator(object):
        ...     implements(IUSSocket)
        ...     def __repr__(self):
        ...         return '<instance of Generator>'
        
        >>> generator = Generator()
        
        Like for adapters, we now have to add the newly-acquired generator to our
        inventory by registering it as a utility:
        
        >>> gsm.registerUtility(generator, IUSSocket)
        
        We can now get the utility using
        
        >>> utility = zope.component.getUtility(IUSSocket)
        >>> utility is generator
        True
        
        As you can see, it is very simple to register and retrieve utilities. If a
        utility does not exist for a particular interface, such as the German socket,
        then the lookup fails
        
        >>> zope.component.getUtility(IGermanSocket)
        Traceback (most recent call last):
        ...
        ComponentLookupError: (<InterfaceClass __builtin__.IGermanSocket>, '')
        
        or more gracefully when specifying a default value:
        
        >>> default = object()
        >>> utility = zope.component.queryUtility(IGermanSocket, default=default)
        >>> utility is default
        True
        
        Note: The only difference between `getUtility()` and `queryUtility()` is the
        fact that you can specify a default value for the latter function, so that it
        will never cause a `ComponentLookupError`.
        
        
        Named Utilities
        ~~~~~~~~~~~~~~~
        
        It is often desirable to have several utilities providing the same interface
        per site. This way you can implement any sort of registry using utilities. For
        this reason, utilities -- like adapters -- can be named.
        
        In the context of our story, we might want to do the following: You really do
        not trust gas stations either. What if the roads are blocked after a hurricane
        and the gas stations run out of oil. So you look for another renewable power
        source. Then you think about solar panels! After a storm there is usually very
        nice weather, so why not? Via the Web you order a set of 110V/120W solar
        panels that provide a regular US-style socket as output:
        
        >>> class SolarPanel(object):
        ...     implements(IUSSocket)
        ...     def __repr__(self):
        ...         return '<instance of Solar Panel>'
        
        >>> panel = SolarPanel()
        
        Once it arrives, we add it to our inventory:
        
        >>> gsm.registerUtility(panel, IUSSocket, 'Solar Panel')
        
        You can now access the solar panel using
        
        >>> utility = zope.component.getUtility(IUSSocket, 'Solar Panel')
        >>> utility is panel
        True
        
        Of course, if a utility is not available, then the lookup will simply fail
        
        >>> zope.component.getUtility(IUSSocket, 'Wind Mill')
        Traceback (most recent call last):
        ...
        ComponentLookupError: (<InterfaceClass __builtin__.IUSSocket>, 'Wind Mill')
        
        or more gracefully when specifying a default value:
        
        >>> default = object()
        >>> utility = zope.component.queryUtility(IUSSocket, 'Wind Mill',
        ...                                       default=default)
        >>> utility is default
        True
        
        Now you want to look at all the utilities you have for a particular kind. The
        following API function will return a list of name/utility pairs:
        
        >>> utils = list(zope.component.getUtilitiesFor(IUSSocket))
        >>> utils.sort()
        >>> utils #doctest: +NORMALIZE_WHITESPACE
        [(u'', <instance of Generator>),
        (u'Solar Panel', <instance of Solar Panel>)]
        
        Another method of looking up all utilities is by using
        `getAllUtilitiesRegisteredFor(iface)`. This function will return an iterable
        of utilities (without names); however, it will also return overridden
        utilities. If you are not using multiple site managers, you will not actually
        need this method.
        
        >>> utils = list(zope.component.getAllUtilitiesRegisteredFor(IUSSocket))
        >>> utils.sort()
        >>> utils
        [<instance of Generator>, <instance of Solar Panel>]
        
        
        Factories
        ~~~~~~~~~
        
        A *factory* is a special kind of utility that exists to create other
        components. A factory is always identified by a name. It also provides a title
        and description and is able to tell the developer what interfaces the created
        object will provide. The advantage of using a factory to create an object
        instead of directly instantiating a class or executing any other callable is
        that we can refer to the factory by name. As long as the name stays fixed, the
        implementation of the callable can be renamed or moved without a breakage in
        code.
        
        Let's say that our solar panel comes in parts and they have to be
        assembled. This assembly would be done by a factory, so let's create one for
        the solar panel. To do this, we can use a standard implementation of the
        `IFactory` interface:
        
        >>> from zope.component.factory import Factory
        >>> factory = Factory(SolarPanel,
        ...                   'Solar Panel',
        ...                   'This factory creates a solar panel.')
        
        Optionally, I could have also specified the interfaces that the created object
        will provide, but the factory class is smart enough to determine the
        implemented interface from the class. We now register the factory:
        
        >>> from zope.component.interfaces import IFactory
        >>> gsm.registerUtility(factory, IFactory, 'SolarPanel')
        
        We can now get a list of interfaces the produced object will provide:
        
        >>> ifaces = zope.component.getFactoryInterfaces('SolarPanel')
        >>> IUSSocket in ifaces
        True
        
        By the way, this is equivalent to
        
        >>> ifaces2 = factory.getInterfaces()
        >>> ifaces is ifaces2
        True
        
        Of course you can also just create an object:
        
        >>> panel = zope.component.createObject('SolarPanel')
        >>> panel.__class__ is SolarPanel
        True
        
        Note: Ignore the first argument (`None`) for now; it is the context of the
        utility lookup, which is usually an optional argument, but cannot be in this
        case, since all other arguments beside the `name` are passed in as arguments
        to the specified callable.
        
        Once you register several factories
        
        >>> gsm.registerUtility(Factory(Generator), IFactory, 'Generator')
        
        you can also determine, which available factories will create objects
        providing a certain interface:
        
        >>> factories = zope.component.getFactoriesFor(IUSSocket)
        >>> factories = [(name, factory.__class__) for name, factory in factories]
        >>> factories.sort()
        >>> factories #doctest: +NORMALIZE_WHITESPACE
        [(u'Generator', <class 'zope.component.factory.Factory'>),
        (u'SolarPanel', <class 'zope.component.factory.Factory'>)]
        
        
        Site Managers
        -------------
        
        Why do we need site managers? Why is the component architecture API not
        sufficient? Some applications, including Zope 3, have a concept of
        locations. It is often desirable to have different configurations for these
        location; this can be done by overwriting existing or adding new component
        registrations. Site managers in locations below the root location, should be
        able to delegate requests to their parent locations. The root site manager is
        commonly known as *global site manager*, since it is always available. You can
        always get the global site manager using the API:
        
        >>> gsm = zope.component.getGlobalSiteManager()
        
        >>> from zope.component import globalSiteManager
        >>> gsm is globalSiteManager
        True
        >>> from zope.component.interfaces import IComponentLookup
        >>> IComponentLookup.providedBy(gsm)
        True
        >>> from zope.component.interfaces import IComponents
        >>> IComponents.providedBy(gsm)
        True
        
        You can also lookup at site manager in a given context. The only requirement
        is that the context can be adapted to a site manager. So let's create a
        special site manager:
        
        >>> from zope.component.globalregistry import BaseGlobalComponents
        >>> sm = BaseGlobalComponents()
        
        Now we create a context that adapts to the site manager via the `__conform__`
        method as specified in PEP 246.
        
        >>> class Context(object):
        ...     def __init__(self, sm):
        ...         self.sm = sm
        ...     def __conform__(self, interface):
        ...         if interface.isOrExtends(IComponentLookup):
        ...             return self.sm
        
        We now instantiate the `Context` with our special site manager:
        
        >>> context = Context(sm)
        >>> context.sm is sm
        True
        
        We can now ask for the site manager of this context:
        
        >>> lsm = zope.component.getSiteManager(context)
        >>> lsm is sm
        True
        
        The site manager instance `lsm` is formally known as a *local site manager* of
        `context`.
        
        CHANGES
        *******
        
        3.7.1 (2009-07-24)
        ==================
        
        - Fixed a problem, where ``queryNextUtility`` could fail if the context could
        not be adapted to a ``IComponentLookup``.
        
        - Fixed 2 related bugs:
        
        When a utility is registered and there was previously a utility
        registered for the same interface and name, then the old utility is
        unregistered.  The 2 bugs related to this:
        
        - There was no ``Unregistered`` for the implicit unregistration. Now
        there is.
        
        - The old utility was still held and returned by
        getAllUtilitiesRegisteredFor.  In other words, it was still
        considered registered, eeven though it wasn't.  A particularly
        negative consequence of this is that the utility is held in memory
        or in the database even though it isn't used.
        
        3.7.0 (2009-05-21)
        ==================
        
        - The HookableTests were not run by the testrunner.
        
        - Add in zope:view and zope:resource implementations into
        zope.component.zcml (dependency loaded with zope.component [zcml]).
        
        3.6.0 (2009-03-12)
        ==================
        
        - IMPORTANT: the interfaces that were defined in the
        zope.component.bbb.interfaces and deprecated for years are
        now (re)moved. However, some packages, including part of zope
        framework were still using those interfaces. They will be adapted
        for this change. If you were using some of those interfaces, you
        need to adapt your code as well:
        
        - The IView and IDefaultViewName were moved to zope.publisher.interfaces.
        
        - The IResource was moved to zope.app.publisher.interfaces.
        
        - IContextDependent, IPresentation, IPresentationRequest,
        IResourceFactory, IViewFactory were removed completely.
        
        If you used IViewFactory in context of zope.app.form, there's now
        IWidgetFactory in the zope.app.form.interfaces instead.
        
        - Add getNextUtility/queryNextUtility functions that used to be in zope.site
        earlier (and in zope.app.component even more earlier).
        
        - Added a pure-Python 'hookable' implementation, for use when
        'zope.hookable' is not present.
        
        - Removed use of 'zope.deferredimport' by breaking import cycles.
        
        - Cleanup package documentation and changelog a bit. Add sphinx-based
        documentation building command to the buildout.
        
        - Remove deprecated code.
        
        - Change package's mailing list address to zope-dev at zope.org, because
        zope3-dev at zope.org is now retired.
        
        3.5.1 (2008-07-25)
        ==================
        
        - Fix bug introduced in 3.5.0: <utility factory="..."> no longer supported
        interfaces declared in Python and always wanted an explicit provides="..."
        attribute. https://bugs.launchpad.net/zope3/+bug/251865
        
        3.5.0 (2008-07-25)
        ==================
        
        - Support registration of utilities via factories through the component registry
        and return factory information in the registration information. This fixes
        https://bugs.launchpad.net/zope3/+bug/240631
        
        - Optimized un/registerUtility via storing an optimized data structure for
        efficient retrieval of already registered utilities. This avoids looping over
        all utilities when registering a new one.
        
        3.4.0 (2007-09-29)
        ==================
        
        No further changes since 3.4.0a1.
        
        3.4.0a1 (2007-04-22)
        ====================
        
        Corresponds to zope.component from Zope 3.4.0a1.
        
        - In the Zope 3.3.x series, ``zope.component`` was simplified yet once
        more.  See http://wiki.zope.org/zope3/LocalComponentManagementSimplification
        for the proposal describing the changes.
        
        3.2.0.2 (2006-04-15)
        ====================
        
        - Fix packaging bug:  'package_dir' must be a *relative* path.
        
        3.2.0.1 (2006-04-14)
        ====================
        
        - Packaging change: suppress inclusion of 'setup.cfg' in 'sdist' builds.
        
        3.2.0 (2006-01-05)
        ==================
        
        Corresponds to the verison of the zope.component package shipped as part of
        the Zope 3.2.0 release.
        
        - Deprecated services and related APIs. The adapter and utility registries
        are now available directly via the site manager's 'adapters' and 'utilities'
        attributes, respectively.  Services are accessible, but deprecated, and
        will be removed in Zope 3.3.
        
        - Deprectaed all presentation-related APIs, including all view-related
        API functions. Use the adapter API functions instead.
        See http://dev.zope.org/Zope3/ImplementViewsAsAdapters`
        
        - Deprecated 'contextdependent' package:  site managers are now looked up
        via a thread global, set during URL traversal.  The 'context' argument
        is now always optional, and should no longer be passed.
        
        3.0.0 (2004-11-07)
        ==================
        
        Corresponds to the verison of the zope.component package shipped as part of
        the Zope X3.0.0 release.
        
        Download
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