Metadata-Version: 1.0
Name: zope.schema
Version: 3.5.4
Summary: zope.interface extension for defining data schemas
Home-page: http://pypi.python.org/pypi/zope.schema
Author: Zope Corporation and Contributors
Author-email: zope-dev@zope.org
License: ZPL 2.1
Description: ==============
        Zope 3 Schemas
        ==============
        
        Introduction
        ------------
        
        Schemas extend the notion of interfaces to detailed descriptions of Attributes
        (but not methods). Every schema is an interface and specifies the public
        fields of an object. A *field* roughly corresponds to an attribute of a
        python object. But a Field provides space for at least a title and a
        description. It can also constrain its value and provide a validation method.
        Besides you can optionally specify characteristics such as its value being
        read-only or not required.
        
        Zope 3 schemas were born when Jim Fulton and Martijn Faassen thought
        about Formulator for Zope 3 and ``PropertySets`` while at the `Zope 3
        sprint`_ at the Zope BBQ in Berlin. They realized that if you strip
        all view logic from forms then you have something similar to interfaces. And
        thus schemas were born.
        
        .. _Zope 3 sprint: http://dev.zope.org/Zope3/ZopeBBQ2002Sprint
        
        .. contents::
        
        Simple Usage
        ------------
        
        Let's have a look at a simple example. First we write an interface as usual,
        but instead of describing the attributes of the interface with ``Attribute``
        instances, we now use schema fields:
        
        >>> import zope.interface
        >>> import zope.schema
        
        >>> class IBookmark(zope.interface.Interface):
        ...     title = zope.schema.TextLine(
        ...         title=u'Title',
        ...         description=u'The title of the bookmark',
        ...         required=True)
        ...
        ...     url = zope.schema.URI(
        ...         title=u'Bookmark URL',
        ...         description=u'URL of the Bookmark',
        ...         required=True)
        ...
        
        Now we create a class that implements this interface and create an instance of
        it:
        
        >>> class Bookmark(object):
        ...     zope.interface.implements(IBookmark)
        ...
        ...     title = None
        ...     url = None
        
        >>> bm = Bookmark()
        
        We would now like to only add validated values to the class. This can be done
        by first validating and then setting the value on the object. The first step
        is to define some data:
        
        >>> title = u'Zope 3 Website'
        >>> url = 'http://dev.zope.org/Zope3'
        
        Now we, get the fields from the interface:
        
        >>> title_field = IBookmark.get('title')
        >>> url_field = IBookmark.get('url')
        
        Next we have to bind these fields to the context, so that instance-specific
        information can be used for validation:
        
        >>> title_bound = title_field.bind(bm)
        >>> url_bound = url_field.bind(bm)
        
        Now that the fields are bound, we can finally validate the data:
        
        >>> title_bound.validate(title)
        >>> url_bound.validate(url)
        
        If the validation is successful, ``None`` is returned. If a validation error
        occurs a ``ValidationError`` will be raised; for example:
        
        >>> url_bound.validate(u'http://zope.org/foo')
        Traceback (most recent call last):
        ...
        WrongType: (u'http://zope.org/foo', <type 'str'>)
        
        >>> url_bound.validate('foo.bar')
        Traceback (most recent call last):
        ...
        InvalidURI: foo.bar
        
        Now that the data has been successfully validated, we can set it on the
        object:
        
        >>> title_bound.set(bm, title)
        >>> url_bound.set(bm, url)
        
        That's it. You still might think this is a lot of work to validate and set a
        value for an object. Note, however, that it is very easy to write helper
        functions that automate these tasks. If correctly designed, you will never
        have to worry explicitely about validation again, since the system takes care
        of it automatically.
        
        
        What is a schema, how does it compare to an interface?
        ------------------------------------------------------
        
        A schema is an extended interface which defines fields.  You can validate that
        the attributes of an object conform to their fields defined on the schema.
        With plain interfaces you can only validate that methods conform to their
        interface specification.
        
        So interfaces and schemas refer to different aspects of an object
        (respectively its code and state).
        
        A schema starts out like an interface but defines certain fields to
        which an object's attributes must conform.  Let's look at a stripped
        down example from the programmer's tutorial:
        
        >>> import re
        
        >>> class IContact(zope.interface.Interface):
        ...     """Provides access to basic contact information."""
        ...
        ...     first = zope.schema.TextLine(title=u"First name")
        ...
        ...     last = zope.schema.TextLine(title=u"Last name")
        ...
        ...     email = zope.schema.TextLine(title=u"Electronic mail address")
        ...
        ...     address = zope.schema.Text(title=u"Postal address")
        ...
        ...     postalCode = zope.schema.TextLine(
        ...         title=u"Postal code",
        ...         constraint=re.compile("\d{5,5}(-\d{4,4})?$").match)
        
        ``TextLine`` is a field and expresses that an attribute is a single line
        of Unicode text.  ``Text`` expresses an arbitrary Unicode ("text")
        object.  The most interesting part is the last attribute
        specification.  It constrains the ``postalCode`` attribute to only have
        values that are US postal codes.
        
        Now we want a class that adheres to the ``IContact`` schema:
        
        >>> class Contact(object):
        ...     zope.interface.implements(IContact)
        ...
        ...     def __init__(self, first, last, email, address, pc):
        ...         self.first = first
        ...         self.last = last
        ...         self.email = email
        ...         self.address = address
        ...         self.postalCode = pc
        
        Now you can see if an instance of ``Contact`` actually implements the
        schema:
        
        >>> someone = Contact(u'Tim', u'Roberts', u'tim@roberts', u'',
        ...                   u'12032-3492')
        
        >>> for field in zope.schema.getFields(IContact).values():
        ...     bound = field.bind(someone)
        ...     bound.validate(bound.get(someone))
        
        
        Data Modeling Concepts
        -----------------------
        
        The ``zope.schema`` package provides a core set of field types,
        including single- and multi-line text fields, binary data fields,
        integers, floating-point numbers, and date/time values.
        
        Selection issues; field type can specify:
        
        - "Raw" data value
        
        Simple values not constrained by a selection list.
        
        - Value from enumeration (options provided by schema)
        
        This models a single selection from a list of possible values
        specified by the schema.  The selection list is expected to be the
        same for all values of the type.  Changes to the list are driven by
        schema evolution.
        
        This is done by mixing-in the ``IEnumerated`` interface into the field
        type, and the Enumerated mix-in for the implementation (or emulating
        it in a concrete class).
        
        - Value from selection list (options provided by an object)
        
        This models a single selection from a list of possible values
        specified by a source outside the schema.  The selection list
        depends entirely on the source of the list, and may vary over time
        and from object to object.  Changes to the list are not related to
        the schema, but changing how the list is determined is based on
        schema evolution.
        
        There is not currently a spelling of this, but it could be
        facilitated using alternate mix-ins similar to IEnumerated and
        Enumerated.
        
        - Whether or not the field is read-only
        
        If a field value is read-only, it cannot be changed once the object is
        created.
        
        - Whether or not the field is required
        
        If a field is designated as required, assigned field values must always
        be non-missing. See the next section for a description of missing values.
        
        - A value designated as ``missing``
        
        Missing values, when assigned to an object, indicate that there is 'no
        data' for that field. Missing values are analogous to null values in
        relational databases. For example, a boolean value can be True, False, or
        missing, in which case its value is unknown.
        
        While Python's None is the most likely value to signify 'missing', some
        fields may use different values. For example, it is common for text fields
        to use the empty string ('') to signify that a value is missing. Numeric
        fields may use 0 or -1 instead of None as their missing value.
        
        A field that is 'required' signifies that missing values are invalid and
        should not be assigned.
        
        - A default value
        
        Default field values are assigned to objects when they are first created.
        
        
        Fields and Widgets
        ------------------
        
        Widgets are components that display field values and, in the case of
        writable fields, allow the user to edit those values.
        
        Widgets:
        
        - Display current field values, either in a read-only format, or in a
        format that lets the user change the field value.
        
        - Update their corresponding field values based on values provided by users.
        
        - Manage the relationships between their representation of a field value
        and the object's field value. For example, a widget responsible for
        editing a number will likely represent that number internally as a string.
        For this reason, widgets must be able to convert between the two value
        formats. In the case of the number-editing widget, string values typed
        by the user need to be converted to numbers such as int or float.
        
        - Support the ability to assign a missing value to a field. For example,
        a widget may present a ``None`` option for selection that, when selected,
        indicates that the object should be updated with the field's ``missing``
        value.
        
        
        
        References
        ----------
        
        - Use case list, http://dev.zope.org/Zope3/Zope3SchemasUseCases
        
        - Documented interfaces, zope/schema/interfaces.py
        
        - Jim Fulton's Programmers Tutorial; in CVS:
        Docs/ZopeComponentArchitecture/PythonProgrammerTutorial/Chapter2
        
        
        ======
        Fields
        ======
        
        This document highlights unusual and subtle aspects of various fields and
        field classes, and is not intended to be a general introduction to schema
        fields.  Please see README.txt for a more general introduction.
        
        While many field types, such as Int, TextLine, Text, and Bool are relatively
        straightforward, a few have some subtlety.  We will explore the general
        class of collections and discuss how to create a custom creation field; discuss
        Choice fields, vocabularies, and their use with collections; and close with a
        look at the standard zope.app approach to using these fields to find views
        ("widgets").
        
        Collections
        -----------
        
        Normal fields typically describe the API of the attribute -- does it behave as a
        Python Int, or a Float, or a Bool -- and various constraints to the model, such
        as a maximum or minimum value.  Collection fields have additional requirements
        because they contain other types, which may also be described and constrained.
        
        For instance, imagine a list that contains non-negative floats and enforces
        uniqueness. In a schema, this might be written as follows:
        
        >>> from zope.interface import Interface
        >>> from zope.schema import List, Float
        >>> class IInventoryItem(Interface):
        ...     pricePoints = List(
        ...         title=u"Price Points",
        ...         unique=True,
        ...         value_type=Float(title=u"Price", min=0.0)
        ...     )
        
        This indicates several things.
        
        - pricePoints is an attribute of objects that implement IInventoryItem.
        - The contents of pricePoints can be accessed and manipulated via a Python list
        API.
        - Each member of pricePoints must be a non-negative float.
        - Members cannot be duplicated within pricePoints: each must be must be unique.
        - The attribute and its contents have descriptive titles.  Typically these
        would be message ids.
        
        This declaration creates a field that implements a number of interfaces, among
        them these:
        
        >>> from zope.schema.interfaces import IList, ISequence, ICollection
        >>> IList.providedBy(IInventoryItem['pricePoints'])
        True
        >>> ISequence.providedBy(IInventoryItem['pricePoints'])
        True
        >>> ICollection.providedBy(IInventoryItem['pricePoints'])
        True
        
        Creating a custom collection field
        ----------------------------------
        
        Ideally, custom collection fields have interfaces that inherit appropriately
        from either zope.schema.interfaces.ISequence or
        zope.schema.interfaces.IUnorderedCollection.  Most collection fields should be
        able to subclass zope.schema._field.AbstractCollection to get the necessary
        behavior.  Notice the behavior of the Set field in zope.schema._field: this
        would also be necessary to implement a Bag.
        
        Choices and Vocabularies
        ------------------------
        
        Choice fields are the schema way of spelling enumerated fields and more.  By
        providing a dynamically generated vocabulary, the choices available to a
        choice field can be contextually calculated.
        
        Simple choices do not have to explicitly use vocabularies:
        
        >>> from zope.schema import Choice
        >>> f = Choice((640, 1028, 1600))
        >>> f.validate(640)
        >>> f.validate(960)
        Traceback (most recent call last):
        ...
        ConstraintNotSatisfied: 960
        >>> f.validate('bing')
        Traceback (most recent call last):
        ...
        ConstraintNotSatisfied: bing
        
        More complex choices will want to use registered vocabularies.  Vocabularies
        have a simple interface, as defined in
        zope.schema.interfaces.IBaseVocabulary.  A vocabulary must minimally be able
        to determine whether it contains a value, to create a term object for a value,
        and to return a query interface (or None) to find items in itself.  Term
        objects are an abstraction that wraps a vocabulary value.
        
        The Zope application server typically needs a fuller interface that provides
        "tokens" on its terms: ASCII values that have a one-to-one relationship to the
        values when the vocabulary is asked to "getTermByToken".  If a vocabulary is
        small, it can also support the IIterableVocabulary interface.
        
        If a vocabulary has been registered, then the choice merely needs to pass the
        vocabulary identifier to the "vocabulary" argument of the choice during
        instantiation.
        
        A start to a vocabulary implementation that may do all you need for many simple
        tasks may be found in zope.schema.vocabulary.SimpleVocabulary.  Because
        registered vocabularies are simply callables passed a context, many
        registered vocabularies can simply be functions that rely on SimpleVocabulary:
        
        >>> from zope.schema.vocabulary import SimpleVocabulary
        >>> def myDynamicVocabulary(context):
        ...     v = dynamic_context_calculation_that_returns_an_iterable(context)
        ...     return SimpleVocabulary.fromValues(v)
        ...
        
        The vocabulary interface is simple enough that writing a custom vocabulary is
        not too difficult itself.
        
        Choices and Collections
        -----------------------
        
        Choices are a field type and can be used as a value_type for collections.  Just
        as a collection of an "Int" value_type constrains members to integers, so a
        choice-based value type constrains members to choices within the Choice's
        vocabulary.  Typically in the Zope application server widgets are found not
        only for the collection and the choice field but also for the vocabulary on
        which the choice is based.
        
        Using Choice and Collection Fields within a Widget Framework
        ------------------------------------------------------------
        
        While fields support several use cases, including code documentation and data
        description and even casting, a significant use case influencing their design is
        to support form generation -- generating widgets for a field.  Choice and
        collection fields are expected to be used within widget frameworks.  The
        zope.app approach typically (but configurably) uses multiple dispatches to
        find widgets on the basis of various aspects of the fields.
        
        Widgets for all fields are found by looking up a browser view of the field
        providing an input or display widget view.  Typically there is only a single
        "widget" registered for Choice fields.  When it is looked up, it performs
        another dispatch -- another lookup -- for a widget registered for both the field
        and the vocabulary.  This widget typically has enough information to render
        without a third dispatch.
        
        Collection fields may fire several dispatches.  The first is the usual lookup
        by field.  A single "widget" should be registered for ICollection, which does
        a second lookup by field and value_type constraint, if any, or, theoretically,
        if value_type is None, renders some absolutely generic collection widget that
        allows input of any value imaginable: a check-in of such a widget would be
        unexpected.  This second lookup may find a widget that knows how to render,
        and stop.  However, the value_type may be a choice, which will usually fire a
        third dispatch: a search for a browser widget for the collection field, the
        value_type field, and the vocabulary.  Further lookups may even be configured
        on the basis of uniqueness and other constraints.
        
        This level of indirection may be unnecessary for some applications, and can be
        disabled with simple ZCML changes within `zope.app`.
        
        
        =======
        Sources
        =======
        
        Concepts
        --------
        
        Sources are designed with three concepts:
        
        - The source itself - an iterable
        
        This can return any kind of object it wants. It doesn't have to care
        for browser representation, encoding, ...
        
        - A way to map a value from the iterable to something that can be used
        for form *values* - this is called a token. A token is commonly a
        (unique) 7bit representation of the value.
        
        - A way to map a value to something that can be displayed to the user -
        this is called a title
        
        The last two elements are dispatched using a so called `term`. The
        ITitleTokenizedTerm interface contains a triple of (value, token, term).
        
        Additionally there are some lookup functions to perform the mapping
        between values and terms and tokens and terms.
        
        Sources that require context use a special factory: a context source
        binder that is called with the context and instanciates the source when
        it is actually used.
        
        Sources in Fields
        -----------------
        
        A choice field can be constructed with a source or source name.  When a source
        is used, it will be used as the source for valid values.
        
        Create a source for all odd numbers.
        
        >>> from zope import interface
        >>> from zope.schema.interfaces import ISource, IContextSourceBinder
        >>> class MySource(object):
        ...     interface.implements(ISource)
        ...     divisor = 2
        ...     def __contains__(self, value):
        ...         return bool(value % self.divisor)
        >>> my_source = MySource()
        >>> 1 in my_source
        True
        >>> 2 in my_source
        False
        
        >>> from zope.schema import Choice
        >>> choice = Choice(__name__='number', source=my_source)
        >>> bound = choice.bind(object())
        >>> bound.vocabulary
        <...MySource...>
        
        If a IContextSourceBinder is passed as the `source` argument to Choice, it's
        `bind` method will be called with the context as its only argument.   The
        result must implement ISource and will be used as the source.
        
        >>> def my_binder(context):
        ...     print "Binder was called."
        ...     source = MySource()
        ...     source.divisor = context.divisor
        ...     return source
        >>> interface.directlyProvides(my_binder, IContextSourceBinder)
        
        >>> class Context(object):
        ...     divisor = 3
        
        >>> choice = Choice(__name__='number', source=my_binder)
        >>> bound = choice.bind(Context())
        Binder was called.
        >>> bound.vocabulary
        <...MySource...>
        >>> bound.vocabulary.divisor
        3
        
        When using IContextSourceBinder together with default value, it's
        impossible to validate it on field initialization. Let's check if
        initalization doesn't fail in that case.
        
        >>> choice = Choice(__name__='number', source=my_binder, default=2)
        
        >>> bound = choice.bind(Context())
        Binder was called.
        
        >>> bound.validate(bound.default)
        >>> bound.validate(3)
        Traceback (most recent call last):
        ...
        ConstraintNotSatisfied: 3
        
        It's developer's responsibility to provide a default value that fits the
        constraints when using context-based sources.
        
        
        =================
        Schema Validation
        =================
        
        There are two helper methods to verify schemas and interfaces:
        
        getValidationErrors
        first validates via the zope.schema field validators. If that succeeds the
        invariants are checked.
        getSchemaValidationErrors
        *only* validateds via the zope.schema field validators. The invariants are
        *not* checked.
        
        
        Create an interface to validate against:
        
        >>> import zope.interface
        >>> import zope.schema
        >>> class ITwoInts(zope.interface.Interface):
        ...     a = zope.schema.Int(max=10)
        ...     b = zope.schema.Int(min=5)
        ...
        ...     @zope.interface.invariant
        ...     def a_greater_b(obj):
        ...         print "Checking if a > b"
        ...         if obj.a <= obj.b:
        ...             raise zope.interface.Invalid("%s<=%s" % (obj.a, obj.b))
        ...
        
        Create a silly model:
        
        >>> class TwoInts(object):
        ...     pass
        
        Create an instance of TwoInts but do not set attributes. We get two errors:
        
        >>> ti = TwoInts()
        >>> r = zope.schema.getValidationErrors(ITwoInts, ti)
        >>> r
        [('a', SchemaNotFullyImplemented(...AttributeError...)),
        ('b', SchemaNotFullyImplemented(...AttributeError...))]
        >>> r[0][1].args[0].args
        ("'TwoInts' object has no attribute 'a'",)
        >>> r[1][1].args[0].args
        ("'TwoInts' object has no attribute 'b'",)
        
        The `getSchemaValidationErrors` function returns the same result:
        
        >>> r = zope.schema.getSchemaValidationErrors(ITwoInts, ti)
        >>> r
        [('a', SchemaNotFullyImplemented(...AttributeError...)),
        ('b', SchemaNotFullyImplemented(...AttributeError...))]
        >>> r[0][1].args[0].args
        ("'TwoInts' object has no attribute 'a'",)
        >>> r[1][1].args[0].args
        ("'TwoInts' object has no attribute 'b'",)
        
        Note that see no error from the invariant because the invariants are not
        vaildated if there are other schema errors.
        
        When we set a valid value for `a` we still get the same error for `b`:
        
        >>> ti.a = 11
        >>> errors = zope.schema.getValidationErrors(ITwoInts, ti)
        >>> errors
        [('a', TooBig(11, 10)),
        ('b', SchemaNotFullyImplemented(...AttributeError...))]
        >>> errors[1][1].args[0].args
        ("'TwoInts' object has no attribute 'b'",)
        
        >>> errors[0][1].doc()
        u'Value is too big'
        
        
        After setting a valid value for `a` there is only the error for the missing `b`
        left:
        
        >>> ti.a = 8
        >>> r = zope.schema.getValidationErrors(ITwoInts, ti)
        >>> r
        [('b', SchemaNotFullyImplemented(...AttributeError...))]
        >>> r[0][1].args[0].args
        ("'TwoInts' object has no attribute 'b'",)
        
        
        After setting valid value for `b` the schema is valid so the invariants are
        checked. As `b>a` the invariant fails:
        
        >>> ti.b = 10
        >>> errors = zope.schema.getValidationErrors(ITwoInts, ti)
        Checking if a > b
        >>> errors
        [(None, <zope.interface.exceptions.Invalid instance at 0x...>)]
        
        
        When using `getSchemaValidationErrors` we do not get an error any more:
        
        >>> zope.schema.getSchemaValidationErrors(ITwoInts, ti)
        []
        
        
        Set `b=5` so everything is fine:
        
        >>> ti.b = 5
        >>> zope.schema.getValidationErrors(ITwoInts, ti)
        Checking if a > b
        []
        
        
        Compare ValidationError
        -----------------------
        
        There was an issue with compare validation error with somthing else then an
        exceptions. Let's test if we can compare ValidationErrors with different things
        
        >>> from zope.schema._bootstrapinterfaces import ValidationError
        >>> v1 = ValidationError('one')
        >>> v2 = ValidationError('one')
        >>> v3 = ValidationError('another one')
        
        A ValidationError with the same arguments compares:
        
        >>> v1 == v2
        True
        
        but not with an error with different arguments:
        
        >>> v1 == v3
        False
        
        We can also compare validation erros with other things then errors. This
        was running into an AttributeError in previous versions of zope.schema. e.g.
        AttributeError: 'NoneType' object has no attribute 'args'
        
        >>> v1 == None
        False
        
        >>> v1 == object()
        False
        
        >>> v1 == False
        False
        
        >>> v1 == True
        False
        
        >>> v1 == 0
        False
        
        >>> v1 == 1
        False
        
        >>> v1 == int
        False
        
        If we compare a ValidationError with another validation error based class,
        we will get the following result:
        
        >>> from zope.schema._bootstrapinterfaces import RequiredMissing
        >>> r1 = RequiredMissing('one')
        >>> v1 == r1
        True
        
        
        =======
        CHANGES
        =======
        
        3.5.4 (2009-03-25)
        ------------------
        
        - Don't fail trying to validate default value for Choice fields with
        IContextSourceBinder object given as a source. See
        https://bugs.launchpad.net/zope3/+bug/340416.
        
        - Add an interface for ``DottedName`` field.
        
        - Add ``vocabularyName`` attribute to the ``IChoice`` interface, change
        "vocabulary" attribute description to be more sensible, making it
        ``zope.schema.Field`` instead of plain ``zope.interface.Attribute``.
        
        - Make IBool interface of Bool more important than IFromUnicode so adapters
        registered for IBool take precendence over adapters registered for
        IFromUnicode.
        
        
        3.5.3 (2009-03-10)
        ------------------
        
        - Make Choice and Bool fields implement IFromUnicode interface, because
        they do provide the ``fromUnicode`` method.
        
        - Change package's mailing list address to zope-dev at zope.org, as
        zope3-dev at zope.org is now retired.
        
        - Fix package's documentation formatting. Change package's description.
        
        - Add buildout part that builds Sphinx-generated documentation.
        
        - Remove zpkg-related file.
        
        3.5.2 (2009-02-04)
        ------------------
        
        - Made validation tests compatible with Python 2.5 again (hopefully not
        breaking Python 2.4)
        
        - Added an __all__ package attribute to expose documentation.
        
        3.5.1 (2009-01-31)
        ------------------
        
        - Stop using the old old set type.
        
        - Make tests compatible and silent with Python 2.4.
        
        - Fix __cmp__ method in ValidationError. Show some side effects based on the
        existing __cmp__ implementation. See validation.txt
        
        - Make 'repr' of the ValidationError and its subclasses more sensible. This
        may require you to adapt your doctests for the new style, but now it makes
        much more sense for debugging for developers.
        
        3.5.0a2 (2008-12-11)
        --------------------
        
        - Move zope.testing to "test" extras_require, as it is not needed
        for zope.schema itself.
        
        - Change the order of classes in SET_TYPES tuple, introduced in
        previous release to one that was in 3.4 (SetType, set), because
        third-party code could be dependent on that order. The one
        example is z3c.form's converter.
        
        3.5.0a1 (2008-10-10)
        --------------------
        
        - Added the doctests to the long description.
        
        - Removed use of deprecated 'sets' module when running under Python 2.6.
        
        - Removed spurious doctest failure when running under Python 2.6.
        
        - Added support to bootstrap on Jython.
        
        - Added helper methods for schema validation: ``getValidationErrors``
        and ``getSchemaValidationErrors``.
        
        - zope.schema now works on Python2.5
        
        3.4.0 (2007-09-28)
        ------------------
        
        Added BeforeObjectAssignedEvent that is triggered before the object
        field sets a value.
        
        3.3.0 (2007-03-15)
        ------------------
        
        Corresponds to the version of the zope.schema package shipped as part of
        the Zope 3.3.0 release.
        
        3.2.1 (2006-03-26)
        ------------------
        
        Corresponds to the version of the zope.schema package shipped as part of
        the Zope 3.2.1 release.
        
        Fixed missing import of 'VocabularyRegistryError'.  See
        http://www.zope.org/Collectors/Zope3-dev/544 .
        
        3.2.0 (2006-01-05)
        ------------------
        
        Corresponds to the version of the zope.schema package shipped as part of
        the Zope 3.2.0 release.
        
        Added "iterable" sources to replace vocabularies, which are now deprecated
        and scheduled for removal in Zope 3.3.
        
        3.1.0 (2005-10-03)
        ------------------
        
        Corresponds to the version of the zope.schema package shipped as part of
        the Zope 3.1.0 release.
        
        Allowed 'Choice' fields to take either a 'vocabulary' or a 'source'
        argument (sources are a simpler implementation).
        
        Added 'TimeDelta' and 'ASCIILine' field types.
        
        3.0.0 (2004-11-07)
        ------------------
        
        Corresponds to the version of the zope.schema package shipped as part of
        the Zope X3.0.0 release.
        
Platform: UNKNOWN
