zope.interface.declarations — zope.interface 4.0.1 documentation

# Source code for zope.interface.declarations

    ##############################################################################
    # Copyright (c) 2003 Zope Foundation and Contributors.
    # All Rights Reserved.
    #
    # This software is subject to the provisions of the Zope Public License,
    # Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
    # THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
    # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
    # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
    # FOR A PARTICULAR PURPOSE.
    ##############################################################################
    """Implementation of interface declarations

    There are three flavors of declarations:

      - Declarations are used to simply name declared interfaces.

      - ImplementsDeclarations are used to express the interfaces that a
        class implements (that instances of the class provides).

        Implements specifications support inheriting interfaces.

      - ProvidesDeclarations are used to express interfaces directly
        provided by objects.

    """
    __docformat__ = 'restructuredtext'

    import sys
    from types import FunctionType
    from types import MethodType
    from types import ModuleType
    import warnings
    import weakref

    from zope.interface.advice import addClassAdvisor
    from zope.interface.interface import InterfaceClass
    from zope.interface.interface import SpecificationBase
    from zope.interface.interface import Specification
    from zope.interface._compat import CLASS_TYPES as DescriptorAwareMetaClasses
    from zope.interface._compat import PYTHON3

    # Registry of class-implementation specifications
    BuiltinImplementationSpecifications = {}

    _ADVICE_ERROR = ('Class advice impossible in Python3.  '
                     'Use the @%s class decorator instead.')

    _ADVICE_WARNING = ('The %s API is deprecated, and will not work in Python3  '
                       'Use the @%s class decorator instead.')

    class named(object):

        def __init__(self, name):
            self.name = name

        def __call__(self, ob):
            ob.__component_name__ = self.name
            return ob

    class Declaration(Specification):
        """Interface declarations"""

        def __init__(self, *interfaces):
            Specification.__init__(self, _normalizeargs(interfaces))

        def changed(self, originally_changed):
            Specification.changed(self, originally_changed)
            try:
                del self._v_attrs
            except AttributeError:
                pass

        def __contains__(self, interface):
            """Test whether an interface is in the specification
            """

            return self.extends(interface) and interface in self.interfaces()

        def __iter__(self):
            """Return an iterator for the interfaces in the specification
            """
            return self.interfaces()

        def flattened(self):
            """Return an iterator of all included and extended interfaces
            """
            return iter(self.__iro__)

        def __sub__(self, other):
            """Remove interfaces from a specification
            """
            return Declaration(
                *[i for i in self.interfaces()
                    if not [j for j in other.interfaces()
                            if i.extends(j, 0)]
                    ]
                    )

        def __add__(self, other):
            """Add two specifications or a specification and an interface
            """
            seen = {}
            result = []
            for i in self.interfaces():
                seen[i] = 1
                result.append(i)
            for i in other.interfaces():
                if i not in seen:
                    seen[i] = 1
                    result.append(i)

            return Declaration(*result)

        __radd__ = __add__

    ##############################################################################
    #
    # Implementation specifications
    #
    # These specify interfaces implemented by instances of classes

    class Implements(Declaration):

        # class whose specification should be used as additional base
        inherit = None

        # interfaces actually declared for a class
        declared = ()

        __name__ = '?'

        def __repr__(self):
            return '<implementedBy %s>' % (self.__name__)

        def __reduce__(self):
            return implementedBy, (self.inherit, )

    def implementedByFallback(cls):
        """Return the interfaces implemented for a class' instances

          The value returned is an IDeclaration.
        """
        try:
            spec = cls.__dict__.get('__implemented__')
        except AttributeError:

            # we can't get the class dict. This is probably due to a
            # security proxy.  If this is the case, then probably no
            # descriptor was installed for the class.

            # We don't want to depend directly on zope.security in
            # zope.interface, but we'll try to make reasonable
            # accommodations in an indirect way.

            # We'll check to see if there's an implements:

            spec = getattr(cls, '__implemented__', None)
            if spec is None:
                # There's no spec stred in the class. Maybe its a builtin:
                spec = BuiltinImplementationSpecifications.get(cls)
                if spec is not None:
                    return spec
                return _empty

            if spec.__class__ == Implements:
                # we defaulted to _empty or there was a spec. Good enough.
                # Return it.
                return spec

            # TODO: need old style __implements__ compatibility?
            # Hm, there's an __implemented__, but it's not a spec. Must be
            # an old-style declaration. Just compute a spec for it
            return Declaration(*_normalizeargs((spec, )))

        if isinstance(spec, Implements):
            return spec

        if spec is None:
            spec = BuiltinImplementationSpecifications.get(cls)
            if spec is not None:
                return spec

        # TODO: need old style __implements__ compatibility?
        if spec is not None:
            # old-style __implemented__ = foo declaration
            spec = (spec, ) # tuplefy, as it might be just an int
            spec = Implements(*_normalizeargs(spec))
            spec.inherit = None    # old-style implies no inherit
            del cls.__implemented__ # get rid of the old-style declaration
        else:
            try:
                bases = cls.__bases__
            except AttributeError:
                if not callable(cls):
                    raise TypeError("ImplementedBy called for non-factory", cls)
                bases = ()

            spec = Implements(*[implementedBy(c) for c in bases])
            spec.inherit = cls

        spec.__name__ = (getattr(cls, '__module__', '?') or '?') + \
                        '.' + (getattr(cls, '__name__', '?') or '?')

        try:
            cls.__implemented__ = spec
            if not hasattr(cls, '__providedBy__'):
                cls.__providedBy__ = objectSpecificationDescriptor

            if (isinstance(cls, DescriptorAwareMetaClasses)
                and
                '__provides__' not in cls.__dict__):
                # Make sure we get a __provides__ descriptor
                cls.__provides__ = ClassProvides(
                    cls,
                    getattr(cls, '__class__', type(cls)),
                    )

        except TypeError:
            if not isinstance(cls, type):
                raise TypeError("ImplementedBy called for non-type", cls)
            BuiltinImplementationSpecifications[cls] = spec

        return spec

    implementedBy = implementedByFallback

    def classImplementsOnly(cls, *interfaces):
        """Declare the only interfaces implemented by instances of a class

          The arguments after the class are one or more interfaces or interface
          specifications (``IDeclaration`` objects).

          The interfaces given (including the interfaces in the specifications)
          replace any previous declarations.
        """
        spec = implementedBy(cls)
        spec.declared = ()
        spec.inherit = None
        classImplements(cls, *interfaces)

    def classImplements(cls, *interfaces):
        """Declare additional interfaces implemented for instances of a class

          The arguments after the class are one or more interfaces or
          interface specifications (``IDeclaration`` objects).

          The interfaces given (including the interfaces in the specifications)
          are added to any interfaces previously declared.
        """
        spec = implementedBy(cls)
        spec.declared += tuple(_normalizeargs(interfaces))

        # compute the bases
        bases = []
        seen = {}
        for b in spec.declared:
            if b not in seen:
                seen[b] = 1
                bases.append(b)

        if spec.inherit is not None:

            for c in spec.inherit.__bases__:
                b = implementedBy(c)
                if b not in seen:
                    seen[b] = 1
                    bases.append(b)

        spec.__bases__ = tuple(bases)

    def _implements_advice(cls):
        interfaces, classImplements = cls.__dict__['__implements_advice_data__']
        del cls.__implements_advice_data__
        classImplements(cls, *interfaces)
        return cls

    class implementer:
        """Declare the interfaces implemented by instances of a class.

          This function is called as a class decorator.

          The arguments are one or more interfaces or interface
          specifications (IDeclaration objects).

          The interfaces given (including the interfaces in the
          specifications) are added to any interfaces previously
          declared.

          Previous declarations include declarations for base classes
          unless implementsOnly was used.

          This function is provided for convenience. It provides a more
          convenient way to call classImplements. For example::

            @implementer(I1)
            class C(object):
                pass

          is equivalent to calling::

            classImplements(C, I1)

          after the class has been created.
          """

        def __init__(self, *interfaces):
            self.interfaces = interfaces

        def __call__(self, ob):
            if isinstance(ob, DescriptorAwareMetaClasses):
                classImplements(ob, *self.interfaces)
                return ob

            spec = Implements(*self.interfaces)
            try:
                ob.__implemented__ = spec
            except AttributeError:
                raise TypeError("Can't declare implements", ob)
            return ob

    class implementer_only:
        """Declare the only interfaces implemented by instances of a class

          This function is called as a class decorator.

          The arguments are one or more interfaces or interface
          specifications (IDeclaration objects).

          Previous declarations including declarations for base classes
          are overridden.

          This function is provided for convenience. It provides a more
          convenient way to call classImplementsOnly. For example::

            @implementer_only(I1)
            class C(object): pass

          is equivalent to calling::

            classImplementsOnly(I1)

          after the class has been created.
          """

        def __init__(self, *interfaces):
            self.interfaces = interfaces

        def __call__(self, ob):
            if isinstance(ob, (FunctionType, MethodType)):
                # XXX Does this decorator make sense for anything but classes?
                # I don't think so. There can be no inheritance of interfaces
                # on a method pr function....
                raise ValueError('The implementer_only decorator is not '
                                 'supported for methods or functions.')
            else:
                # Assume it's a class:
                classImplementsOnly(ob, *self.interfaces)
                return ob

    def _implements(name, interfaces, classImplements):
        # This entire approach is invalid under Py3K.  Don't even try to fix
        # the coverage for this block there. :(
        if PYTHON3: #pragma NO COVER
            raise TypeError('Class advice impossible in Python3')
        frame = sys._getframe(2)
        locals = frame.f_locals

        # Try to make sure we were called from a class def. In 2.2.0 we can't
        # check for __module__ since it doesn't seem to be added to the locals
        # until later on.
        if locals is frame.f_globals or '__module__' not in locals:
            raise TypeError(name+" can be used only from a class definition.")

        if '__implements_advice_data__' in locals:
            raise TypeError(name+" can be used only once in a class definition.")

        locals['__implements_advice_data__'] = interfaces, classImplements
        addClassAdvisor(_implements_advice, depth=3)

    def implements(*interfaces):
        """Declare interfaces implemented by instances of a class

          This function is called in a class definition.

          The arguments are one or more interfaces or interface
          specifications (IDeclaration objects).

          The interfaces given (including the interfaces in the
          specifications) are added to any interfaces previously
          declared.

          Previous declarations include declarations for base classes
          unless implementsOnly was used.

          This function is provided for convenience. It provides a more
          convenient way to call classImplements. For example::

            implements(I1)

          is equivalent to calling::

            classImplements(C, I1)

          after the class has been created.
        """
        # This entire approach is invalid under Py3K.  Don't even try to fix
        # the coverage for this block there. :(
        if PYTHON3: #pragma NO COVER
            raise TypeError(_ADVICE_ERROR % 'implementer')
        _implements("implements", interfaces, classImplements)

    def implementsOnly(*interfaces):
        """Declare the only interfaces implemented by instances of a class

          This function is called in a class definition.

          The arguments are one or more interfaces or interface
          specifications (IDeclaration objects).

          Previous declarations including declarations for base classes
          are overridden.

          This function is provided for convenience. It provides a more
          convenient way to call classImplementsOnly. For example::

            implementsOnly(I1)

          is equivalent to calling::

            classImplementsOnly(I1)

          after the class has been created.
        """
        # This entire approach is invalid under Py3K.  Don't even try to fix
        # the coverage for this block there. :(
        if PYTHON3: #pragma NO COVER
            raise TypeError(_ADVICE_ERROR % 'implementer_only')
        _implements("implementsOnly", interfaces, classImplementsOnly)

    ##############################################################################
    #
    # Instance declarations

    class Provides(Declaration):  # Really named ProvidesClass
        """Implement __provides__, the instance-specific specification

        When an object is pickled, we pickle the interfaces that it implements.
        """

        def __init__(self, cls, *interfaces):
            self.__args = (cls, ) + interfaces
            self._cls = cls
            Declaration.__init__(self, *(interfaces + (implementedBy(cls), )))

        def __reduce__(self):
            return Provides, self.__args

        __module__ = 'zope.interface'

        def __get__(self, inst, cls):
            """Make sure that a class __provides__ doesn't leak to an instance
            """
            if inst is None and cls is self._cls:
                # We were accessed through a class, so we are the class'
                # provides spec. Just return this object, but only if we are
                # being called on the same class that we were defined for:
                return self

            raise AttributeError('__provides__')

    ProvidesClass = Provides

    # Registry of instance declarations
    # This is a memory optimization to allow objects to share specifications.
    InstanceDeclarations = weakref.WeakValueDictionary()

    def Provides(*interfaces):
        """Cache instance declarations

          Instance declarations are shared among instances that have the same
          declaration. The declarations are cached in a weak value dictionary.
        """
        spec = InstanceDeclarations.get(interfaces)
        if spec is None:
            spec = ProvidesClass(*interfaces)
            InstanceDeclarations[interfaces] = spec

        return spec

    Provides.__safe_for_unpickling__ = True

    def directlyProvides(object, *interfaces):
        """Declare interfaces declared directly for an object

          The arguments after the object are one or more interfaces or interface
          specifications (``IDeclaration`` objects).

          The interfaces given (including the interfaces in the specifications)
          replace interfaces previously declared for the object.
        """
        cls = getattr(object, '__class__', None)
        if cls is not None and getattr(cls,  '__class__', None) is cls:
            # It's a meta class (well, at least it it could be an extension class)
            # Note that we can't get here from Py3k tests:  there is no normal
            # class which isn't descriptor aware.
            if not isinstance(object,
                              DescriptorAwareMetaClasses): #pragma NO COVER Py3k
                raise TypeError("Attempt to make an interface declaration on a "
                                "non-descriptor-aware class")

        interfaces = _normalizeargs(interfaces)
        if cls is None:
            cls = type(object)

        issub = False
        for damc in DescriptorAwareMetaClasses:
            if issubclass(cls, damc):
                issub = True
                break
        if issub:
            # we have a class or type.  We'll use a special descriptor
            # that provides some extra caching
            object.__provides__ = ClassProvides(object, cls, *interfaces)
        else:
            object.__provides__ = Provides(cls, *interfaces)

    def alsoProvides(object, *interfaces):
        """Declare interfaces declared directly for an object

        The arguments after the object are one or more interfaces or interface
        specifications (``IDeclaration`` objects).

        The interfaces given (including the interfaces in the specifications) are
        added to the interfaces previously declared for the object.
        """
        directlyProvides(object, directlyProvidedBy(object), *interfaces)

    def noLongerProvides(object, interface):
        """ Removes a directly provided interface from an object.
        """
        directlyProvides(object, directlyProvidedBy(object) - interface)
        if interface.providedBy(object):
            raise ValueError("Can only remove directly provided interfaces.")

    class ClassProvidesBaseFallback(object):

        def __get__(self, inst, cls):
            if cls is self._cls:
                # We only work if called on the class we were defined for

                if inst is None:
                    # We were accessed through a class, so we are the class'
                    # provides spec. Just return this object as is:
                    return self

                return self._implements

            raise AttributeError('__provides__')

    ClassProvidesBasePy = ClassProvidesBaseFallback # BBB
    ClassProvidesBase = ClassProvidesBaseFallback

    # Try to get C base:
    try:
        import _zope_interface_coptimizations
    except ImportError:  #pragma NO COVERAGE
        pass
    else:  #pragma NO COVERAGE
        from _zope_interface_coptimizations import ClassProvidesBase

    class ClassProvides(Declaration, ClassProvidesBase):
        """Special descriptor for class __provides__

        The descriptor caches the implementedBy info, so that
        we can get declarations for objects without instance-specific
        interfaces a bit quicker.
        """
        def __init__(self, cls, metacls, *interfaces):
            self._cls = cls
            self._implements = implementedBy(cls)
            self.__args = (cls, metacls, ) + interfaces
            Declaration.__init__(self, *(interfaces + (implementedBy(metacls), )))

        def __reduce__(self):
            return self.__class__, self.__args

        # Copy base-class method for speed
        __get__ = ClassProvidesBase.__get__

    def directlyProvidedBy(object):
        """Return the interfaces directly provided by the given object

        The value returned is an ``IDeclaration``.
        """
        provides = getattr(object, "__provides__", None)
        if (provides is None # no spec
            or
            # We might have gotten the implements spec, as an
            # optimization. If so, it's like having only one base, that we
            # lop off to exclude class-supplied declarations:
            isinstance(provides, Implements)
            ):
            return _empty

        # Strip off the class part of the spec:
        return Declaration(provides.__bases__[:-1])

    def classProvides(*interfaces):
        """Declare interfaces provided directly by a class

          This function is called in a class definition.

          The arguments are one or more interfaces or interface specifications
          (``IDeclaration`` objects).

          The given interfaces (including the interfaces in the specifications)
          are used to create the class's direct-object interface specification.
          An error will be raised if the module class has an direct interface
          specification. In other words, it is an error to call this function more
          than once in a class definition.

          Note that the given interfaces have nothing to do with the interfaces
          implemented by instances of the class.

          This function is provided for convenience. It provides a more convenient
          way to call directlyProvides for a class. For example::

            classProvides(I1)

          is equivalent to calling::

            directlyProvides(theclass, I1)

          after the class has been created.
        """
        # This entire approach is invalid under Py3K.  Don't even try to fix
        # the coverage for this block there. :(

        if PYTHON3: #pragma NO COVER
            raise TypeError(_ADVICE_ERROR % 'provider')

        frame = sys._getframe(1)
        locals = frame.f_locals

        # Try to make sure we were called from a class def
        if (locals is frame.f_globals) or ('__module__' not in locals):
            raise TypeError("classProvides can be used only from a "
                            "class definition.")

        if '__provides__' in locals:
            raise TypeError(
                "classProvides can only be used once in a class definition.")

        locals["__provides__"] = _normalizeargs(interfaces)

        addClassAdvisor(_classProvides_advice, depth=2)

    def _classProvides_advice(cls):
        # This entire approach is invalid under Py3K.  Don't even try to fix
        # the coverage for this block there. :(
        interfaces = cls.__dict__['__provides__']
        del cls.__provides__
        directlyProvides(cls, *interfaces)
        return cls

    class provider:
        """Class decorator version of classProvides"""

        def __init__(self, *interfaces):
            self.interfaces = interfaces

        def __call__(self, ob):
            directlyProvides(ob, *self.interfaces)
            return ob

    def moduleProvides(*interfaces):
        """Declare interfaces provided by a module

        This function is used in a module definition.

        The arguments are one or more interfaces or interface specifications
        (``IDeclaration`` objects).

        The given interfaces (including the interfaces in the specifications) are
        used to create the module's direct-object interface specification.  An
        error will be raised if the module already has an interface specification.
        In other words, it is an error to call this function more than once in a
        module definition.

        This function is provided for convenience. It provides a more convenient
        way to call directlyProvides. For example::

          moduleImplements(I1)

        is equivalent to::

          directlyProvides(sys.modules[__name__], I1)
        """
        frame = sys._getframe(1)
        locals = frame.f_locals

        # Try to make sure we were called from a class def
        if (locals is not frame.f_globals) or ('__name__' not in locals):
            raise TypeError(
                "moduleProvides can only be used from a module definition.")

        if '__provides__' in locals:
            raise TypeError(
                "moduleProvides can only be used once in a module definition.")

        locals["__provides__"] = Provides(ModuleType,
                                          *_normalizeargs(interfaces))

    ##############################################################################
    #
    # Declaration querying support

    # XXX:  is this a fossil?  Nobody calls it, no unit tests exercise it, no
    #       doctests import it, and the package __init__ doesn't import it.
    def ObjectSpecification(direct, cls):
        """Provide object specifications

        These combine information for the object and for it's classes.
        """
        return Provides(cls, direct) #pragma NO COVER fossil

    def getObjectSpecificationFallback(ob):

        provides = getattr(ob, '__provides__', None)
        if provides is not None:
            if isinstance(provides, SpecificationBase):
                return provides

        try:
            cls = ob.__class__
        except AttributeError:
            # We can't get the class, so just consider provides
            return _empty

        return implementedBy(cls)

    getObjectSpecification = getObjectSpecificationFallback

    def providedByFallback(ob):

        # Here we have either a special object, an old-style declaration
        # or a descriptor

        # Try to get __providedBy__
        try:
            r = ob.__providedBy__
        except AttributeError:
            # Not set yet. Fall back to lower-level thing that computes it
            return getObjectSpecification(ob)

        try:
            # We might have gotten a descriptor from an instance of a
            # class (like an ExtensionClass) that doesn't support
            # descriptors.  We'll make sure we got one by trying to get
            # the only attribute, which all specs have.
            r.extends

        except AttributeError:

            # The object's class doesn't understand descriptors.
            # Sigh. We need to get an object descriptor, but we have to be
            # careful.  We want to use the instance's __provides__, if
            # there is one, but only if it didn't come from the class.

            try:
                r = ob.__provides__
            except AttributeError:
                # No __provides__, so just fall back to implementedBy
                return implementedBy(ob.__class__)

            # We need to make sure we got the __provides__ from the
            # instance. We'll do this by making sure we don't get the same
            # thing from the class:

            try:
                cp = ob.__class__.__provides__
            except AttributeError:
                # The ob doesn't have a class or the class has no
                # provides, assume we're done:
                return r

            if r is cp:
                # Oops, we got the provides from the class. This means
                # the object doesn't have it's own. We should use implementedBy
                return implementedBy(ob.__class__)

        return r
    providedBy = providedByFallback

    class ObjectSpecificationDescriptorFallback(object):
        """Implement the `__providedBy__` attribute

        The `__providedBy__` attribute computes the interfaces peovided by
        an object.
        """

        def __get__(self, inst, cls):
            """Get an object specification for an object
            """
            if inst is None:
                return getObjectSpecification(cls)

            provides = getattr(inst, '__provides__', None)
            if provides is not None:
                return provides

            return implementedBy(cls)

    ObjectSpecificationDescriptor = ObjectSpecificationDescriptorFallback

    ##############################################################################

    def _normalizeargs(sequence, output = None):
        """Normalize declaration arguments

        Normalization arguments might contain Declarions, tuples, or single
        interfaces.

        Anything but individial interfaces or implements specs will be expanded.
        """
        if output is None:
            output = []

        cls = sequence.__class__
        if InterfaceClass in cls.__mro__ or Implements in cls.__mro__:
            output.append(sequence)
        else:
            for v in sequence:
                _normalizeargs(v, output)

        return output

    _empty = Declaration()

    try:
        import _zope_interface_coptimizations
    except ImportError: #pragma NO COVER
        pass
    else: #pragma NO COVER PyPy
        from _zope_interface_coptimizations import implementedBy
        from _zope_interface_coptimizations import providedBy
        from _zope_interface_coptimizations import getObjectSpecification
        from _zope_interface_coptimizations import ObjectSpecificationDescriptor

    objectSpecificationDescriptor = ObjectSpecificationDescriptor()