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===================================
Verifying interface implementations
===================================

The ``zope.interface.verify`` module provides functions that test whether a
given interface is implemented by a class or provided by an object, resp.


Verifying classes
=================

This is covered by unit tests defined in ``zope.interface.tests.test_verify``.


Verifying objects
=================

An object provides an interface if

- either its class declares that it implements the interfaces, or the object
  declares that it directly provides the interface

- the object defines all the methods required by the interface

- all the methods have the correct signature

- the object defines all non-method attributes required by the interface

This doctest currently covers only the latter item.

Testing for attributes
----------------------

Attributes of the object, be they defined by its class or added by its
``__init__`` method, will be recognized:

.. doctest::

   >>> from zope.interface import Interface, Attribute, implements
   >>> from zope.interface.exceptions import BrokenImplementation
   >>> class IFoo(Interface):
   ...     x = Attribute("The X attribute")
   ...     y = Attribute("The Y attribute")

   >>> class Foo(object):
   ...     implements(IFoo)
   ...     x = 1
   ...     def __init__(self):
   ...         self.y = 2

   >>> from zope.interface.verify import verifyObject
   >>> verifyObject(IFoo, Foo())
   True

If either attribute is missing, verification will fail:

.. doctest::

   >>> class Foo(object):
   ...     implements(IFoo)
   ...     x = 1
   >>> try: #doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
   ...     verifyObject(IFoo, Foo())
   ... except BrokenImplementation, e:
   ...     print str(e)
   An object has failed to implement interface <InterfaceClass ...IFoo>
   <BLANKLINE>
           The y attribute was not provided.
   <BLANKLINE>
   >>> class Foo(object):
   ...     implements(IFoo)
   ...     def __init__(self):
   ...         self.y = 2
   >>> try: #doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
   ...     verifyObject(IFoo, Foo())
   ... except BrokenImplementation, e:
   ...     print str(e)
   An object has failed to implement interface <InterfaceClass ...IFoo>
   <BLANKLINE>
           The x attribute was not provided.
   <BLANKLINE>

If an attribute is implemented as a property that raises an AttributeError
when trying to get its value, the attribute is considered missing:

.. doctest::

   >>> class IFoo(Interface):
   ...     x = Attribute('The X attribute')
   >>> class Foo(object):
   ...     implements(IFoo)
   ...     @property
   ...     def x(self):
   ...         raise AttributeError
   >>> try: #doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
   ...     verifyObject(IFoo, Foo())
   ... except BrokenImplementation, e:
   ...     print str(e)
   An object has failed to implement interface <InterfaceClass ...IFoo>
   <BLANKLINE>
           The x attribute was not provided.
   <BLANKLINE>

Any other exception raised by a property will propagate to the caller of
``verifyObject``:

.. doctest::

   >>> class Foo(object):
   ...     implements(IFoo)
   ...     @property
   ...     def x(self):
   ...         raise Exception
   >>> verifyObject(IFoo, Foo())
   Traceback (most recent call last):
   Exception

Of course, broken properties that are not required by the interface don't do
any harm:

.. doctest::

   >>> class Foo(object):
   ...     implements(IFoo)
   ...     x = 1
   ...     @property
   ...     def y(self):
   ...         raise Exception
   >>> verifyObject(IFoo, Foo())
   True

Name	Size	Last Modified	Owner	Permissions
Makefile	5.461 KB	February 28 2013 6:51:06	root	0644
README.rst	24.32 KB	February 28 2013 6:51:06	root	0644
README.ru.rst	33.185 KB	February 28 2013 6:51:06	root	0644
adapter.rst	14.796 KB	February 28 2013 6:51:06	root	0644
adapter.ru.rst	20.673 KB	February 28 2013 6:51:06	root	0644
api.rst	21.021 KB	February 28 2013 6:51:06	root	0644
conf.py	7.985 KB	February 28 2013 6:51:06	root	0644
foodforthought.rst	1.701 KB	February 28 2013 6:51:06	root	0644
hacking.rst	10.583 KB	February 28 2013 6:51:06	root	0644
human.rst	6.275 KB	February 28 2013 6:51:06	root	0644
human.ru.rst	10.431 KB	February 28 2013 6:51:06	root	0644
index.rst	0.608 KB	February 28 2013 6:51:06	root	0644
make.bat	4.99 KB	February 28 2013 6:51:06	root	0644
verify.rst	3.52 KB	February 28 2013 6:51:06	root	0644

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