# Scripts/subclassing-objective-c

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…

## subclassing-objective-c.py

    #!/usr/bin/env python
    # This is a doctest
    """
    =========================================
    Subclassing Objective-C classes in Python
    =========================================

    It is possible to subclass any existing Objective-C class in python.

    We start by importing the interface to the Objective-C runtime, although
    you'd normally use wrappers for the various frameworks, and then locate
    the class we'd like to subclass::

        >>> import objc
        >>> NSEnumerator = objc.lookUpClass('NSEnumerator')
        >>> NSEnumerator
        <objective-c class NSEnumerator at 0xa0a039a8>

    You can then define a subclass of this class using the usual syntax::

        >>> class MyEnumerator (NSEnumerator):
        ...    __slots__ = ('cnt',)
        ...    #
        ...    # Start of the method definitions:
        ...    def init(self):
        ...        self.cnt = 10
        ...        return self
        ...    #
        ...    def nextObject(self):
        ...        if self.cnt == 0:
        ...            return None
        ...        self.cnt -= 1
        ...        return self.cnt
        ...    #
        ...    def __del__(self):
        ...        global DEALLOC_COUNT
        ...        DEALLOC_COUNT = DEALLOC_COUNT + 1

    To check that our instances our deallocated we maintain a ``DEALLOC_COUNT``::

        >>> DEALLOC_COUNT=0

    As always, the creation of instances of Objective-C classes looks a bit odd
    for Python programs:

        >>> obj = MyEnumerator.alloc().init()
        >>> obj.allObjects()
        (9, 8, 7, 6, 5, 4, 3, 2, 1, 0)

    Destroy our reference to the object, to check if it will be deallocated::

       >>> del obj
       >>> DEALLOC_COUNT
       1

    """
    import doctest

    import __main__

    doctest.testmod(__main__, verbose=1)