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itersubclasses(cls) returns a generator over all subclasses of cls, in depth first order. cls must be a new-style class; old-style classes are not supported.

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def itersubclasses(cls, _seen=None):
    """
    itersubclasses(cls)

    Generator over all subclasses of a given class, in depth first order.

    >>> list(itersubclasses(int)) == [bool]
    True
    >>> class A(object): pass
    >>> class B(A): pass
    >>> class C(A): pass
    >>> class D(B,C): pass
    >>> class E(D): pass
    >>> 
    >>> for cls in itersubclasses(A):
    ...     print(cls.__name__)
    B
    D
    E
    C
    >>> # get ALL (new-style) classes currently defined
    >>> [cls.__name__ for cls in itersubclasses(object)] #doctest: +ELLIPSIS
    ['type', ...'tuple', ...]
    """
    
    if not isinstance(cls, type):
        raise TypeError('itersubclasses must be called with '
                        'new-style classes, not %.100r' % cls)
    if _seen is None: _seen = set()
    try:
        subs = cls.__subclasses__()
    except TypeError: # fails only when cls is type
        subs = cls.__subclasses__(cls)
    for sub in subs:
        if sub not in _seen:
            _seen.add(sub)
            yield sub
            for sub in itersubclasses(sub, _seen):
                yield sub


if __name__ == '__main__':
    import doctest
    doctest.testmod(verbose=1)

itersubclasses returns all concrete subclasses of the given class; abstract base classes are not considered.

This same code runs in all Python versions from 2.4 up to 3.1; with minimal modifications can be used even in 2.3.

See the function docstring for usage patterns.

2 comments

Eric-Olivier LE BIGOT 12 years, 1 month ago  # | flag

+1: Thank you! now I know about __subclasses__!

Benjamin 12 years ago  # | flag

Likewise and now that I'm aware of it I have already started using it!