class DerivedSet(set):

    """The simplest possible class derived from the builtin set?
    It's basically the same, but with a trivially extended __init__
    that takes an (optional) keyword argument.


    DOCTESTS:

    (A)-(D):
    With no arguments, or with a single iterable argument,
    both set and DerivedSet yield the obvious results:

    >>> set()
    set([])

    >>> DerivedSet()
    DerivedSet([])

    >>> set([1])
    set([1])

    >>> DerivedSet([1])
    DerivedSet([1])



    Let's now exercise DerivedSet's extended functionality.    

    First, pass in a debugString AS A POSITIONAL ARGUMENT.

    (E):
    The builtin set doesn't expect this, and fails accordingly:
    
    >>> set([1], 'print this')
    Traceback (most recent call last):
        ...
    TypeError: set expected at most 1 arguments, got 2

    whereas (F):
    The DerivedSet knows to print our message:
    
    >>> DerivedSet([1], 'print this')
    [debugString: print this]
    DerivedSet([1])


    Next, pass debugString in AS A KEYWORD ARGUMENT instead.
    
    (G):
    If your Python has had bug #1119418 fixed (i.e.: 2.4.2 or later),
    builtin set should complain about the unexpected keyword argument:

    >>> set(debugString = 'print this')    ## (G): expect to fail if bug #1119418 not fixed (i.e.: version < 2.4.2c1)
    Traceback (most recent call last):
        ...
    TypeError: set() does not take keyword arguments

    [NB: Expect test (G) to fail if your Python has NOT had
         bug #1119418 fixed (i.e.: it's earlier than 2.4.2c1).]


    Finally (H):
    As long as they are not passed down to base classes that cannot,
    surely derived classes should be able to accept keyword argument(s):

    >>> DerivedSet(debugString = 'print this')    ## (H): should pass -- but seems to fail if version >= 2.4.2c1 (presumably broken by 'fix' for bug #1119418)
    [debugString: print this]
    DerivedSet([])

    Unfortunately, although debugString is clearly not passed to set,
    Python 2.4.2 raises the exact same exception for DerivedSet as for
    the builtin set.  Eek!  Seems like someone's been over-zealous...

    [NB: Expect test (H) to fail if your Python HAS had
         bug #1119418 'fixed' (i.e.: it's 2.4.2c1 or later)!]
    """
    
    def __init__(self, initialElements = [], debugString = None):
        """Print debugString if provided."""
        if debugString:
            print "[debugString: %s]" % (debugString,),
        set.__init__(self, initialElements)





if __name__ == "__main__":

    import doctest
    doctest.testmod()