Python: Mapping arguments to their default values

Using inspect.getargspec or the getargspec implemention in my previous post, we can build a dictionary mapping a callable's argument names to their default values:

def getargmap(obj, default=None):
    """Get dictionary mapping callable's arguments to their
       default values

    Arguments without default values in the callable's argument
    specification are mapped to the value given by the default
    argument.
    """
    spec = getargspec(obj)
    argmap = dict.fromkeys(spec[0], default)
    argmap.update(zip(spec[0][-len(spec[3]):], spec[3]))
    return argmap