Exception factory

exc.py

# This code is public domain. Copy away!

exception_classes = dict(
    type = TypeError,
    value = ValueError,
    key = KeyError,
    index = IndexError #, ...
    )

def Exc(kind):
    """
    Exc('a/b/c') is a class inhering from Exc('a/b'), which is
    a class inheriting from Exc('a'), which is a class inheriting
    from Exception.

    The point of this facility is 1) to avoid typing crap like:

    class BlahException(Exception):
        "Base class for exceptions about blah!"

    And 2) to use a different exception class for every exception
    site.
    """
    if kind in exception_classes:
        return exception_classes[kind]
    else:
        if "/" in kind:
            split = kind.split("/")
            basekind = "/".join(split[:-1])
            base = Exc(basekind)
        else:
            base = Exception
        cls = type(kind, (base,), {})
        exception_classes[kind] = cls
        return cls

#############

if __name__ == '__main__':

    import sys
    fruit = sys.argv[1]

    try:
        if fruit in ('lemon', 'lime', 'grapefruit'):
            raise Exc('value/too_sour')('%ss are too sour!' % fruit)
        elif fruit == 'jalapeno':
            raise Exc('value/too_spicy')('%ss are too spicy!' % fruit)
        print("Nom nom")
    except Exc('value/too_sour'):
        print('I did not eat the fruit because it was too sour...')
    except ValueError:
        print('I did not eat the fruit for some reason.')