kms

Setting Class Names Dynamically in Python

I’m finishing up my QuickCheck implementation for Python. I’m writing generator combinators to make it easier to make new generators. Since the generators I’m using are just classes with a class method arbitrary, the combinators dynamically create classes:

def a_combinator(generator1, generator2):
    class a_combinator_class(...):
        @classmethod
        def arbitrary():
            ...
    return a_combinator_class

However, this leaves us with an issue. I would like to be able to display a name for the generator. For generators which aren’t constructed with combinators, we can just call generator.__name__, but this doesn’t work for generator combinators. With the above combinator, that would show a_combinator_class no matter what generators we pass into the combinator. It would be better if it showed a_combinator(generator1, generator2). We can do this by setting __name__ on a_combinator_class:

def a_combinator(generator1, generator2):
    class a_combinator_class(...):
        ...
    a_combinator_class.__name__ = ''.join([
        'a_combinator(',
        ', '.join([
            generator1.__name__,
            generator2.__name__
        ]),
        ')'
    ])
    return a_combinator_class