Return a list of all <__base_class> based classes found in <file>

def __find_child_classes(self, file):
        """
        Return a list of all <__base_class> based classes found in <file>
        """

        child_classes = []
        folder, name = os.path.split(file)
        name = os.path.splitext(name)[0]

        import imp
        module = imp.load_source(name, file)

        def filter_classes(m):
            if inspect.isclass(m):
                if inspect.getmro(m)[1] == self.__base_class:
                    return True
            return False

        for name, obj in inspect.getmembers(module, filter_classes):
            child_classes.append(obj)

        return child_classes