def __check_classes(self):
<EOL>msg = (<EOL>"<STR_LIT>"<EOL>"<STR_LIT>"<EOL>)<EOL>if not issubclass(self.authentication_class, Authentication):<EOL><INDENT>raise exceptions.InitializationFailure(<EOL>message=msg.format("<STR_LIT>")<EOL>)<EOL><DEDENT>if not issubclass(self.configuration_class, Configuration):<EOL><INDENT>raise exceptions.InitializationFailure(<EOL>message=msg.format("<STR_LIT>")<EOL>)<EOL><DEDENT>if not issubclass(self.responses_class, Responses):<EOL><INDENT>raise exceptions.InitializationFailure(<EOL>message=msg.format("<STR_LIT>")<EOL>)<EOL><DEDENT>
Check if any of the default classes (`Authentication`, `Configuration`
and / or `Responses`) have been overwitten and if they're still valid