The class classmethod_descriptor implements classmethods for builtin functions. Unlike the plain classmethod class (which is used for Python classmethods), instances of classmethod_descriptor are callable. However, calling them is unlikely to happen in practice: the only way to obtain such an object is to extract from the class __dict__.

Therefore, the implementation of __call__ does not need to be optimized: we can just call __get__ and then call the result. Doing that allows a simpler implementation of PEP 590.