New submission from Finn Mason <finnjavie...@gmail.com>:
In _collections_abc.py is a private function titled `_check_methods`. It takes a class and a number of method names (as strings), checks if the class has all of the methods, and returns NotImplemented if any are missing. The code is below: ``` def _check_methods(C, *methods): mro = C.__mro__ for method in methods: for B in mro: if method in B.__dict__: if B.__dict__[method] is None: return NotImplemented break else: return NotImplemented return True ``` This is an incredibly convenient function (referred to as check_methods here on out) for creating abstract base classes, and is much simpler than using `hasattr` for each method you want to check. For example: ``` >>> from abc import ABCMeta >>> # Without check_methods >>> class A(metaclass=ABCMeta): ... @classmethod ... def __subclasshook__(cls, subclass): ... return (hasattr(subclass, 'foo') and ... callable(subclass.foo) and ... hasattr(subclass, 'bar') and ... callable(subclass.bar) or ... NotImplemented) ... >>> # With check_methods >>> class B(metaclass=ABCMeta): ... @classmethod ... def __subclasshook(cls, subclass): ... return check_methods(subclass, 'foo', 'bar') ... >>> ``` This would be a great function to add to the standard lib, perhaps in the `abc` module. One problem with `check_methods` as defined in _collections_abc.py is that it doesn't check if the name is callable. Also, type hints and more readable variables may be desirable. The final code, if implemented, may look something like this: ``` # In imports section: from typing import Literal def check_methods(Class: type, *methods: str) -> Literal[True, NotImplemented]: """Check if class `Class` has methods `methods`.""" mro = Class.__mro__ for method in methods: for Base in mro: if (attr := getattr(Base, method, None)) is not None: if not callable(attr): return NotImplemented break else: return NotImplemented return True ``` Again, this would be a great function to add to the `abc` module or a similar one. ---------- components: Library (Lib) messages: 399814 nosy: finnjavier08 priority: normal severity: normal status: open title: Add check_methods function to standard library type: enhancement _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue44941> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com