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Description
patch decorator is a little bit problematic when working with abstract classes,
consider the following code:
fromabcimportABC,abstractmethodfromfastcore.basicsimportpatchclassA(ABC):@abstractmethoddeffoo(self):passclassB(A):def__init__(self):pass@patchdeffoo(self :B):print("foo patched to B")a=B()Executingthecodeyieldsthiserror:
TypeError:Can'tinstantiateabstractclassBwithabstractmethodsfoo
The reason for that problem is that in Python each class that is inheriting from an abstract class he starts with an attribute calledabstractmethods which is a frozenset that contains a set of functions that should be implemented by the child class, this attribute gets updated only in the scope of the class definition and at the end the set should be empty i.e the child class has implemented all the abstractmethods, since we are using patch to separate functions into different cells, Python doesn't see that we actually implemented the required functions.
possible solution, that's the decorator that we used in our code (you can learn from it what you should do to fix on your end):
defpatch_method(func :Callable,*args,**kwargs)->None:""" Applies fastcore's `patch` decorator and removes `func` from `cls.__abstractsmethods__` in case <br> `func` is an `abstractmethods` """cls=next(iter(get_type_hints(func).values()))try:abstracts_needed=set(cls.__abstractmethods__)abstracts_needed.discard(func.__name__)cls.__abstractmethods__=abstracts_neededexceptAttributeError:# If the class does not inherit from an abstract classpassfinally:# Apply the original `patch` decoratorpatch(*args,**kwargs)(func)