How Can I Use A Static Method As A Default Parameter For The Strategy Design Pattern?

I want to make a class that uses a strategy design pattern similar to this: class C: @staticmethod def default_concrete_strategy(): print('default') @staticme

Solution 1:

No, you cannot, because the class definition has not yet completed running so the class name doesn't exist yet in the current namespace.

You can use the function object directly:

classC:    @staticmethoddefdefault_concrete_strategy():
        print("default")

    @staticmethoddefother_concrete_strategy():
        print("other")

    def__init__(self, strategy=default_concrete_strategy.__func__):
        self.strategy = strategy

C doesn't exist yet when the methods are being defined, so you refer to default_concrete_strategy by the local name. .__func__ unwraps the staticmethod descriptor to access the underlying original function (a staticmethod descriptor is not itself callable).

Another approach would be to use a sentinel default; None would work fine here since all normal values for strategy are static functions:

classC:    
    @staticmethoddefdefault_concrete_strategy():
        print("default")

    @staticmethoddefother_concrete_strategy():
        print("other")

    def__init__(self, strategy=None):
        if strategy isNone:
            strategy = self.default_concrete_strategy
        self.strategy = strategy

Since this retrieves default_concrete_strategy from self the descriptor protocol is invoked and the (unbound) function is returned by the staticmethod descriptor itself, well after the class definition has completed.