Python: Dynamically assign class methods

问题:

Essentially this is what I want to accomplish:

class Move(object):
    def __init__(self, Attr):
        if Attr:
            self.attr = Attr

        if hasattr(self, "attr"):
            __call__ = self.hasTheAttr
        else:
            __call__ = self.hasNoAttr

    def hasNoAttr(self):
        #no args!

    def hasTheAttr(func, arg1, arg2):
        #do things with the args

    __call__ = hasNoAttr

I know that that doesn't work, it just uses hasNoAttr all the time. My first thought was to use a decorator, but I'm not all that familiar with them and I couldn't figure out how to base it from whether or not a class attribute existed or not.

Actual question part: How would I be able to deterministically make a function either x function or y function depending on a condition.

回答1:

You can't really do this sort of thing with __call__ -- with other (non-magic) methods, you can just monkey-patch them, but with __call__ and other magic methods you need to delegate to the appropriate method within the magic method itself:

class Move(object):
    def __init__(self, Attr):
        if Attr:
            self.attr = Attr

        if hasattr(self, "attr"):
            self._func = self.hasTheAttr
        else:
            self._func = self.hasNoAttr

    def hasNoAttr(self):
        #no args!

    def hasTheAttr(func, arg1, arg2):
        #do things with the args

    def __call__(self,*args):
        return self._func(*args)