Set instance variable as default parameter to class function

Question

I have a class function that takes 4 arguments, all class member variables in practice. Usually only one of these arguments is modified at a time and the rest of the time the would-be defaults (current values of the class member variables) are passed to the function/written out even though they aren't changing.

I thought the best would be to make these class member variables the defaults, but I'm having a hard time getting the best syntax. The following code produces behavior I desire - using a class member variable as a default parameter to a function. But it's ugly:

class test:
    def __init__(self, a, b):
        self.a = a
        self.b = b

    def testfunc(self, param = None):
        if not param:
            param = self.a
        print(param)


if __name__ == '__main__':
    a1 = test(1, 3)
    a1.testfunc()
    a2 = test(5, 5)
    a2.testfunc()
   #(prints 1 and 5 when called)

I would like to use the following:

    def testfunc(self, param = self.a):
        print(param)

But this gives the error:

NameError: name 'self' is not defined

What's a better way to do this?

Answer 1

Your first attempt is pythonic, the only thing I would change is the test:

 def testfunc(self, param = None):
        if param is None:
            param = self.a
        print(param)

The problem with testing for False is that zero and an empty container (including an empty string) all resolve to False.

If you have a large number of these, see Understanding kwargs in Python