Python optional parameters

Question

Guys, I just started python recently and get confused with the optional parameters, say I have the program like this:

class B:
   pass

class A:
    def __in         


        

Answer 1

you need to do the following:

class A:
    def __init__(self, builds=None):
        if builds is None:
            builds = B()
        self.builds = builds

it's a very wide-spread error, using mutable parameters as a default arguments. there are plenty of dupes probably on SO.