How to set a default parameter of a class member function as another member function within the same class in Python

Question

What I want to do is: Pass foo function pointer to function bar as a default parameter. But it is not allowed. How to implement it?

class Klass ():
    def __init__(self):
        print('init')

    def foo(self):
        print('foo')

    def bar(self, func=self.foo): # error here
        func()
        print('bar')

Function pointer? Python doesn't have function pointers. In any case, the problem is `self` isn't defined. Just use `foo`. — juanpa.arrivillaga, Aug 07 '19 at 17:46
You can't do it. The default value is evaluated when the function is defined, not when it's called. — Barmar, Aug 07 '19 at 17:46

score 4 · Accepted Answer · answered Aug 07 '19 at 17:48

The default value is evaluated once, when the function is defined, not every time it's called. So it can't refer to other parameters or other dynamic data.

You'll need to assign it in the function.

def bar(self, func = None):
    if func is None:
        func = self.foo
    func()
    print('bar')

How to set a default parameter of a class member function as another member function within the same class in Python

1 Answers1