Question

If we have a class with a few default arguments set to None, how do we ignore them if they are None, and use them if they are not (or at least one of them is not None)?

class Foo:
def __init__(self, first=1, second=2, third=3, fourth=None, fifth=None):
    self.first = first
    self.second = second
    self.third = third
    self.fourth = fourth
    self.fifth = fifth
    self.sum = self.first + self.second + self.third + self.fourth + self.fifth
    return self.sum

>>> c = Foo()
Traceback (most recent call last):
File "<pyshell#120>", line 1, in <module>
c = Foo()
File "<pyshell#119>", line 8, in __init__
self.sum = self.first + self.second + self.third + self.fourth + self.fifth
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

Answer 1

def __init__(self, first=1, second=2, third=3, fourth=None, fifth=None):
    if first is None:
        first = 0
    else:
        self.first = first

Then it will add zero with no side effects instead of None

You could also change the part where you add them up and test for None first but this is probably less typing.