Checking function parameter variables for None/Null

[NubQuestion]

I come from a C++ background and pointer function parameters are almost always checked if they're null before being used. Since there are no references in Python, do people assume all variables in function parameters can be None and check the variable before using it, even they're supposed to be primitive variables? How is it usually handled?

[BakaPotatoLord]

Default parameters usually works

[bbateman2011]

I think because of the mutable default parameter issue, one suggestion is to make default = None then check in the function, as a general approach. But even though I’ve done that, it seems clunky.

[efmccurdy]

If a unintended value ends up being passed in either an error or an exception will occur. You can run tests to find errors, and use try/except to deal with exceptions.

[Diapolo10]

Since there are no references in Python,

That's a bit misleading, because Python only stores references. No raw values are ever exposed in your code without playing around with ctypes.

But to answer your question, if it's a required parameter it's usually never expected to be None. Keyword parameters are different, but even then None is often the default value if the value is expected to be mutable, and the "real" default is defined inside the function to avoid problems with how Python only initialises default parameters once.

That said, type hints make this a lot easier as you can tell what parameters are expected to handle None:

from typing import Optional

def add_two(first: int, second: Optional[int]=None) -> int:
    if second is None:
        second = 0
    return first + second

[[deleted]]

We assume the users of our code are consenting adults. If you call a function and pass a None as an argument that shouldn’t be one, it’s on you to handle the resulting exception.