One liner Python equivalent of JavaScript like assignment when value is falsey

Question

Consider a function in JavaScript:
If val is not defined in the first call, it becomes 0

function someRecursiveFn (item, val) {
    val = val || 0;
    ...
}

How do I assign the same way in Python?

def someRecursiveFn(item, val):
    val = ??
    ...

Answer 1

You could use a keyword argument instead of a plain argument to your function:

def someRecursiveFn(item, val=None):
    val = val or 0

so val will default to None if it's not passed to the function call.

the val = val or 0 will ensure that val=None or val='' are converted to 0. Can be omitted if you only care about val being defined in the first place.

Answer 2

val = val if val else 0

#if val is not None, it will assign itself, if it is None it will set val=0

Answer 3

This:

def someRecursiveFn(item, val):
    val = val if val else 0

But the python idiom if val is quite broad as it can have different meanings, some of them could even mean something in a specific context(for example the 0 value), contrarily to an undefined value in javascript.

In python, all the following are considered false:

• None
• False
• zero of any numeric type, for example, 0, 0L, 0.0, 0j.
• any empty sequence, for example, '', (), [].
• any empty mapping, for example, {}.
• instances of user-defined classes, if the class defines a nonzero() or len() method, when that method returns the integer zero or bool value False