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 = ??
    ...

Possible duplicate of Python: Assign Value if None Exists

rnevius
– rnevius

2016-01-13 23:44:26 +00:00
Commented Jan 13, 2016 at 23:44 — rnevius
– rnevius, Commented Jan 13, 2016 at 23:44

Geotob · Accepted Answer · 2017-04-17 21:58:59Z

9

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.

edited Apr 17, 2017 at 21:58

answered Jan 13, 2016 at 23:48

Geotob

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Busturdust · Accepted Answer · 2016-01-13 23:51:28Z

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

answered Jan 13, 2016 at 23:51

Busturdust

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Comments

arainone · Accepted Answer · 2016-01-14 00:02:18Z

0

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

edited Jan 14, 2016 at 0:02

answered Jan 13, 2016 at 23:50

arainone

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