Python 'If not' syntax


Question

I'm a bit confused about how/why so many python developers use if not in their conditional statements.

for example, lets say we had a function,

def foo(bar = None):
    if not bar:
        bar = 2

But why go about this way? I mean, wouldn't doing if bar != None or if bar is not Nonebe more explicit? What does if not try to say?

1
138
5/24/2013 4:24:03 PM

Accepted Answer

Yes, if bar is not None is more explicit, and thus better, assuming it is indeed what you want. That's not always the case, there are subtle differences: if not bar: will execute if bar is any kind of zero or empty container, or False. Many people do use not bar where they really do mean bar is not None.

176
5/24/2013 4:29:35 PM

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