CODEWITHSUNDEEP
python-2.7
Niklas Rosencrantz
Niklas Rosencrantz

Reputation: 26647

What is meant by "is not None" in python?

What is the difference between these two python idioms?

if data is not None: return data

if data: return data

Upvotes: 8

Views: 9237

Answers (1)

Josh Lee
Josh Lee

Reputation: 177584

The latter will also reject False, 0, [], (), {}, set(), '', and any other value whose __bool__ method returns False, including most empty collections.

The None value in Python is often used to indicate the lack of a value. It appears automatically when a function does not explicitly return a value.

>>> def f():
...   pass
>>> f() is None
True

It’s often used as the default value for optional parameters, as in:

def sort(key=None):
    if key is not None:
        # do something with the argument
    else:
        # argument was omitted

If you only used if key: here, then an argument which evaluated to false would not be considered. Explicitly comparing with is None is the correct idiom to make this check. See Truth Value Testing.

Upvotes: 16

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