What is the difference between these two python idioms?
if data is not None:
return data
if data: return data
asked Jun 14, 2013 at 21:10
Niklas Rosencrantz
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1See: stackoverflow.com/questions/6497166/… and stackoverflow.com/questions/26595/…Josh Lee– Josh Lee2013-06-14 21:26:12 +00:00Commented Jun 14, 2013 at 21:26
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1 Answer
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.
