Nathan Kirui :
As per definition, the None keyword is used to define a null value, or no value at all. But why does:
inputs = [3, 0, 1, 2, None]
print(list(filter(None, inputs)))
return this list [3,1,2] and not [3,0,1,2]?
jonrsharpe :
Per the filter docs:
If function is
None, the identity function is assumed, that is, all elements of iterable that are false are removed.
The identity function is basically:
def identity(something):
return something
so filtering on this means that any value that evaluates false-y will be excluded from the output.
Then if you look at truth-value testing you can see that, as well as None, 0 evaluates false-y in Python:
Here are most of the built-in objects considered false:
- constants defined to be false:
NoneandFalse.- zero of any numeric type:
0,0.0,0j,Decimal(0),Fraction(0, 1)- ...
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