Difference between "if x" and "if x is not None"
x = 0
if x: ... # False
if x is not None: ... # True
In the following cases:
test = False
test = ""
test = 0
test = 0.0
test = []
test = ()
test = {}
test = set()
the if
test will differ:
if test: #False
if test is not None: #True
This is the case because is
tests for identity, meaning
test is not None
is equivalent to
id(test) == id(None) #False
therefore
(test is not None) is (id(test) != id(None)) #True
The former tests trueness, whereas the latter tests for identity with None
. Lots of values are false, such as False
, 0
, ''
, and None
, but only None
is None
.