Difference between “if x” and “if x is not None”

Question

It appears that \"if x\" is almost like short-hand for the longer \"if x is not None\" syntax. Are they functionally identical or are there cases where for a given value of

Answer 1

if x checks if x is considered as True.

In Python, everything has a boolean value (True/False).

Values that are considered as False:

• False, None
• 0, 0.0, 0j
• [], (), {}
• ''
• Other instances that signal to Python that they are empty

Other values are considered as True. For example, [False], ('hello'), 'hello' are considered as True (because they are not empty).

When using if x is not None, you are checking if x is not None, but it can be False or other instances that are considered as False.

>>> x = None
>>> if not x:print x # bool(None) is False
None
>>> if x == None:print x
None
>>> x = False
>>> if not x:print x
False
>>> if x == None:print x

Finally, note that True and False are respectively equal to 1 and 0:

>>> True + 1
2
>>> False + 1
1
>>> range(1, 5)[False]
1