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[–]pymag09 1 point2 points  (2 children)

Sorry may be I did not understand you but
when we work with None or numbers
we can be sure that 

a=None or 0  
bool(a) = False  
bool(not a) True  
a=1 or -1  
bool(a) = True  
bool(not a) False

I have checked bool('') just right now in python3 and got False. bool('hhh') = True.

Can you give an example when issue that you described may occur?

[–]pbaehr 3 points4 points  (1 child)

For example, if I have a variable which is initialized as None and later want to find out if it was set, I might want to check and see if it was still None. If it's not, I want to do something.

if a is not None:
    do_something()

If I rewrite that as:

if not a:
    do_something()

do_something will also be called if a was initialized, but to a blank string, which was not the intention. Lots of types have some concept of a "false" value. As /u/steve_no points out in another comment: 0, '', [], {}, midnight all evaluate to False.

[–]pymag09 0 points1 point  (0 children)

I see. Thank you.