difference between 'if x not in dict' and 'if not x in dict'

Asked Jan 05 '17 at 00:06

Active Jan 05 '17 at 00:08

Viewed 223 times

I was testing some code where i wanted to print if x is in dictionary or not.

my code was

temp_dict = {...}
if x not in temp_dict:
    # Do something
    pass

However this didn't work, even though x wasn't present in temp_dict the if wasn't evaluated to True and its body wasn't executed (of course).

When I changed it to

temp_dict = {...}
if not x in temp_dict:
    # Do something
    pass

it worked!

Can somebody please explain the difference?

asked Jan 05 '17 at 00:06

pranav3688

2

There's no difference. You must have changed something else without noticing. – user2357112 Jan 05 '17 at 00:09
1

@JohnColeman `... not in ...` is valid in Python – vaultah Jan 05 '17 at 00:10
1

@JohnColeman: That would be true, except that Python actually has a `not in` operator that gets translated to a combination of `not` and `in`. – user2357112 Jan 05 '17 at 00:10
(In the bytecode, `not in` is its own opcode, and `not x in y` actually gets compiled to use the `not in` opcode, but in execution, the `not in` operator applies `in` and then `not`s the result.) – user2357112 Jan 05 '17 at 01:15
In what way did it "not work"? – Kevin J. Chase Jan 05 '17 at 01:52

0 Answers0