Python if not == vs if !=

Question

What is the difference between these two lines of code:

if not x == \'val\':

and

if x != \'val\':

Is one

Answer 1

>>> from dis import dis
>>> dis(compile('not 10 == 20', '', 'exec'))
  1           0 LOAD_CONST               0 (10)
              3 LOAD_CONST               1 (20)
              6 COMPARE_OP               2 (==)
              9 UNARY_NOT
             10 POP_TOP
             11 LOAD_CONST               2 (None)
             14 RETURN_VALUE
>>> dis(compile('10 != 20', '', 'exec'))
  1           0 LOAD_CONST               0 (10)
              3 LOAD_CONST               1 (20)
              6 COMPARE_OP               3 (!=)
              9 POP_TOP
             10 LOAD_CONST               2 (None)
             13 RETURN_VALUE

Here you can see that not x == y has one more instruction than x != y. So the performance difference will be very small in most cases unless you are doing millions of comparisons and even then this will likely not be the cause of a bottleneck.