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

In the first one Python has to execute one more operations than necessary(instead of just checking not equal to it has to check if it is not true that it is equal, thus one more operation). It would be impossible to tell the difference from one execution, but if run many times, the second would be more efficient. Overall I would use the second one, but mathematically they are the same