I tried using timeit and time.clock() but my computer's speed is inconsistent and I couldn't find out which is faster, If this question already exists then I apologize but I couldn't find it.
Testing %2 (i.e. for oddness / evenness) can be performed quickly by examining the least significant bit of a number. (Do that with logical AND: (n & 1)). You'd be hard pressed to beat that.
But any potential performance gain might be probably attenuated in Python, so profile it and use if only, in your judgement, the performance gain outweighs the obfuscating effects of an expression which, although idiomatic in C and C++, may well be unfamiliar to folk with whom you are collaborating.
What is faster? "5 % 2 == 0" or "not 5 % 2"