Why is subtraction faster than addition in Python?

Question

I was optimising some Python code, and tried the following experiment:

import time

start = time.clock()
x = 0
for i in range(10000000):
    x += 1
end = tim         


        

Answer 1

$ python -m timeit -s "x=0" "x+=1"
10000000 loops, best of 3: 0.151 usec per loop
$ python -m timeit -s "x=0" "x-=-1"
10000000 loops, best of 3: 0.154 usec per loop

Looks like you've some measurement bias