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

I think the "general programming lesson" is that it is really hard to predict, solely by looking at the source code, which sequence of statements will be the fastest. Programmers at all levels frequently get caught up by this sort of "intuitive" optimisation. What you think you know may not necessarily be true.

There is simply no substitute for actually measuring your program performance. Kudos for doing so; answering why undoubtedly requires delving deep into the implementation of Python, in this case.

With byte-compiled languages such as Java, Python, and .NET, it is not even sufficient to measure performance on just one machine. Differences between VM versions, native code translation implementations, CPU-specific optimisations, and so on will make this sort of question ever more tricky to answer.