Why is any (True for ... if cond) much faster than any (cond for ...)?

Question

Two similar ways to check whether a list contains an odd number:

any(x % 2 for x in a) any(True for x in a if x % 2) 

Timing results with a = [0] * 10000000 (five attempts each, times in seconds):

0.60  0.60  0.60  0.61  0.63  any(x % 2 for x in a) 0.36  0.36  0.36  0.37  0.37  any(True for x in a if x % 2) 

Why is the second way almost twice as fast?

My testing code:

from timeit import repeat  setup = 'a = [0] * 10000000'  expressions = [     'any(x % 2 for x in a)',     'any(True for x in a if x % 2)', ]  for expression in expressions:     times = sorted(repeat(expression, setup, number=1))     print(*('%.2f ' % t for t in times), expression) 

Try it online!

Answer 1

The first method sends everything to any() whilst the second only sends to any() when there's an odd number, so any() has fewer elements to go through.