为什么any（）比in这么快？

Question

https://repl.it/@ArmanTavakoli/List-Comprehension-vs-Any

Why is my any check so much faster than my in check when they are essentially doing the same thing?

from timeit import default_timer as timer
import random

input = [random.randint(0, 100) for x in range(0, 1000000)]

def any_check(input):
  return any(i == 1 for i in input)

def list_comprehension(input):
  return 1 in [num for num in input]

first_start = timer()
any_check(input)
first_end = timer()
print('any_check', first_end - first_start)

second_start = timer()
list_comprehension(input)
second_end = timer()
print('list_comprehension', second_end - second_start)

Results of running the functions 3 times each.

# Calculated with 3 runs each
# Ratio is list_comprehension:any_check

# 10,000 - Mean Ratio: 17.87
# Example run;
# any_check 1.5022000297904015e-05
# list_comprehension 0.00038980199315119535

# 100,000 - Mean Ratio: 140.76
# any_check 2.020499960053712e-05
# list_comprehension 0.0035961729954578914

# 1,000,000 - Mean Ratio: 3379.81
# any_check 2.2904998331796378e-05
# list_comprehension 0.08528400499926647

Answer 1

As several people pointed out in comments, the reason your function doing an in test is slower than the version using any is because that function also includes an unnecessary list comprehension that needs to iterate over the whole input before the in operator can begin looking for a match. When run on lists, both in and any can short circuit, quitting early if a matching value is found early in the search. But the list comprehension in your second function always iterates over the whole input even if there was a 1 right at the start.

If you replaced 1 in [num for num in input] with 1 in input , you'd see performance as good or better than in your function using any . Performance would be fairly similar if input was a list, but might be much faster for other container types (such as set s and range s).