If in List vs For 循环(性能) [英] If in List vs For loop (performance)

问题描述

我很想知道 Python 中什么速度更快

I am curious to know what is faster in Python

说我有一个清单

myList = ['a', 'b', 'c', 'd', 'e']

我有两种方法可以检查一个项目是否在列表中.

I have two ways of checking if an item is in the list.

if item in myList:
    # doSomthing()

或

for element in myList:
    if element == item:
        # doSomething()

我知道第一种方法更pythonic"，但在性能方面有区别吗?

I know that the first method is more "pythonic" but in terms of performance is there a difference?

推荐答案

在 jupyter notebook 中测试，第一个选项对于字符串搜索明显更快:

Testing in jupyter notebook, the first option is significantly faster for a string search:

设置(来自这个问题):

rndm=''.join(choices(string.ascii_uppercase + string.digits, k=100000))

测试:

%timeit 'a' in rndm
26.2 µs ± 485 ns per loop

%%timeit 
for let in rndm: 
    if let=='a': 
        break
2.42 ms ± 73.7 µs per loop

注意:即使我们从 rndm 中创建一个 set() 并为搜索计时，它仍然只在 1.14 ms ± 26.9 µs per循环

Note: Even if we make a set() out of rndm and time the search, it still only comes in at 1.14 ms ± 26.9 µs per loop

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