有没有办法让 for-each 循环并行?

2022-01-24 00:00:00 python iteration parallel-processing foreach

问题描述

假设我在 Python 中有 2 个列表，我想并行遍历每个列表 - 例如对两个列表都使用元素 1，对两个列表使用元素 2……我知道我可以通过使用索引来做到这一点:

Let's say I have 2 lists in Python and I want to loop through each one in parallel - e.g. do something with element 1 for both lists, do something with element 2 for both lists... I know that I can do this by using an index:

for listIndex in range(len(list1)):
   doSomething(list1[listIndex])
   doSomething(list2[listIndex])

但是有没有办法通过 foreach 循环更直观地做到这一点?类似于 for list1Value in list1, list2Value in list2...?

But is there a way to do this more intuitively, with a foreach loop? Something like for list1Value in list1, list2Value in list2...?

我目前在 Python 中遇到过这种情况，但这是一个长期存在的问题，我很想知道您是否可以用任何语言做到这一点.(我只是假设 Python 最有可能有处理这个问题的方法.)

I've currently run into this situation in Python, but this is a longstanding question and I'd be interested to know if you can do this in any language. (I just assumed that Python is the most likely to have a method of dealing with this.)

解决方案

像这样?

for (a,b) in zip(list1, list2):
  doSomething(a)
  doSomething(b)

虽然如果 doSomething() 没有进行 I/O 或更新全局状态，并且它一次只对其中一个元素起作用，但顺序并不重要，所以你可以使用 chain()(来自 itertools):

Though if doSomething() isn't doing I/O or updating global state, and it just works on one of the elements at a time, the order doesn't matter so you could just use chain() (from itertools):

for x in chain(list1, list2):
  doSomething(x)

恰到好处，from itertools import * 是我经常做的事情.考虑使用 izip() 而不是使用我上面给出的 zip().另请查看izip_longest()、izip(count(), lst)等.欢迎使用函数式编程.:-)

Apropos, from itertools import * is something I do very often. Consider izip() instead of using the zip() I gave above. Also look into izip_longest(), izip(count(), lst), etc. Welcome to functional programming. :-)

哦，压缩也适用于更多列":

Oh, and zipping also works with more "columns":

for idx, a, b, c in izip(count(), A, B, C):
  ...

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