如何并行遍历两个列表?

In Python 2, zip returns a list of tuples. This is fine when foo and bar are not massive. If they are both massive then forming zip(foo,bar) is an unnecessarily massive temporary variable, and should be replaced by itertools.izip or itertools.izip_longest, which returns an iterator instead of a list.

import itertools
for f,b in itertools.izip(foo,bar):
    print(f,b)
for f,b in itertools.izip_longest(foo,bar):
    print(f,b)

izip 在 foo 或 bar 用尽时停止.当 foo 和 bar 都用尽时，izip_longest 停止.当较短的迭代器用尽时，izip_longest 会产生一个元组，其中 None 在对应于该迭代器的位置.您还可以根据需要设置除 None 之外的其他 fillvalue.查看全文.

izip stops when either foo or bar is exhausted. izip_longest stops when both foo and bar are exhausted. When the shorter iterator(s) are exhausted, izip_longest yields a tuple with None in the position corresponding to that iterator. You can also set a different fillvalue besides None if you wish. See here for the full story.

还要注意 zip 及其类似 zip 的 brethen 可以接受任意数量的可迭代对象作为参数.例如，

Note also that zip and its zip-like brethen can accept an arbitrary number of iterables as arguments. For example,

for num, cheese, color in zip([1,2,3], ['manchego', 'stilton', 'brie'], 
                              ['red', 'blue', 'green']):
    print('{} {} {}'.format(num, color, cheese))

打印

1 red manchego
2 blue stilton
3 green brie

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