有条件的 Python 循环

Question

函数 f 将进行不必要的迭代。

def f(array):
    for (i, row) in enumerate(array):
        for (j, value) in enumerate(row):
            if i < some_number and j > some_other_number:
                do_something

是否有一种惯用的方法来在 for 循环中强制执行条件？

def f(array):
    for (i < some_number, row) in enumerate(array):
        for (j > some_other_number, value) in enumerate(row):
            do_something

Answer 1

您可以使用 itertools.islice(iterable,start,stop[,step])为此:

<b>from itertools import islice</b>

def f(array):
    for (i, row) in <b>islice(</b>enumerate(array)<b>,some_number)</b>:
        for (j, value) in <b>islice(</b>enumerate(row)<b>,some_other_number+1,None)</b>:
            # do_something
            pass

鉴于您在计算中不需要 i 和 j(您只需要它们进行边界检查，您甚至可以省略它们)。

from itertools import islice

def f(array):
    for row in islice(array,some_number):
        for value in islice(row,some_other_number+1,None):
            # do_something
            pass