Python列出理解 [英] Python lists comprehension

问题描述

string = "Hello 12345 World"
numbers = [x for x in string if x.isdigit()]
print numbers

>> ['1', '2', '3', '4', '5']

另一个例子:

>>> noprimes = [j for i in range(2, 8) for j in range(i*2, 50, i)]
>>> primes = [x for x in range(2, 50) if x not in noprimes]
>>> print primes
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

让我感到困惑的是x for x部分.我之前已经看过几个地方，但不确定它的含义.有人可以提供更多示例并为这些示例提供解释吗?

What is confusing me is the x for x part. I've seen it a few places before but unsure what it means. Could someone provide more examples and explanation for these examples?

推荐答案

这些结构称为列表理解.

简单示例

[x for x in iterable]的字面意思是对于可迭代的每个元素，将该元素添加到新创建的列表中".等同于

[x for x in iterable] literally means "for every element in iterable, add that element to newly created list" and is equivalent to

new_list = []
for x in iterable:
    new_list.append(x)

逐行说明:

Loop                             List comprehension
--------------------------------------------------------------------------
new_list = []                    [x for x in iterable]
for x in iterable:               [x for x in iterable]
    new_list.append(x)           [x for x in iterable]

更复杂的示例

[int(x) for x in string if x.isdigit()]可以理解为对于可迭代的每个元素，如果将x.isdigit()应用于元素，则将对新创建的列表应用int的结果相加".

[int(x) for x in string if x.isdigit()] can be read as "for every element in iterable, add the result of applying int to the element to newly created list if x.isdigit()".

逐行说明:

Loop                             List comprehension
-------------------------------------------------------------------------
numbers = []                     [int(x) for x in string if x.isdigit()]
for x in string:                 [int(x) for x in string if x.isdigit()]
    if x.isdigit():              [int(x) for x in string if x.isdigit()]
        numbers.append(int(x))   [int(x) for x in string if x.isdigit()]

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