python Python在子列表中查找列表长度
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/2031846/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Python find list lengths in a sublist
提问by JBWhitmore
I am trying to find out how to get the length of every list that is held within a particular list. For example:
我试图找出如何获取特定列表中包含的每个列表的长度。例如：
a = []
a.append([])
a[0].append([1,2,3,4,5])
a[0].append([1,2,3,4])
a[0].append([1,2,3])
I'd like to run a command like:
我想运行如下命令：
len(a[0][:])
which would output the answer I want which is a list of the lengths [5,4,3]. That command obviously does not work, and neither do a few others that I've tried. Please help!
这将输出我想要的答案，即长度 [5,4,3] 的列表。该命令显然不起作用，我尝试过的其他一些命令也不起作用。请帮忙！
回答by sberry
[len(x) for x in a[0]]?
[len(x) for x in a[0]]?
>>> a = []
>>> a.append([])
>>> a[0].append([1,2,3,4,5])
>>> a[0].append([1,2,3,4])
>>> a[0].append([1,2,3])
>>> [len(x) for x in a[0]]
[5, 4, 3]
回答by Matthew Iselin
map(len, a[0])
map(len, a[0])
回答by John Machin
[len(x) for x in a[0]]
回答by T. Stone
This is known as List comprehension(click for more info and a description).
这被称为列表理解（单击以获取更多信息和描述）。
[len(l) for l in a[0]]
回答by Alex Martelli
def lens(listoflists):
return [len(x) for x in listoflists]
now, just call lens(a[0])instead of your desired len(a[0][:])(you can, if you insist, add that redundant [:], but that's just doing a copy for no purpose whatsoever -- waste not, want not;-).
现在，只需调用lens(a[0])而不是你想要的len(a[0][:])（如果你坚持，你可以添加那个多余的[:]，但这只是无缘无故地复制——不要浪费，不要；-）。
回答by ghostdog74
using the usual "old school" way
使用通常的“老派”方式
t=[]
for item in a[0]:
t.append(len(item))
print t
回答by divenex
Matthew's answer does not work in Python 3. The following one works in both Python 2 and Python 3
马修的答案在 Python 3 中不起作用。以下一个在 Python 2 和 Python 3 中都有效
list(map(len, a[0]))
list(map(len, a[0]))
