Python拼合列表(但并非始终如此) [英] Python flatten list (but not all the way)

问题描述

我有一个列表列表...

I have a list of lists of lists...

A = [ [[1,3]], [[3,5], [4,4], [[5,3]]] ]

以下函数输出[1, 3, 3, 5, 4, 4, 5, 3]

def flatten(a):
    b = []
    for c in a:
        if isinstance(c, list):
            b.extend(flatten(c))
        else:
            b.append(c)
    return b

但是，我想在最后一级停止展平，以便得到[ [1,3], [3,5], [4,4], [5,3] ]

However, I want to stop flattening on the last level so that I get [ [1,3], [3,5], [4,4], [5,3] ]

推荐答案

您可以在展平前测试包含的列表:

You could test for contained lists before flattening:

def flatten(a):
    b = []
    for c in a:
        if isinstance(c, list) and any(isinstance(i, list) for i in c):
            b.extend(flatten(c))
        else:
            b.append(c)
    return b

演示:

>>> def flatten(a):
...     b = []
...     for c in a:
...         if isinstance(c, list) and any(isinstance(i, list) for i in c):
...             b.extend(flatten(c))
...         else:
...             b.append(c)
...     return b
... 
>>> A = [ [[1,3]], [[3,5], [4,4], [[5,3]]] ]
>>> flatten(A)
[[1, 3], [3, 5], [4, 4], [5, 3]]

这试图在情况下尽可能高效； any()仅需要测试，直到找到列表为止，而不是所有元素.

This tries to be as efficient as can be under the circumstances; any() only needs to test until a list is found, not all elements.

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