编写列表理解以拼合嵌套列表 [英] Writing a list comprehension to flatten a nested list

问题描述

我有一个包含列表和数字的嵌套列表.

I have a nested list mixed with list and numbers.

nested = [[1, 2, 3], [4, 5, 6], [7, 8], [9], 10, 11]

嵌套列表仅包含数字，而永远不会包含更多列表.

The nested lists only contain numbers, they'll never contain more lists.

是否可以编写列表理解以从嵌套"列表中创建新列表，并产生以下输出?

Is it possible to write a list comprehension to make new list from the 'nested' list, producing the following output?

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

这是我的尝试(代码不起作用)

This was my attempt( code is not working)

[num if isinstance(item, list) for num in item else item for item in nested]

推荐答案

您需要将实例测试放入循环中，以便可以从嵌套列表中提取元素:

You need to put your instance test in a loop, so you can extract the elements from a nested list:

[num for item in nested for num in (item if isinstance(item, list) else (item,))]

演示:

>>> nested = nested = [[1, 2, 3], [4, 5, 6], [7, 8], [9], 10, 11]
>>> [num for item in nested for num in (item if isinstance(item, list) else (item,))]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

如果您首先将其表示为一组for循环，则将有所帮助；您的尝试基本上是这样做的:

It helps if you first express this as a set of for loops; your attempt essentially did this:

for item in nested:
    _element = num if isinstance(item, list) for num in item else item
    result.append(_element)

这不是真正有效的Python.

which is not really valid Python.

我上面的列表理解是这样做的:

My list comprehension above instead does this:

for item in nested:
    _iterable = item if isinstance(item, list) else (item,)
    for num in _iterable:
        _element = num
        result.append(_element)

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