如何检查列表中的元素是否为列表(在Python中)?

If we have the following list:

如果我们有以下清单:

list = ['UMM', 'Uma', ['Ulaster','Ulter']]

If I need to find out if an element in the list is itself a list, what can I replace aValidList in the following code with?

如果我需要找出列表中的元素是否本身就是一个列表，我可以用以下代码替换aValidList吗?

for e in list:
    if e == aValidList:
        return True

Is there a special import to use? Is there a best way of checking if a variable/element is a list?

是否有特殊的导入要使用?是否有最好的方法检查变量/元素是否是列表?

3 个解决方案

#1

Use isinstance:

使用isinstance:

if isinstance(e, list):

If you want to check that an object is a list or a tuple, pass several classes to isinstance:

如果要检查对象是list或tuple，请将几个类传递给isinstance:

if isinstance(e, (list, tuple)):

#2

1. Work out what specific properties of a list you want the items to have. Do they need to be indexable? Sliceable? Do they need an .append() method?

   计算出你想要的条目的具体属性。它们需要可索引吗?切割的?他们需要一个.append()方法吗?

2. Look up the abstract base class which describes that particular type in the collections module.

   查找描述集合模块中特定类型的抽象基类。

3. Use isinstance:

   使用isinstance:

   isinstance(x, collections.MutableSequence)
   

---

You might ask "why not just use type(x) == list?" You shouldn't do that, because then you won't support things that look like lists. And part of the Python mentality is duck typing:

您可能会问“为什么不使用type(x) = list?”你不应该这样做，因为那样你就不会支持看起来像列表的东西。Python思维的一部分是鸭子类型:

I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck

我看见一只鸟像鸭子一样走路，像鸭子一样游泳，像鸭子一样嘎嘎叫，我把那只鸟叫做鸭子

In other words, you shouldn't require that the objects are lists, just that they have the methods you will need. The collections module provides a bunch of abstract base classes, which are a bit like Java interfaces. Any type that is an instance of collections.Sequence, for example, will support indexing.

换句话说，您不应该要求对象是列表，只是要求它们具有您需要的方法。collections模块提供了一组抽象基类，有点类似于Java接口。集合实例的任何类型。例如，序列将支持索引。

#3

Expression you are looking for may be:

你正在寻找的表达可能是:

...
return any( isinstance(e, list) for e in my_list )

Testing:

测试:

>>> my_list = [1,2]
>>> any( isinstance(e, list) for e in my_list )
False
>>> my_list = [1,2, [3,4,5]]
>>> any( isinstance(e, list) for e in my_list )
True
>>>