如何在python中创建独立集列表？ [重复]

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I have a list that needs to contain a variable number of independent sets. When I run the following piece of code, I want to add the string "testing" to only the first set.

我有一个列表，需要包含可变数量的独立集。当我运行以下代码时，我想将字符串“testing”添加到第一组。

numberOfSets = 3    
test = [set()]*numberOfSets
test[0].add("testing")
print test

However, when I print test, it shows three identical sets that all contain testing. How can I set up my list so I can separately access each set?

但是，当我打印测试时，它会显示三个完全包含测试的相同集合。如何设置列表以便我可以单独访问每个设置？

2 个解决方案

#1

When you do [set()]*3, you create three sets that reference the same object, thus when you change one value, the others change. Use a list comprehension here instead:

当您执行[set（）] * 3时，您将创建三个引用同一对象的集合，因此当您更改一个值时，其他值会更改。改为使用列表推导：

>>> numberOfSets = 3   
>>> test = [set() for _ in xrange(numberOfSets)]
>>> test[0].add("testing")
>>> print test
[set(['testing']), set([]), set([])]

#2

You can do

你可以做

test = [set() for _ in xrange(numberOfSets)]  # use 'range' in Python 3.x

[set()]*x creates a list with x of the same set instance, whereas the comprehension above creates a new, independent set on each iteration, as desired.

[set（）] * x创建一个包含相同set实例的x的列表，而上面的解释根据需要在每次迭代时创建一个新的独立集合。

In general, you should be very cautious whenever you multiply lists whose elements are mutable.

通常，每当您将元素可变的列表相乘时，您应该非常谨慎。

#1