Python奇怪的行为与列表和追加(Python Strange Behavior with List & Append)

以下代码是我遇到的问题，正在寻找解释。代码的行为与我预期的不同。下面的代码将是我的预期输出和实际输出。最后要注意的是，我知道这个代码可能是'奇怪的'，使用范围（1）有点奇怪，至少可以说。原因是程序中的这种确切发生（范围是变量，但是在这些值）引起了问题..所以我让这个简单的代码来复制它。

userList = [] class User(): listA = [] listB = [] def setup(self): for i in range(1): self.listA.append('a') self.listB.append('b') for i in range(5): user = User() userList.append(user) for i in range(len(userList)): userList[i].setup() for i in range(len(userList)): print str(userList[i].listA) print str(userList[i].listB)

预期产出

['a'] ['b'] ['a'] ['b'] ['a'] ['b'] ['a'] ['b'] ['a'] ['b']

实际产出

['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b']

讨论

我很感激为什么会发生这种情况的任何解释。我不确定内置的append（）函数是以何种方式影响所有用户，或者如果每个用户以某种方式共享他们的字段。在Python 2.7.3上运行。

The following code is an issue I encountered and am looking for an explanation. The behavior of the code different than what I expected. Below the code will be my expected output, and the actual output. One last thing to note, is that I understand this code may be 'strange', and that using range(1) is a bit odd to say the least. The reason for this is that this exact occurrence in a program (the ranges were variables but at these values) caused problems.. so I made this simple code to replicate it.

userList = [] class User(): listA = [] listB = [] def setup(self): for i in range(1): self.listA.append('a') self.listB.append('b') for i in range(5): user = User() userList.append(user) for i in range(len(userList)): userList[i].setup() for i in range(len(userList)): print str(userList[i].listA) print str(userList[i].listB)

Expected Output

['a'] ['b'] ['a'] ['b'] ['a'] ['b'] ['a'] ['b'] ['a'] ['b']

Actual Output

['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b'] ['a','a','a','a','a'] ['b','b','b','b','b']

Discussion

I appreciate any explanation as to why this is happening. I'm not sure if the built-in append() function is somehow affecting all Users, or if each User is somehow sharing their fields. Running on Python 2.7.3.

最满意答案

将此与您的代码进行比较

class User(): def setup(self): self.listA = [] # instance variable self.listB = [] # instance variable for i in range(1): self.listA.append('a') self.listB.append('b')

请注意，没有必要在课堂级别“声明”任何变量

Compare this to your code

class User(): def setup(self): self.listA = [] # instance variable self.listB = [] # instance variable for i in range(1): self.listA.append('a') self.listB.append('b')

Note that it's not necessary to "declare" any variables at the class level

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