清单&的Python奇怪行为附加 [英] Python Strange Behavior with List & Append

问题描述

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.代码下面是我的预期输出和实际输出.最后要注意的一点是，我理解这段代码可能是奇怪的"，至少可以说使用range(1)有点奇怪.这样做的原因是程序中的这种确切出现(范围是变量，但处于这些值)会导致问题..所以我制作了此简单的代码来复制它.

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)

预期产量

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

实际输出

['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

我感谢您解释为什么会这样.我不确定内置的append()函数是否会以某种方式影响所有用户，或者每个用户是否以某种方式共享其字段.在Python 2.7.3上运行.

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.

推荐答案

将此与您的代码进行比较

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')

请注意，没有必要在类级别声明"任何变量

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

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