从类内部方法更改全局变量 [英] Change global variables from inside class method

问题描述

当我尝试执行以下代码时，first_list会被修改，而第二个列表则不会发生任何变化.有没有一种方法可以将外部列表替换为全新的列表，或者只能从内部类方法中调用列表方法?我尝试在分配操作之前添加global关键字，但是会产生语法错误.

When I try to execute the code below, the first_list gets modified while no changes occur to the second one. Is there a way to replace an outside list with a brand new list, or calling list methods is the only thing I'm allowed to do from inside class methods? I tried adding global keyword before the assignment operation, but it produces a syntax error.

first_list = []
second_list = []


class MyClass:

    def change_values(self):
        first_list.append('cat')
        second_list = ['cat']

 test = MyClass()
 test.change_values()
 print(first_list)
 print(second_list)

推荐答案

第一:拥有具有可变状态的全局变量几乎是从不.您应该将模块级变量用作常量或单例.如果要更改变量的值，则应将其作为参数传递给函数，然后从函数返回新值.

First: It's almost NEVER a good idea to have global variables with mutable state. You should use module level variables just as constants or singletons. If you want to change a value of a variable you should pass it as a parameter to a function and then return a new value from a function.

说您的问题的答案将是:

Said that the answer to your question would be either:

first_list = []
second_list = []


class MyClass:
    def change_values(self):
        first_list.append('cat')
        second_list[:] = ['cat']

test = MyClass()
test.change_values()
print(first_list)
print(second_list)

或:

first_list = []
second_list = []


class MyClass:
    def change_values(self):
        first_list.append('cat')
        global second_list
        second_list = ['cat']

test = MyClass()
test.change_values()
print(first_list)
print(second_list)

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