问题

我是新手使用Python中的面向对象编程（OOP），也是新手总体来说，我想知道更改对象变量的正确方法。由于Python不能返回"void"，所以当对象变量发生更改时，我需要返回一些东西。

```python
class classA:
   var_a = 1
   var_b = 1

def changeSomething(classAObj):
    classAObj.var_a = 2
    return classAObj

def main():
    classAObj = classA()
    changeSomething(classAObj)
    .....在这里使用具有新更改的对象.....

在changeSomething函数中，将整个classAObj返回是否正确？还是只返回变量，即

...
return classAobj.var_a

无论哪种方式，我都能获得相同的结果，classAObj.var_a都发生了变化，但正确的做法是什么？

<details>
<summary>英文:</summary>

Im new to OOP in Python (and in general) and wondering about the correct way to change object variables. Since Python cant return void i need to return something when an object variable has changed.

class classA:
var_a = 1
var_b = 1

def changeSomething(classAObj):
classAObj.var_a = 2
return classAobj

def main()
classAObj = classA()
changeSomething(classAObj)
.....use object with new changes here....

Is it correct to return the entire classAObj in the changeSomething function? Or should i only return the variable i.e 

...
return classAobj.var_a

I get the same result in either way, classAObj.var_a has changed in both cases, but what is the correct way to do it?

</details>


# 答案1
**得分**: 0

`changeSomething` 不应该返回*任何东西*；当它直接修改参数时，应该隐式地返回`None`。只有那些生成新修改*副本*的函数应该返回它们（并保持参数不被修改）。

所以你的代码应该是这样的：

```python
class classA:
   def __init__(self):
       self.var_a = 1  # 这里忘了加self
       self.var_b = 1  # 这里忘了加self

def changeSomething(classAObj):
    classAObj.var_a = 2  # 修复名称，self不会存在，你可以通过不同的名称接收它

def main():
    classAObj = classA()
    changeSomething(classAObj)  # classAObj在原地修改，所以在调用者看到的是更改
    # .....在这里使用具有新更改的对象.....

或者，考虑到这是一个类，将changeSomething作为实例方法更有意义，例如：

class classA:
   def __init__(self):
       self.var_a = 1  # 这里忘了加self
       self.var_b = 1  # 这里忘了加self

    # 缩进以将其设置为类的方法
    def changeSomething(self):  # 参数重命名以符合实例方法的标准命名
        self.var_a = 2

def main():
    classAObj = classA()
    classAObj.changeSomething()  # 使用方法调用语法，classAObj仍在原地修改
    # .....在这里使用具有新更改的对象.....

class classA:
   def __init__(self):
       self.var_a = 1  # You forget self here
       self.var_b = 1  # You forget self here

def changeSomething(classAObj):
    classAObj.var_a = 2  # Fix name, self wouldn't exist, you received it by a different name

def main():
    classAObj = classA()
    changeSomething(classAObj)  # classAObj is modified in place, so changes seen in caller
    # .....use object with new changes here....

class classA:
   def __init__(self):
       self.var_a = 1  # You forget self here
       self.var_b = 1  # You forget self here

    # Indented to make it a method of the class
    def changeSomething(self):  # Argument renamed to follow standard naming for instance methods
        self.var_a = 2

def main():
    classAObj = classA()
    classAObj.changeSomething()  # Use method call syntax, classAObj still modified in place
    # .....use object with new changes here....