自动函数调用Python类的实例变量？ [英] Automatic function call on instance variable of Python class?

问题描述

 <$ c $  
 c> class Car（object）：
汽车以重量和速度为例。
 def __init __（self）：
 self.weight = None 
 self。速度=无
  

如果我初始化一个 Car 作为空对象：

  red_car = Car（）
  

我添加了一个速度和一个权重： p>

  red_car.speed = 60 
 red_car.weight = 3500 
  

这很好，但如果我想在试图将这些变量添加到实例时运行一个函数呢？像这个函数：

  def change_weight（self，any_int）：
 return（any_int  -  10）
  

虽然我希望它在我尝试将特定实例变量添加到对象时自动运行此函数。如果可能，我希望它只在权重实例变量上运行 change_weight 。

我是否正确理解这个问题，或者我应该单独通过函数运行整数，然后手动添加到对象中？

解决方案

你想使用属性

  class Car（object）：
 
 def __init __（self）：
 self._weight = None＃内部值
 self.speed =无
 
 @财产
 def weight（self）：
 return self._weight 
 
 @ weight.setter 
 def weight（self，the_weight）：
 self._weight = the_weight  -  10＃or any here 
  

现在，您可以设置 speed 通常;当你执行 car.weight = 20 时，setter函数将被调用，实际重量将被设置为 20 - 10 = 10 。

So lets say I have a class called Car as below:

class Car(object):
    """Car example with weight and speed."""
    def __init__(self):
        self.weight = None
        self.speed = None

If I initialize a Car as an empty object:

red_car = Car()

And I add a speed and a weight:

red_car.speed = 60
red_car.weight = 3500

That's all fine but what if I want to run a function when attempting to add those variables to the instance? Like this function:

def change_weight(self, any_int):
    return (any_int - 10)

The thing is though I want it to automatically run this function whenever I attempt to add specific instance variables to the object. If possible I would like it to run change_weight only on the weight instance variable.

Am I understanding this correctly or should I just be running the integer through the function separately and then adding to the object after manually?

解决方案

You want to use properties

class Car(object):
    """Car example with weight and speed."""
    def __init__(self):
        self._weight = None # internal value
        self.speed = None

    @property
    def weight(self):
        return self._weight

    @weight.setter
    def weight(self, the_weight):
        self._weight = the_weight - 10 # or whatever here

Now, you can set speed normally; when you execute car.weight = 20 the setter function will be called, and the actual weight will be set to 20 - 10 = 10.

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