Python魔法增强任务误解 [英] Python Magic Method Augmented Assignment misunderstanding

问题描述

我创建一个简单的角度对象，它是最简单的形式，当它超过360（回0）或低于0（回到360）时重现的整数值。我实现了增强的任务的魔法方法，并且由于某种原因这不工作。

  class Angle：
 
 def __init __（self，angle）：
 self.angle = angle 
 
 def __add __（self，other）：
检查递归，然后返回添加值。
 val = self.angle + other 
 while val> 360：
 val  -  = 360 
 while val< 0：
 val + = 360 
 return val 
 
 def __radd __（self，other）：
反映的加法。 self .__ add __（other）
 
 def __iadd __（self，other）：
增加的加法赋值。
 val = self .__ add __ $ b self.angle = val 
  

它将一个非类型的值赋给self.angle，=。它似乎应该工作，因为 self .__ add __（）返回其他添加到self.angle的值，所以为什么不会分配<$ c $

关于 __ iadd __ code>（和其他 __ iXXX __ 方法）：

尝试在原地进行操作（修改
self）并返回结果（可以是但不一定是
self）。

您的 __ iadd __ 方法不会将非类型指派给 .angle ，它返回 None （当函数没有显式返回时的默认值），并且将当前名称重新绑定到 None ，即：

  class Foo（object）：
 def __init __ self，angle = 120）：
 self.angle = angle 
 
 def __add __（self，other）：
检查递归，然后返回添加的值。 
 printFoo.add
 val = self.angle + other 
 while val> 360：
 val  -  = 360 
 while val< 0：
 val + = 360 
 return val 
 
 
 def __iadd __（self，other）：
增加的加法赋值。 
 printFoo.iadd
 val = self .__ add __（other）
 self.angle = val 
 
 
f = Foo bf + = 20 
 
 print f is None 
  

short：你想要 __ iadd __ 返回有意义的，很可能 self 。

I'm creating a simple angle object which is, in it's simplest forms, an integer value that recurs when it goes above 360 (back to 0) or below 0 (back to 360). I implemented the magic methods for augmented assignment and for some reason this isn't working.

class Angle:

    def __init__(self, angle):
    self.angle = angle

    def __add__(self, other):
        """Check for recursion, then return the added value."""
        val = self.angle + other
        while val > 360:
            val -= 360
        while val < 0:
            val += 360
        return val

    def __radd__(self, other):
        """Reflected addition."""
        return self.__add__(other)

    def __iadd__(self, other):
        """Augmented addition assignment."""
        val = self.__add__(other)
        self.angle = val

It assigns a nonetype value to self.angle,=. It seems to me like it should work, since self.__add__() returns the value of other added to self.angle, so why wouldn't it assign val to self.angle?

解决方案

About __iadd__ (and other __iXXX__ methods):

These methods should attempt to do the operation in-place (modifying self) and return the result (which could be, but does not have to be, self).

Your __iadd__ method doesn't "assigns a nonetype to self.angle", it returns None (default value when a function has no explicit return), and this rebinds your current name to None, ie:

class Foo(object):
    def __init__(self, angle=120):
        self.angle = angle

    def __add__(self, other):
        """Check for recursion, then return the added value."""
        print "Foo.add"
        val = self.angle + other
        while val > 360:
            val -= 360
        while val < 0:
            val += 360
        return val


    def __iadd__(self, other):
        """Augmented addition assignment."""
        print "Foo.iadd"
        val = self.__add__(other)
        self.angle = val


f = Foo()
f += 20

print f is None

To make a long story short : you want __iadd__ to return something meaningfull, most probably self.

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