将基类转换为派生类python（或更多pythonic方法的扩展类） [英] Cast base class to derived class python (or more pythonic way of extending classes)

问题描述

我需要扩展Networkx python包并为我的特殊需要添加一些方法到 Graph 类

I need to extend the Networkx python package and add a few methods to the Graph class for my particular need

我想这样做的方法是简单地派出一个新类说 NewGraph ，并添加所需的方法。

The way I thought about doing this is simplying deriving a new class say NewGraph, and adding the required methods.

然而，networkx中有几个其他函数可以创建并返回 Graph 对象（例如生成一个随机图）。我现在需要将这些 Graph 对象转换为 NewGraph 对象，以便我可以使用我的新方法。

However there are several other functions in networkx which create and return Graph objects (e.g. generate a random graph). I now need to turn these Graph objects into NewGraph objects so that I can use my new methods.

这样做的最佳方式是什么？或者我应该以完全不同的方式解决问题？

What is the best way of doing this? Or should I be tackling the problem in a completely different manner?

推荐答案

如果您只是添加行为，而不是依赖于额外的实例值，你可以从数学中分配给对象的 __ class __ ：

If you are just adding behavior, and not depending on additional instance values, you can assign to the object's __class__:

from math import pi

class Circle(object):
    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return pi * self.radius**2

class CirclePlus(Circle):
    def diameter(self):
        return self.radius*2

    def circumference(self):
        return self.radius*2*pi

c = Circle(10)
print c.radius
print c.area()
print repr(c)

c.__class__ = CirclePlus
print c.diameter()
print c.circumference()
print repr(c)

打印：

10
314.159265359
<__main__.Circle object at 0x00A0E270>
20
62.8318530718
<__main__.CirclePlus object at 0x00A0E270>

这与Python中的cast接近，就像在C中投射一样如果不考虑这个问题就不可能做到。我发布了一个相当有限的示例，但如果您可以保持在约束范围内（只是添加行为，没有新的实例变量），那么这可能有助于解决您的问题。

This is as close to a "cast" as you can get in Python, and like casting in C, it is not to be done without giving the matter some thought. I've posted a fairly limited example, but if you can stay within the constraints (just add behavior, no new instance vars), then this might help address your problem.

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