python 3：类“模板” （返回参数化类的函数） [英] python 3: class "template" (function that returns a parameterized class)

问题描述

我试图创建一个传递参数 x 并返回新类 C 的函数。 C 应该是固定基类 A 的子类，仅添加一个：添加特定的类属性，然后设置为等于 x 。

I am trying to create a function that is passed a parameter x and returns a new class C. C should be a subclass of a fixed base class A, with only one addition: a certain class attribute is added and is set to equal x.

换句话说：

class C(A):
  C.p = x # x is the parameter passed to the factory function

这容易做到吗？我应该注意什么问题吗？

Is this easy to do? Are there any issues I should be aware of?

推荐答案

首先，请注意，类工厂一词在某些情况下已过时蟒蛇。它用于C ++之类的语言中，用于返回动态类型的类实例的函数。它之所以命名，是因为它在C ++中脱颖而出。虽然这种情况并不罕见，但是它并不常见，因此给模式命名很有用。但是，在Python中，这是不断进行的操作-这是一项基本操作，没有人再为它起一个特殊的名字。

First off, note that the term "class factory" is somewhat obsolete in Python. It's used in languages like C++, for a function that returns a dynamically-typed instance of a class. It has a name because it stands out in C++; it's not rare, but it's uncommon enough that it's useful to give the pattern a name. In Python, however, this is done constantly--it's such a basic operation that nobody bothers giving it a special name anymore.

此外，请注意，类工厂返回实例一个类-不是类本身。 （同样，这是因为它来自C ++之类的语言，它们没有返回类的概念，而只是返回对象。）但是，您说过要返回新类，而不是类的新实例。

Also, note that a class factory returns instances of a class--not a class itself. (Again, that's because it's from languages like C++, which have no concept of returning a class--only objects.) However, you said you want to return "a new class", not a new instance of a class.

创建本地类并返回它很简单：

It's trivial to create a local class and return it:

def make_class(x):
    class C(A):
        p = x
    return C

这篇关于python 3：类“模板” （返回参数化类的函数）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！