Python:使用用户输入作为类名的类工厂 [英] Python: Class factory using user input as class names

问题描述

我想动态地将类属性添加到超类.此外，我想动态创建从该超类继承的类，这些子类的名称应取决于用户的输入.

I want to add class atttributes to a superclass dynamically. Furthermore, I want to create classes that inherit from this superclass dynamically, and the name of those subclasses should depend on user input.

有一个超类"Unit"，我可以在运行时向其添加属性.这已经有效.

There is a superclass "Unit", to which I can add attributes at runtime. This already works.

def add_attr (cls, name, value):
    setattr(cls, name, value)

class Unit(object):
    pass

class Archer(Unit):
    pass

myArcher = Archer()
add_attr(Unit, 'strength', 5)
print "Strenght ofmyarcher: " + str(myArcher.strength)
Unit.strength = 2
print "Strenght ofmyarcher: " + str(myArcher.strength)

这将导致所需的输出:
myarcher的实力:5
myarcher的优势:2

This leads to the desired output:
Strenght ofmyarcher: 5
Strenght ofmyarcher: 2

但是现在我不想预定义Archer子类，而是让用户决定如何调用此子类.我已经尝试过这样的事情:

But now I don't want to predefine the subclass Archer, but I'd rather let the user decide how to call this subclass. I've tried something like this:

class Meta(type, subclassname):
    def __new__(cls, subclassname, bases, dct):
    return type.__new__(cls, subclassname, Unit, dct)

factory = Meta()    
factory.__new__("Soldier")  

但是没有运气.我想我还不太了解新在这里的功能. 因此，我想要的是

but no luck. I guess I haven't really understood what new does here. What I want as a result here is

class Soldier(Unit):
    pass

由工厂创建.如果我用"Knight"作为参数来调用工厂，我想创建一个Unit类的Knight子类.

being created by the factory. And if I call the factory with the argument "Knight", I'd like a class Knight, subclass of Unit, to be created.

有什么想法吗?提前非常感谢！
再见
-萨诺

Any ideas? Many thanks in advance!
Bye
-Sano

推荐答案

要从名称创建类，请使用class语句并分配名称.观察:

To create a class from a name, use the class statement and assign the name. Observe:

def meta(name):
    class cls(Unit):
        pass

    cls.__name__ = name
    return cls

现在我想我应该解释一下自己，依此类推.使用class语句创建类时，它是动态完成的-等效于调用 type() .

Now I suppose I should explain myself, and so on. When you create a class using the class statement, it is done dynamically-- it is equivalent of calling type().

例如，以下两个片段执行相同的操作:

For example, the following two snippets do the same thing:

class X(object): pass
X = type("X", (object,), {})

类的名称-类型的第一个参数-分配给__name__，这基本上就是结束(仅在默认的__repr__()实现中使用__name__本身是唯一的时间).要创建一个具有动态名称的类，实际上您可以像这样调用类型，或者您也可以随后更改类名称.但是，class语法的存在是有原因的-它很方便，以后添加和更改内容也很容易.例如，如果您想添加方法，

The name of a class-- the first argument to type-- is assigned to __name__, and that's basically the end of that (the only time __name__ is itself used is probably in the default __repr__() implementation). To create a class with a dynamic name, you can in fact call type like so, or you can just change the class name afterward. The class syntax exists for a reason, though-- it's convenient, and it's easy to add to and change things later. If you wanted to add methods, for example, it would be

class X(object):
    def foo(self): print "foo"

def foo(self): print "foo"
X = type("X", (object,), {'foo':foo})

，依此类推.因此，我建议您使用class语句-如果您从一开始就知道可以这样做，那么您很可能会这样做.处理type等等都是一团糟.

and so on. So I would advise using the class statement-- if you had known you could do so from the beginning, you likely would have done so. Dealing with type and so on is a mess.

(顺便说一句，您不应手动呼叫type.__new__()，而只能呼叫type())

(You should not, by the way, call type.__new__() by hand, only type())

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