避免 if else 实例化一个类 - python [英] Avoid if else to instantiate a class - python

问题描述

我想根据字段的值创建一个类的对象.

I want to create an object of a class based on value of a field.

例如:

if r_type == 'abc':
                return Abc()
            elif r_type == 'def':
                return Def()
            elif r_type == 'ghi':
                return Ghi()
            elif r_type == 'jkl':
                return Jkl()

在这里避免if else的pythonic方法是什么.我正在考虑创建一个字典，其中 r_type 是键，类名是值，然后获取值并实例化，这是一种正确的方法，还是在 python 中有更好的惯用方法?

What is a pythonic way to avoid if else here. I was thinking to create a dictionary with r_type being key and classname being value, and do a get of the value and instantiate, is it a proper way, or there is something better idiomatic way in python?

推荐答案

您可以利用类第一类对象，并使用字典访问你要创建的类:

You can take advantage of the fact that classes are first class objects in python, and use a dictionary to access the classes you want to create:

classes = {'abc': Abc,    # note: you store the object here
           'def': Def,    #       do not add the calling parenthesis
           'ghi': Ghi,
           'jkl': Jkl}

然后像这样创建类:

new_class = classes[r_type]()  # note: add parenthesis to call the object retreived

如果您的类需要参数，您可以像在正常的类创建中一样放置它们:

If your classes require parameters, you can place them like in normal class creation:

new_class = classes[r_type](*args, *kwargs)

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