我可以为类而不是实例定义__repr__吗? [英] Can I define a __repr__ for a class rather than an instance?

问题描述

我可以为类而不是实例定义__repr__吗?例如，我正在尝试这样做

Can I define a __repr__ for a class rather than an instance? For example, I'm trying to do this

class A(object):
    @classmethod
    def __repr__(cls):
        return 'My class %s' % cls

我得到的是

In [58]: a=A()

In [59]: a
Out[59]: My class <class '__main__.A'>

In [60]: A
Out[60]: __main__.A

我试图使第60行的输出看起来像"My Class A"，而不是实例a.我想要这样做的原因是我正在使用Python的元类生成许多类.而且，与股票代表相比，我希望以一种更具可读性的方式来识别类别.

I'm trying to get the output of line 60 to look like "My Class A", not for the instance a. The reason I want to do this is I'm generating a lot of classes using Python's metaclass. And I want a more readable way to identify the class than the stock repr.

推荐答案

您需要在元类上定义__repr__.

class Meta(type):
    def __repr__(cls):
        return 'My class %s' % cls.__name__

class A(object):
    __metaclass__ = Meta

__repr__返回对象实例的表示.因此，通过在A上定义__repr__，可以指定想要repr(A())的外观.

__repr__ returns a representation of an instance of an object. So by defining __repr__ on A, you're specifying what you want repr(A()) to look like.

要定义类的表示形式，您需要定义如何表示type的实例.在这种情况下，请根据需要用定义为__repr__的自定义元类替换type.

To define the representation of the class, you need to define how an instance of type is represented. In this case, replace type with a custom metaclass with __repr__ defined as you need.

>> repr(A)
My class A

如果要为每个类定义一个自定义__repr__，我不确定是否有特别干净的方法.但是你可以做这样的事情.

If you want to define a custom __repr__ for each class, I'm not sure there's a particularly clean way to do it. But you could do something like this.

class Meta(type):
    def __repr__(cls):
        if hasattr(cls, '_class_repr'):
            return getattr(cls, '_class_repr')()
        else:
            return super(Meta, cls).__repr__()

class A(object):
    __metaclass__ = Meta

    @classmethod
    def _class_repr(cls):
        return 'My class %s' % cls.__name__

class B(object):
    __metaclass__ = Meta

然后，您可以按班级进行自定义.

Then you can customize on a per-class basis.

>> repr(A)
My class A
>> repr(B)
<__main__.B object at 0xb772068c>

这篇关于我可以为类而不是实例定义__repr__吗?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！