类和实例的方法相同 [英] The same method for class and instance

问题描述

我有 Books 类和 select 方法.还有一个名为 book 的类的实例.我希望能够同时执行 Books.select(where='...') 和 book.select(where='...'):>

I have class Books and method select in it. Also there is an instance of that class called book. I want to be able to do both Books.select(where='...') and book.select(where='...'):

class Books():
    def select(obj, where):
        print(obj, where)

book = Books()
Books.select(where='asdf')
book.select(where='asdf')

上面显然行不通，因为select是一个实例绑定方法:

The above obviously doesn't work, because select is an instance bound method:

Traceback (most recent call last):
  File "test.py", line 7, in <module>
    Books.select(where='asdf')
TypeError: select() takes exactly 2 arguments (1 given)

工作代码:

class Books():
    @staticmethod
    def select(obj, where):
        print(obj, where)

book = Books()
Books.select(Books, where='asdf')
Books.select(book, where='asdf')

我得到:

vic@wic:~/projects/snippets$ python3 test.py 
<class '__main__.Books'> asdf
<__main__.Books object at 0x17fd6d0> asdf

但我必须手动将类或其实例作为第一个参数传递给 select 方法 - 这不是我想要的.

But i have to manually pass the class or its instance as the first argument to the select method - not what i want.

如果我让 select 成为一个类方法:

If i make select a class method:

class Books():
    @classmethod
    def select(obj, where):
        print(obj, where)

book = Books()
Books.select(where='asdf')
book.select(where='asdf')

我总是把一个类作为第一个参数:

I always get a class as the first argument:

vic@wic:~/projects/snippets$ python3 test.py 
<class '__main__.Books'> asdf
<class '__main__.Books'> asdf

但我想在第二种情况下获得一个实例.

But i want to get an instance in the second case.

那么，有没有办法在不手动将类/实例作为第一个参数传递给静态方法的情况下完成我想要的?

So, is there a way to accomplish what i want without manually passing the class/instance as the first argument to a static method?

推荐答案

您可以使用 descriptor:

class Select(object):
    def __get__(self,obj,objtype):
        x=objtype if obj is None else obj
        def select(where):
            print(x,where)
        return select
class Books(object):
    select=Select()

book = Books()
Books.select(where='asdf')
book.select(where='asdf')

收益

<class '__main__.Books'> asdf
<__main__.Books object at 0xb7696dec> asdf

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