什么是wrapper_descriptor，为什么在这种情况下Foo .__ init __()是一个? [英] What is a wrapper_descriptor, and why is Foo.__init__() one in this case?

问题描述

import inspect

class Foo(object):
    pass

if __name__ == '__main__':
    print type(Foo.__init__)
    print inspect.getsourcelines(Foo.__init__)

输出:

<type 'wrapper_descriptor'>
Traceback (most recent call last):
  *snip*
  File "/usr/lib/python2.7/inspect.py", line 420, in getfile
    'function, traceback, frame, or code object'.format(object))
TypeError: <slot wrapper '__init__' of 'object' objects> is not a module, class, method, function, traceback, frame, or code object

Google搜寻几乎没有提供有关wrapper_descriptor到底是什么的信息，以及为什么空类具有__init__方法而不是方法，而是一个wrapper_descriptor的有用信息.

Googling gives very little useful information about what, exactly, a wrapper_descriptor is, and why an empty class has an __init__ method that is not a method, but rather a wrapper_descriptor.

这到底是怎么回事?是否所有没有__init__方法的类都具有以下wrapper_descriptor之一?为什么在类字典中根本没有__init__?

What exactly is going on here? Do all classes without __init__ methods have one of these wrapper_descriptor things? Why is there an __init__ in the class dict at all?

推荐答案

您遇到的是实现细节.对于来说，这对于用C实现的类来说是非常典型的.它不是Python方法，而是C方法，包装器是此接口的一部分.

What you've run into is an implementation detail. This is pretty typical for classes implemented in C, as object is. It's not a Python method, it is a C method, and the wrapper is part of this interface.

为什么类字典中根本没有__init__?

它不在类字典中，而在object字典中. object具有__init__，因此当您尝试使用super()调用类的基类的__init__方法时，它不会失败.

It's not in the class dict, it's in the object dict. object has an __init__ so that when you try to call your class's base classes' __init__ methods using super(), it doesn't fail.

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