Re: Python constructors have particular semantics, and ‘Foo.__init__’ doesn't qualify

Terry Reedy tjreedy at udel.edu
Thu Dec 15 13:05:31 EST 2016


On 12/14/2016 11:14 PM, Thomas 'PointedEars' Lahn wrote:

> According to <https://docs.python.org/3/tutorial/classes.html#method-objects>, “Foo.__init__” is _not_ an instance method.  Were it an instance
> method, the following would not happen:

This link points to subsection 9.3.4. Method Objects

> | >>> class Foo:
> | ...     def __init__ (self):
> | ...         pass
> | ...
> | >>> Foo.__init__.__self__
> | Traceback (most recent call last):
> |   File "<stdin>", line 1, in <module>
> | AttributeError: 'function' object has no attribute '__self__'

You have misread the docs.  Foo.__init__ is the function. 
Foo().__init__ is a method object with the attribute __self__.  You 
omitted the ()s.

 >>> class C:
	def __init__(self): pass

	
 >>> ci = C().__init__
 >>> ci.__self__
<__main__.C object at 0x000001E38A750E80>

> Because “Instance method objects have attributes, too: m.__self__ is the
> instance object with the method m() […]”.

This line is from section 9.7. Odds and Ends. In this quote, 'm' is a 
method object, the result of 'instance.method, not a function.  In 
Python 2, 'm' would have been called a 'bound method', as opposed to an 
unbound method.  Since the latter were eliminated in 3.x, the adjective 
is no longer needed.



-- 
Terry Jan Reedy




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