Re: Calling methods without objects?

2017-09-26 Thread Stephan Houben 
Op 2017-09-25, Stefan Ram schreef :

>   So, is there some mechanism in Python that can bind a method
>   to an object so that the caller does not have to specify the
>   object in the call?
>
>   If so, how is this mechanism called?
>

Others have already explained the details how functions become bound
methods, but I would just point out that it is an instance of a piece of
very general functionality: the descriptor protocol.

https://docs.python.org/3.6/howto/descriptor.html

With this, you can create your own objects which do some arbitrary
special thing when accesses on an instance.

Stephan
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Re: Calling methods without objects?

2017-09-26 Thread Gregory Ewing 

Thomas Jollans wrote:

When an object is
constructed from a class, all functions in the class are turned into
method objects that refer back to the original object.


That's not quite true. Nothing is done to the methods at
the time an instance is created; rather, a bound method
object is created each time a method is looked up via
an instance.

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Re: Calling methods without objects?

2017-09-25 Thread Thomas Jollans 
On 26/09/17 01:04, Thomas Jollans wrote:
>
> In [1]: class C:
>
>...: def m(self):
>
>...: return True
I'll have to give my MUA a stern talking to about the importance of
whitespace. Anyway, you know what I mean.
>
>...:

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Re: Calling methods without objects?

2017-09-25 Thread Chris Angelico 
On Tue, Sep 26, 2017 at 8:49 AM, Stefan Ram  wrote:
> |>>> from random import randint
> |
> |>>> randint
> |>
> |
> |>>> randint.__self__
> |
> |
> |>>> randint( 2, 3 )
> |2
>
>   It seems I am calling the method »randint« of the object at
>   »0x389798«, but I do not have to write the object into the
>   call!?
>
>   So, is there some mechanism in Python that can bind a method
>   to an object so that the caller does not have to specify the
>   object in the call?
>
>   If so, how is this mechanism called?

>>> stuff = []
>>> add_stuff = stuff.append
>>> add_stuff("spam")
>>> add_stuff("eggs")
>>> add_stuff("sausage")
>>> add_stuff("spam")
>>> stuff
['spam', 'eggs', 'sausage', 'spam']

In a typical method call, "obj.meth(args)", the "obj.meth" part is
itself a valid expression, and it evaluates to a bound method object.
I suppose you could call that mechanism "method binding" if you like,
but mainly it's just attribute lookup.

ChrisA
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