Calling methods without objects?

[Steve D'Aprano]

On Tue, 26 Sep 2017 08:49 am, Stefan Ram wrote:

>   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?

Indeed there is.

Methods (like functions) are first-class values in Python, so you can do:

py> finder = "Hello World!".find
py> finder("W")
6


We say that `finder` is a bound method, meaning that it is a method object that
already knows the instance to operate on.

Python also has unbound methods: method objects that don't know the instance to
operate on, and so the caller has to provide it:

py> unbound_finder = str.find
py> unbound_finder("Goodbye for now", "f")
8


In Python 2, both bound and unbound methods were implemented as the same
underlying type, namely a thin wrapper around a function. In Python 3, unbound
methods no longer use the wrapper, and just return the function object itself.

The wrapper can be found in the types module:

from types import MethodType



-- 
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.