descriptors #1

function_to_method.py

def a(self):
    return self

# write, and optionally modify class A in a way where the following will work
inst = A()
print(inst.sub.a() is inst)  # True

# ------------------------------------- instance methods through class binding

# if there were no subspace, this would just work:
class A:
    pass

A.a = a
# we are trying to duplicate the things that are happening under the hood here
# as a bonus, the binding happens on class level, so we don't need an __init__

# -------------------------------------------------- Aran Fey's ProxyNamespace

class ProxyNamespace:
    def __init__(self, **attrs):
        self._attrs = attrs
    
    def __get__(self, inst, owner):
        return Proxy(self._attrs, inst)

class Proxy:
    def __init__(self, namespace, this):
        self.__namespace = namespace
        self.__this = this
    
    def __getattr__(self, attr):
        obj = self.__namespace[attr]
        
        if hasattr(obj, '__get__'):
            obj = obj.__get__(self.__this, type(self.__this))
        
        return obj

class A:
    sub = ProxyNamespace(a=a)

# ---------------------------------------------- using MethodType and __init__

from types import SimpleNamespace, MethodType

class A:
    def __init__(self):
        self.sub = SimpleNamespace('a'=MethodType(a, self))