My question is related to bound method object, more specifically I am trying to imitate the same behavior that functions (which are essentially descriptors) present.
Let me first put here my understanding of how class_instance.function() works
class D(object):
def dfunc(self):
...
d=D()
d.dfunc() # will call D.__dict__['dfunc'].__get__(d,D)()
# gives a bound method which can be used directly
a=D.__dict__['dfunc'].__get__(d,D)
a() # works as d.D()
Does Python call D.__dict__['dfunc'] (d)
, in case when type(dfunc)
is function and type(d).__dict__['dfunc'].__get__(d, type(d))
if x is a class instance?
Now coming to how I am trying to create a bound object using closure:
class E(object):
def __get__(self,obj,cls):
def returned(*args):
print(obj.__dict__)
return returned
class F(object):
e = E()
y = 9
f = F()
f.fvar = 9 # putting something in instances __dict__
a = f.e # will call the __get__ function of F and return a closure
a() # works and produces instance specific result -> {'fvar': 9}, just like a bound method
Now the main question,
when I did a = D.__dict__['dfunc'].__get__(d,D)
type(a) was bound method, but when I implement it type(a)
is function; is there a way to return bound object from user-defined descriptor?
Is there any better way to implement a function like descriptor? Please correct me if I have gotten something fundamentally incorrect in my head.
If you want to return a method instead, you can create one from the function object together with the arguments passed to __get__
:
import types
class E(object):
def __get__(self,obj,cls):
def returned(*args):
print(obj.__dict__)
return types.MethodType(returned, obj, cls)
However, it's not totally clear what this gains you. If just returning a function already works, why do you need it to be a "real" method?