Python - what does ' obj.__n = 3 ' do in this code?

Question

class Myclass:
def __init__(self, n=1):
self.__n = n
def val_n(self):
return self.__n

obj = Myclass("zzz")
print(obj.val_n()) # outputs zzz

obj.__n = 3 # What does this do?
print(obj.__n) # outputs 3 as expected
print(obj.val_n()) # outputs zzz

1) What does obj.__n = 3 do to the class? It doesn't seem to affect the value of the n attribute...
2) Why do we need the double underscore before the n in self.__n?

Answer 1

A double underscore prefix causes the Python interpreter to rewrite the attribute name in order to avoid naming conflicts in subclasses.

1)obj.__n does not refferering to Myclass.__n. But it creating a new variable.
see this by comment
#obj. __n = 3
print(obj.__n) is error now.
2) for naming conflicts in subclasses... It is not accessible out of class..

Answer 2

Jayakrishna🇮🇳

I see, so obj.__n = 3 does NOT mean assigning 4 to self.__n = n.
Rather, obj.__n = 3 is a new variable outside of the class.

I'm still a bit confused about the dot in obj.__n.
Is obj.__n the name of an integer variable?
--> why does it contain a dot/period?

From my understanding, a variable name CANNOT contain a period...

Answer 3

(ohh.. I just now seen this post)

obj.__n here obj is object created for class Myclass by statement
obj = Myclass("zzz")
This calls Myclass constructor and creates a object and stored in obj.
now with this obj, you can call that class methods and data properties by period operator like obj.n means reffering the data value n of object
obj.val_n() means calling val_n() method of obj object...
The period is called derefferncing operator..