problem descriptors in Python

[akbarza]

hi
the below code is in address:
https://docs.python.org/3/howto/descriptor.html

import os

class DirectorySize:

    def __get__(self, obj, objtype=None):
        return len(os.listdir(obj.dirname))

class Directory:

    size = DirectorySize()              # Descriptor instance

    def __init__(self, dirname):
        self.dirname = dirname          # Regular instance attribute

s = Directory('songs')
g = Directory('games')
s.size                              # The songs directory has twenty files

g.size                              # The games directory has three files

os.remove('games/chess')            # Delete a game
g.size                              # File count is automatically updated

please note that you must change songs and games to two folders names in your system.
in the above address, it is quoted that:

Besides showing how descriptors can run computations, this example also reveals the purpose of the parameters to __get__(). The self parameter is size, an instance of DirectorySize. The obj parameter is either g or s, an instance of Directory. It is the obj parameter that lets the __get__() method learn the target directory. The objtype parameter is the class Directory.

how can I change the __get__ method to show(print at output) what is self and what is obj and what is objtype,namely for s=directory(..), output shows size and s and Directory

I read the first section of the above address, but I did not understand it. can you explain descriptors in Python?
thanks