example.py

In [1]: class Descr:
   ...:     def __init__(self):
   ...:         self.get_counter = 0
   ...: 
   ...:     def __get__(self, instance, owner):
   ...:         if instance is None:
   ...:             return self
   ...:         self.get_counter += 1
   ...:         return 1
   ...:     

In [2]: class Class:
   ...:     d = Descr()
   ...:     

In [3]: inst = Class()

In [4]: inst.__dict__
Out[4]: {}

In [5]: for n in range(10):
   ...:     inst.d
   ...:     

In [6]: Class.d.get_counter
Out[6]: 10

In [7]: inst.d = 2

In [8]: inst.__dict__
Out[8]: {'d': 2}

In [9]: for n in range(10):
   ...:     inst.d
   ...:     

In [10]: Class.d.get_counter
Out[10]: 10