Hello This code is working well: (I am using python 3.6.3)
-------------------------------------------------------------------- class my_property: def __init__(self, fget=None, fset=None, fdel=None): self.fget = fget self.fset = fset self.fdel = fdel def __set_name__(self, owner, name): self._name = name print("Inside __set_name__ method: ", self._name) ## def __get__(self, instance, owner): ## return self.fget(instance) class Test: celsius = my_property() print("Outside __set_name__ method: ", Test.celsius._name) Here is the output: ========= RESTART: C:/Users/jm/Desktop/python/my_property.py ========= Inside __set_name__ method: celsius Outside __set_name__ method: celsius -------------------------------------------------------------------- And this one doesn't. (I just removed ## to uncomment the 2 lines) Do you understand why ? class my_property: def __init__(self, fget=None, fset=None, fdel=None): self.fget = fget self.fset = fset self.fdel = fdel def __set_name__(self, owner, name): self._name = name print("Inside __set_name__ method: ", self._name) def __get__(self, instance, owner): return self.fget(instance) class Test: celsius = my_property() print("Outside __set_name__ method: ", Test.celsius._name) Here is the output: ========= RESTART: C:/Users/jm/Desktop/python/my_property.py ========= Inside __set_name__ method: celsius Traceback (most recent call last): File "C:/Users/jm/Desktop/python/my_property.py", line 17, in <module> print("Outside __set_name__ method: ", Test.celsius._name) File "C:/Users/jm/Desktop/python/my_property.py", line 11, in __get__ return self.fget(instance) TypeError: 'NoneType' object is not callable -- https://mail.python.org/mailman/listinfo/python-list