debugproperty.py

amirouche@neitram:~/tmp$ cat debugproperty.py
from traceback import print_stack
from weakref import WeakKeyDictionary


class DebugProperty:

    def __init__(self, name):
        self.name = name
        self.data = WeakKeyDictionary()

    def __get__(self, instance, owner):
        print('Property {} of {} accessed at:'.format(self.name, instance))
        print_stack()
        return self.data[instance]

    def __set__(self, instance, value):
        print('Property {} of {} changed to {} at:'.format(self.name, value, instance))
        print_stack()
        self.data[instance] = value


class VeryComplicatedClass:

    _very_important_value = DebugProperty('_very_important_value')
    
    def __init__(self, value):
        self._very_important_value = value


def test_traceback(my_object):
    my_object._very_important_value = 42
    return my_object._very_important_value


my_object = VeryComplicatedClass(101)


out = test_traceback(my_object)

assert out == 42
amirouche@neitram:~/tmp$ python3 debugproperty.py 
Property _very_important_value of 101 changed to <__main__.VeryComplicatedClass object at 0x7fbab0fd4128> at:
  File "debugproperty.py", line 35, in <module>
    my_object = VeryComplicatedClass(101)
  File "debugproperty.py", line 27, in __init__
    self._very_important_value = value
  File "debugproperty.py", line 18, in __set__
    print_stack()
Property _very_important_value of 42 changed to <__main__.VeryComplicatedClass object at 0x7fbab0fd4128> at:
  File "debugproperty.py", line 38, in <module>
    out = test_traceback(my_object)
  File "debugproperty.py", line 31, in test_traceback
    my_object._very_important_value = 42
  File "debugproperty.py", line 18, in __set__
    print_stack()
Property _very_important_value of <__main__.VeryComplicatedClass object at 0x7fbab0fd4128> accessed at:
  File "debugproperty.py", line 38, in <module>
    out = test_traceback(my_object)
  File "debugproperty.py", line 32, in test_traceback
    return my_object._very_important_value
  File "debugproperty.py", line 13, in __get__
    print_stack()