Not understood error with __set_name__ in a descriptor class
ast
ast at invalid
Sun Apr 19 11:14:13 EDT 2020
Le 19/04/2020 à 17:06, ast a écrit :
I understood where the problem is.
Once __get__ is defined, it is used to read self._name in method
__set_name__ and it is not défined yet. That's why I have
an error "'NoneType' object is not callable"
Thats a nice bug.
I need to think for a workaround
> 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
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