Search notes:
Python: descriptor
A
descriptor is an
object that defines at least one of the
dunders __get__,
__set__ or
__delete__.
class desc:
def __get__(self, obj, objtype):
print('__get__ was called, obj.ident =', obj.ident)
return self.val
def __set__(self, obj, val):
print('__set__ was called, obj.ident =', obj.ident)
self.val = val
def __delete__(self, obj):
print('__delete__ was called, obj.ident =', obj.ident)
class CLS:
#
# Note: D (the descriptor object) is a class
# variable, not an instance variable:
#
D = desc()
def __init__(self, ident):
self.ident = ident
obj_a = CLS('A')
obj_b = CLS('B')
obj_a.D = 42
#
# __set__ was called, obj.ident = A(
obj_b.D = 99
#
# __set__ was called, obj.ident = B
val_a = obj_a.D
#
# __get__ was called, obj.ident = A
val_b = obj_b.D
#
# __get__ was called, obj.ident = B
print(val_a)
#
# 99
print(val_b)
#
# 99
del obj_a.D
#
# __delete__ was called, obj.ident = A