I am trying to have a single static variable as an 'id' for all the child instantiations of this parent class. The problem I'm having is double counting of this ID, likely because the parent's __init__ gets called twice. But if I remove the explicit Parent().__init__() call, then the counter doesn't get incremented at all. How do I get the id to increment only ones? Here's my code snippet:
#!/usr/bin/python3
class Parent:
cls_id = 0
def __init__ (cls):
cls.cls_inc_id()
@classmethod
def cls_inc_id (cls):
cls.cls_id += 1
@classmethod
def child_inc_id (self):
self.id += 1
class Child1 (Parent):
def __init__ (self):
Parent().__init__()
self.id = super().cls_id
print ("Child1 id: ", self.id)
class Child2 (Parent):
def __init__ (self):
Parent().__init__()
self.id = super().cls_id
print ("Child2 id: ", self.id)
child1 = Child1()
child2 = Child1()
child3 = Child2()
child4 = Child2()
My output is: %> ./static_vars.py
Child1 id: 2
Child1 id: 4
Child2 id: 6
Child2 id: 8
Thanks in advance
As others have mentioned, you're not using super constructor correctly, but also I would reference the actual class in the parent class, not the instance self which you incorrectly named cls:
class Parent:
cls_id = 0
def __init__(self):
self.id = Parent.cls_id
Parent.cls_id += 1
class Child1(Parent):
def __init__(self):
super().__init__()
print ("Child1 id: ", self.id)
class Child2(Parent):
def __init__(self):
super().__init__()
print ("Child2 id: ", self.id)
child1 = Child1()
child2 = Child1()
child3 = Child2()
child4 = Child2()
Child1 id: 0
Child1 id: 1
Child2 id: 2
Child2 id: 3
If you wanted a separate ID per type of class, you could use a dictionary mapping class to id:
from collections import defaultdict
class Parent:
cls_ids = defaultdict(int)
def __init__(self):
self.id = Parent.cls_ids[type(self)]
Parent.cls_ids[type(self)] += 1
Child1 id: 0
Child1 id: 1
Child2 id: 0
Child2 id: 1