How do you create an incremental ID in a Python Class

Question

I would like to create a unique ID for each object I created - here's the class:

class resource_cl :
    def __init__(self, Name, Position, Type, Active):
        self.Name = Name
        self.Position = Position
        self.Type = Type
        self.Active = Active

I would like to have a self.ID that auto increments everytime I create a new reference to the class, such as:

resources = []
resources.append(resource_cl('Sam Sneed', 'Programmer', 'full time', True))

I know I can reference resource_cl, but I'm not sure how to proceed from there...

Answer 1

First, use Uppercase Names for Classes. lowercase names for attributes.

class Resource( object ):
    class_counter= 0
    def __init__(self, name, position, type, active):
        self.name = name
        self.position = position
        self.type = type
        self.active = active
        self.id= Resource.class_counter
        Resource.class_counter += 1

Answer 2

Using count from itertools is great for this:

>>> import itertools
>>> counter = itertools.count()
>>> a = next(counter)
>>> print a
0
>>> print next(counter)
1
>>> print next(counter)
2
>>> class A(object):
...   id_generator = itertools.count(100) # first generated is 100
...   def __init__(self):
...     self.id = next(self.id_generator)
>>> objs = [A(), A()]
>>> print objs[0].id, objs[1].id
100 101
>>> print next(counter) # each instance is independent
3

The same interface works if you later need to change how the values are generated, you just change the definition of id_generator.

Answer 3

Are you aware of the id function in python, and could you use it instead of your counter idea?

class C(): pass

x = C()
y = C()
print id(x), id(y)    #(4400352, 16982704)

Answer 4

Concise and elegant:

import itertools

class resource_cl():
    newid = itertools.count().next
    def __init__(self):
        self.id = resource_cl.newid()
        ...