CODEWITHSUNDEEP
pythonpython-3.x
A_Worthy
A_Worthy

Reputation: 65

ID function issues

So I am supposed to create a class that has A unique ID for each object (starts at 0). It should also automatically assign it a unique ID every time a new object is created. Hints (The constructor of the class should automatically assign the ID of the Geometry object. The data type of the ID is an integer and starts at 0) My output is supposed to resemble

>>>geo1 = Geometry()
>>>geo1.id
0
>>>geo2 = Geometry()
>>>geo2.id
1

My issue is id seems to be a built in function that generates a random number. But my instructions say the number is supposed to start a 0. Is there anyway to make that happen?

My code

class Geometry (object):

    def __init__(geo, id):
        geo.id = geo1
geo1 = Geometry(0,1)
print geo1

Upvotes: 0

Views: 135

Answers (3)

MSeifert
MSeifert

Reputation: 152607

Just to present an alternative using __new__ and the fact that instance variables and class variables are not the same:

class Geometry(object):
    # create a class variable
    id = 0
    def __new__(cls, *args, **kwargs):
        # Create a new object
        obj = object.__new__(cls, *args, **kwargs)
        # assign the next id as instance variable
        obj.id = cls.id
        # increment the class variable
        cls.id += 1
        # return the object
        return obj

    def __init__(self):
        pass

>>> geo1 = Geometry()
>>> print(geo1.id)
0
>>> geo2 = Geometry()
>>> print(geo2.id)
1
>>> geo3 = Geometry()
>>> print(geo3.id)
2

Upvotes: 0

hiro protagonist
hiro protagonist

Reputation: 46849

Geometry could have its own 'static' instance counter:

class Geometry (object):

    current_id = 0

    def __init__(self):

        self.id = Geometry.current_id
        Geometry.current_id += 1


geo0 = Geometry()
print(geo0.id)  # -> 0
geo1 = Geometry()
print(geo1.id)  # -> 1

every time you call __init__ the counter gets increased by one.

as far as i know the built-in id function can not be overridden.

Upvotes: 1

sarnthil
sarnthil

Reputation: 405

Keep the next id in a class attribute:

class Geometry(object):
    next_id = 0
    def __init__(self):
        self.id = Geometry.next_id
        Geometry.next_id += 1

The counter Geometry.next_id is saved in the class, not the instance, so it will be incremented on each instance generation:

>>> geo1 = Geometry()
>>> geo1.id
0
>>> geo2 = Geometry()
>>> geo2.id
1

Upvotes: 1

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