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Object Value vs Object Identity

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In Python, every object that is created is given a number that uniquely identifies it. It is guaranteed that no two objects will have the same identifier during any period in which their lifetimes overlap. Once an object’s reference count drops to zero and it is garbage collected, then its identifying number becomes available and may be used again.

The built-in Python function id() returns an object’s integer identifier. Using the id() function, you can verify that two variables indeed point to the same object.

reblark on Dec. 10, 2019

Everything in Python is an object—is a variable an object? I know that it points to an assigned value which is an object, but is it an object?

Martin Breuss RP Team on Dec. 10, 2019

Hehe, philosophical! No, a variable is a reference to an object, not an object itself. Like the shadows on Plato’s cave wall 😜…

reblark on Dec. 11, 2019

I suspected as much, but your statement is “everything in Python is an object.” A variable is a thing. Picky, picky, picky. BTW, I didn’t know there were shadows on Plato’s cave wall. Are you sure? Maybe at the entrance. :-)

Martin Breuss RP Team on Dec. 14, 2019

Almost. A variable is a reference to a thing. A variable itself doesn’t have a memory location (it’s not “a thing”) but only points to a thing (=an object).

Maybe we could agree on “Everything in Python that has a memory location is an object”–but I think that does sound less catchy!

There are shadows in Plato’s cave–but I don’t think the allegory to variables and objects holds that well apart from that.

John T on Jan. 13, 2020

Hi I’m a bit confused with the example . My understanding has always been that all variables that reference the same value will have the same id. i.e if n =300 and m=300 then id(n) == id(m) will be True.

John T on Jan. 13, 2020

pls ignore my last comment guys

kingjay2498 on March 12, 2020

I am bit confused, Need help! if two object ids are different in memory , but has the same Object VALUE shouldnt objects ids be different right?

For example : n = 300 m = 300 # object ids are different , yet the object value is the same print(id(n)) print(id(m))

In your videos when you ran code the object ids were different ,

but when I use your example an ran code the object ids were the exact same , why is that? I dont get it my example: n = 300 m = 300 print(id(n)) print(id(m))

also when I compare both object ids the answer came back TRUE instead of false ? Confused ? Can anybody help me!:/

kingjay2498 on March 12, 2020

In referring to my last comment objects ids keep popping up the same 1887265792816 1887265792816

Martin Breuss RP Team on March 12, 2020

It might be related to your Python version @kingjay2498. Make sure to check the excellent comments in the upcoming video section. Hope that helps to shed some light on your particular situation.

Ajay on May 24, 2020

Hi Team, I was trying same example in my interpreter and got below different outputs:


In [1]: n = 300

In [2]: m = 400

In [3]: id(n)
Out[3]: 83420736

In [4]: id(m)
Out[4]: 83420912

In [5]: n = 300

In [6]: m = 300

In [7]: id(n)
Out[7]: 83420928

In [8]: id(m)
Out[8]: 83420768

User editor thonny

n = 300
m = 400
# id tells where object lives in memory
print (f"id of n {id(n)}")
print (f"id of m {id(m)}")
n = 300
m = 300
# id tells where object lives in memory
print (f"id of n {id(n)}")
print (f"id of m {id(m)}")

Output id of n 69962880 id of m 69963760 id of n 69962880 id of m 69962880

Now little confused that when i used ipython interpreter for different address for variable of same value and in editor got same value.

kiran on July 18, 2020

In [16]: a = 2

In [17]: b = 2

In [18]: id(a)
Out[18]: 8791518529216

In [19]: id(b)
Out[19]: 8791518529216

In [20]: a = 300

In [21]: b = 300

In [22]: id(a)
Out[22]: 84490864

In [23]: id(b)
Out[23]: 84489456


Martin Breuss RP Team on July 18, 2020

@manupanduworld just keep watching to the next video: realpython.com/lessons/small-integer-caching/ :)

Alain Rouleau on July 26, 2020

Martin, not to disagree with you or Plato :-) … But the names/variables are indeed objects as well. If you use the dir() function it will return a list of names/variables in the local namespace, i.e. ['n', 'm', ...]

So, you actually have a “string object” pointing to an “integer object”. And each having a memory location as well. So, in Python everything truly is an object. :-)

As for Plato, the shadows on the cave walls are objects too and not simply references. You know, class Shadow() is composed of photons which in turn simply hit Plato’s eyeballs, LOL

Joseph Flanagan on Sept. 29, 2020

Following up on Alain Rouleau, isn’t a variable a key in the globals() dictionary?

>>> my_string = 'hello'

>>> globals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <_frozen_importlib_external.SourceFileLoader object at 0x110caac88>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, '__cached__': None, 'my_string': 'hello'}

>>> globals()['my_string']

I’m not sure how this relates to the issue of names/variables as references to memory addresses, however.

Bartosz Zaczyński RP Team on Sept. 30, 2020

There are a few built-in functions in Python that let you get a dictionary of variables:

As the name implies, calling globals() will only return the global variables. (It’ll skip variables defined in a function, for example.)

Regarding variables in Python, you can think of them as labels attached to objects. They’re like yellow stickers with names written on them, but apart from that, don’t have any type, value, or identity. These are attributes of a particular object a variable is pointing to, which can change over time. That isn’t true for other languages, where variables are more like cardboard boxes with a predefined shape and size.

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