Python 3 reference · Built-in Functions

Python id() Function

Return an object's identity: a unique integer for the object while it exists. In CPython it is the memory address.

Syntax

id(object)

Parameters

Parameter	Description
`object`	Any object.

Return value

An int, unique among objects alive at the same time.

Examples

Same object or just equal?Try it yourself

a = [1, 2]
b = a          # the same list
c = [1, 2]     # an equal but different list
print(id(a) == id(b), id(a) == id(c))
print(a is b, a is c, a == c)

Output

True False
True False True

Functions receive the same objectTry it yourself

def add_item(items):
    items.append("new")
    return id(items)

shopping = []
print(add_item(shopping) == id(shopping), shopping)

Output

True ['new']

Good to know

Use is to compare identity rather than comparing id() values. Two objects with non-overlapping lifetimes may get the same id().

Version history

Version	Change
Python 3.0	Added

hash() · Return the hash value of an object: an integer used by dicts and sets to find keys quickly. Only immutable values are hashable.
type() · With one argument, return an object's type. With three arguments, create a new class dynamically.
Python Variables · tutorial