Python id() function explanation with examples

Learn how Python id() function works with examples:

The id function is used to get the identity of an object. It returns one integer value which is a unique value and constant value for that object. We may get unique ids if two objects have a non-overlapping lifetime.

Syntax of id() function:

The syntax of id() function is:

id(object)

We need to pass the object and it returns the identity of the object, which is an integer value.

Other than objects, we can also pass a string, list, tuple, integer etc. to this function.

Example of id() function with numbers:

The below program shows how the id() function works with numbers:

x = 10
y = 20
z = 10
x1 = x

print('id of x: ',id(x))
print('id of y: ',id(y))
print('id of z: ',id(z))
print('id of x1: ',id(x1))

It will print:

id of x:  2347957709392
id of y:  2347957709712
id of z:  2347957709392
id of x1:  2347957709392

As you can see here, the id() function returns different numbers as the ids. The ids of x, z and x1 are the same because these variables are equal i.e. 10.

Example of id() function with strings:

The below program shows how the id() function works with different strings:

str1 = 'hello'
str2 = 'world'
str3 = 'hello'
str4 = str2

print('id of str1: ',id(str1))
print('id of str2: ',id(str2))
print('id of str3: ',id(str3))
print('id of str4: ',id(str4))

It will print:

id of str1:  3068235986800
id of str2:  3068235897968
id of str3:  3068235986800
id of str4:  3068235897968

The ids of str1 and str3 are equal because the strings are the same.
The ids of str2 and str4 are equal because both are referring to the same string.

Example of id() function with list:

Let’s use it with lists:

list1 = ['hello', 'world']
list2 = ['hello', 'world']
list3 = ['hello']

print('id of list1: ',id(list1))
print('id of list2: ',id(list2))
print('id of list3: ',id(list3))

Even though the contents of list1 and list2 are the same, it will produce different ids for both.

id of list1:  2280471356352
id of list2:  2280471644992
id of list3:  2280471706816

Example of id() function with custom objects:

We can use the id() function with custom objects. It will produce different ids even if the content of the objects is similar.

class Student:
    name = 'Alex'

std1 = Student()
std2 = Student()
std3 = std1

print('id of std1: ',id(std1))
print('id of std2: ',id(std2))
print('id of std3: ',id(std3))

In this example, the Student class has only one property name, which is equal to ‘Alex’.

If you run this program, it will print:

id of std1:  1538234523264
id of std2:  1538234523216
id of std3:  1538234523264

The ids of std1 and std2 are different. Since both std3 and std1 are referring to the same objects, the ids are the same for these two.

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