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Python id() Function

The id() method returns a unique integer (identity) of a passed argument object.

note

Since ID is an assigned memory address, it can be different in different systems. So, the output on your system can be different.

Syntax​

id(object)

id() Parameters​

Python id() function parameters:

ParameterConditionDescription
objectRequiredAny Python object whose identity is required. It can be a class, variable, list, tuple, set, etc.

id() Return Value​

Python id() function returns the identity of the object (which is a unique integer for a given object)

Examples​

Example 1: Basic Examples​

# id of 5
print("id of 5 =", id(5))

a = 5
# id of a
print("id of a =", id(a))

b = a
# id of b
print("id of b =", id(b))

c = 5.0
# id of c
print("id of c =", id(c))

output

id of 5 = 136596395200712
id of a = 136596395200712
id of b = 136596395200712
id of c = 136596384063184

Notice that we have used the id() function with variables a, b and c and got their corresponding ids: the id() function returns the integer 136596395200712 for both a = 5 and 5. This because both values are the same, and so the id is also the same.

Example 2: id() function with Classes and Objects​

class Food:
    banana = 15

my_food = Food()

#  id of the object my_food
print(id(my_food))

output

132413969081424

Example 3: id() function with Sets (Mutable Objects)​

d1 = {"A":  1, "B":  2}
d2 = {"A":  1, "B":  2}

print(id(d1))  # Output: Different from id(d2) because dictionaries are mutable
print(id(d2))

output

134716606985664
134716607036672

Example 4: id() function with Tuples (Immutable Objects)​

t1 = (1,  2,  3)
t2 = (1,  2,  3)

print(id(t1))  # Output: Same as id(t2) because they are the same object
print(id(t2))

output

139212483455616
139212483455616

Example 5: id() with Sets​

colors = {"red", "yellow", "blue", "green"}

# id() of the set colors
print("The id of the colors set is", id(colors))

output

The id of the colors set is 133643641542400

Example 6: Different Identities for Different Instances​

class MyClass:
    pass

obj1 = MyClass()
obj2 = MyClass()

print(id(obj1))  # Output: Unique id for obj1
print(id(obj2))  # Output: Unique id for obj2

output

139946208764944
139946208765008

Example 7: Compare Two IDs using is keyword​

To check if two objects have same id, use is keyword.

For example, check if 'x' and 'y' have the same id (i.e. if they point to the same object)

x = 42
y = x
print(x is y)   # Output: True

output

True
note

is keyword is used for identity (id) comparison, while == operator is used for equality (value) comparison.

Particular exceptions with id in Python​

In Python, every object has its own unique id. However, for the sake of optimization, there are some exceptions.

Some objects have same id (actually one object with multiple pointer), like:

  • Small integers between -5 and 256
    • Python optimizes memory usage by caching a range of small integers, from -5 to 256. When you use these numbers, Python will always refer to the same memory address. For example, id(-5) and id(256) will give you the same ID because they are both cached
  • Small interned strings (usually less than 20 character)
    • Python creates a pool of immutable objects called "interned strings". When you create a string that is already in this pool, Python will return a reference to the existing object rather than creating a new one. This applies to strings of length 0 to 20 characters. So, if you create a string with the same content as an existing interned string, it will have the same ID.
print(30 is 20+10)      # Output: True
print('aa'*2 is 'a'*4)  # Output: True

output

True
True

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