Python id(): Get the Memory Address of an Object

The id() function returns the unique memory address of an object. It’s useful for checking object identity, debugging, and understanding how Python handles variables in memory.

Example

x = 42
print(id(x))  
# Output: (Unique memory address)

Each variable has a unique identifier based on its memory location.

Syntax

id(object)

object → The variable or object to check.
Returns → A unique integer representing the memory address.

1. Checking If Two Variables Point to the Same Object

a = 100
b = a

print(id(a) == id(b))  
# Output: True

Since b references the same object as a, both have the same id.

2. Comparing Mutable and Immutable Objects

Mutable objects change memory location when modified.

list1 = [1, 2, 3]
list2 = list1  # Same reference

print(id(list1) == id(list2))  # Output: True

list1.append(4)  # Modify list1
print(id(list1) == id(list2))  # Output: True (Same memory location)

Since lists are mutable, changes affect both list1 and list2.

Immutable objects get a new memory location when modified

x = 10
y = x  # Same reference

print(id(x) == id(y))  # Output: True

x += 1  # Creates a new object
print(id(x) == id(y))  # Output: False

Numbers, strings, and tuples are immutable, so modifying them creates new objects.

3. Checking Object Identity in Functions

Use id() to see if a function modifies an object in-place.

def modify(lst):
    print("Before:", id(lst))
    lst.append(100)
    print("After:", id(lst))

nums = [1, 2, 3]
modify(nums)

# Output:
# Before: (Memory address)
# After: (Same memory address)

This proves that lists are modified in-place.

Key Notes

✔ Returns a unique identifier (memory address) for an object.
✔ Shows if two variables point to the same object.
✔ Immutable objects get new memory addresses when modified.
✔ Useful for debugging and understanding variable behavior.

By using id(), you can check how Python manages memory, making it easier to debug and optimize your code. 🚀