Python Program to Swap Two Numbers

You can swap two numbers in Python using a, b = b, a which exchanges their values in one line.

Examples

Inputa = 5, b = 10

OutputAfter swapping: a = 10, b = 5

Inputa = -3, b = 7

OutputAfter swapping: a = 7, b = -3

Inputa = 0, b = 0

OutputAfter swapping: a = 0, b = 0

How to Think About It

To swap two numbers, think of exchanging their values so that the first number gets the second number's value and vice versa. You can do this by temporarily holding one value or using Python's ability to swap directly without extra storage.

Algorithm

1

Get the two numbers as input.

2

Use Python's tuple unpacking to assign the first number to the second variable and the second number to the first variable.

3

Print or return the swapped values.

Code

python

a = 5
b = 10
print(f"Before swapping: a = {a}, b = {b}")
a, b = b, a
print(f"After swapping: a = {a}, b = {b}")

Output

Before swapping: a = 5, b = 10
After swapping: a = 10, b = 5

Dry Run

Let's trace swapping a=5 and b=10 through the code

1

Initial values

a = 5, b = 10

2

Swap operation

a, b = b, a means a gets 10, b gets 5

3

Final values

a = 10, b = 5

Step	a	b
Initial	5	10
After swap	10	5

Why This Works

Step 1: Tuple unpacking

Python allows assigning multiple variables at once using a, b = b, a, which swaps values without needing a temporary variable.

Step 2: No temporary storage needed

This method avoids extra memory use by directly swapping values in one statement.

Step 3: Simple and readable

The code is easy to read and understand, making it ideal for beginners.

Alternative Approaches

Using a temporary variable

python

a = 5
b = 10
temp = a
a = b
b = temp
print(f"After swapping: a = {a}, b = {b}")

This is the classic way but uses extra memory for the temporary variable.

Using arithmetic operations

python

a = 5
b = 10
a = a + b
b = a - b
a = a - b
print(f"After swapping: a = {a}, b = {b}")

Swaps without extra memory but can cause overflow with very large numbers.

Using XOR bitwise operator

python

a = 5
b = 10
a = a ^ b
b = a ^ b
a = a ^ b
print(f"After swapping: a = {a}, b = {b}")

Swaps without extra memory and no overflow risk but less readable.

Complexity: O(1) time, O(1) space

Time Complexity

Swapping two numbers is a constant time operation because it involves a fixed number of assignments.

Space Complexity

The tuple unpacking method uses constant space, no extra memory beyond the variables themselves.

Which Approach is Fastest?

All methods run in constant time, but tuple unpacking is fastest and most readable, while arithmetic and XOR methods are clever but less clear.

Approach	Time	Space	Best For
Tuple unpacking	O(1)	O(1)	Readability and simplicity
Temporary variable	O(1)	O(1)	Classic method, easy to understand
Arithmetic operations	O(1)	O(1)	No extra memory but risk overflow
XOR bitwise operator	O(1)	O(1)	No extra memory, no overflow, less readable