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Python Program to Swap Two Variables

Beginner · Basics

Swapping two variables means exchanging their values: if a is 5 and b is 10, afterwards a is 10 and b is 5. This program uses a temporary third variable, the method taught in most textbooks, and the alternatives show the shorter Python way.

Program

swap_two_variables.py
a = 5 # or: a = int(input("Enter a: "))
b = 10 # or: b = int(input("Enter b: "))
print(f"Before swapping: a = {a}, b = {b}")
# Use a third variable to hold one value for a moment
temp = a
a = b
b = temp
print(f"After swapping: a = {a}, b = {b}")
Output
Before swapping: a = 5, b = 10
After swapping: a = 10, b = 5

How it works

  1. temp = a keeps a copy of the first value, because the next line overwrites a.
  2. a = b copies the second value into a.
  3. b = temp puts the saved first value into b, completing the swap.
  4. Without temp, writing a = b and then b = a would leave both variables holding 10.

Other ways to write it

Using tuple unpacking

Using tuple unpacking
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

Python works out the right side b, a first, then assigns both values at once. This is the usual way to swap in Python.

Using addition and subtraction

Using addition and subtraction
a = 5
b = 10
a = a + b # a is now 15
b = a - b # b is now 5
a = a - b # a is now 10
print(f"After swapping: a = {a}, b = {b}")
Output
After swapping: a = 10, b = 5

This trick avoids a third variable but only works for numbers, so it mostly appears in exams and interviews.

Try it yourself

Add a third variable c and rotate the values so a gets the value of b, b gets c and c gets a.

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