Python round() Function

The round() function in Python is used to round a number to the nearest integer or to a specified number of decimal places. It’s simple, effective, and very commonly used in mathematical and financial calculations.

Syntax

round(number, ndigits)

Parameters:

• number – The number to be rounded (int or float).
• ndigits (optional) – The number of decimal places to round to. If omitted, it rounds to the nearest integer.

Returns:

• The rounded number (int if ndigits is not given; float if ndigits is provided).

Example 1: Round to Nearest Integer

print(round(5.7))

6

Example 2: Round Down

print(round(5.4))

5

Example 3: Round to Decimal Places

print(round(3.14159, 2))

3.14

Use Case: Financial Rounding

amount = 123.4567
rounded_amount = round(amount, 2)
print("Final bill amount:", rounded_amount)

Final bill amount: 123.46

Rounding Even Numbers (Bankers’ Rounding)

Python uses “round half to even” also known as “bankers’ rounding.”

print(round(2.5))  # Rounds to even number
print(round(3.5))  # Also rounds to even number

2
4

Common Mistakes

• Passing a string instead of a number → raises TypeError
• Expecting math.ceil or floor behavior – use math.ceil() or math.floor() for those cases
• Assuming round always rounds up – it depends on the value and follows "round half to even"

Interview Tip

The round() function is commonly used in data formatting and financial calculations. Be ready to explain how rounding works, especially the even-number rounding logic.

Summary

• round(x) → rounds to nearest integer
• round(x, n) → rounds to n decimal places
• Follows “round half to even” strategy (not always up)

Practice Problem

Ask the user to enter a number and the number of decimal places. Print the rounded result.

num = float(input("Enter a number: "))
decimals = int(input("Round to how many decimal places? "))
print("Rounded result:", round(num, decimals))