How to Use Fractions Module in Python: Simple Guide

Use the fractions module in Python by importing it and creating Fraction objects to represent rational numbers exactly. You can create fractions from integers, floats, or strings and perform arithmetic with them.

Syntax

The fractions module provides the Fraction class to create rational numbers. You import it with from fractions import Fraction. Then, create a fraction using Fraction(numerator, denominator) or from a string like Fraction('3/4').

Key parts:

• Fraction: class to represent fractions
• numerator: integer numerator
• denominator: integer denominator (not zero)
• Can also create from strings or floats

python

from fractions import Fraction

# Create fraction from numerator and denominator
f1 = Fraction(3, 4)

# Create fraction from string
f2 = Fraction('5/6')

# Create fraction from float
f3 = Fraction(0.5)

Example

This example shows how to create fractions, add them, and print the result as a fraction and a float.

python

from fractions import Fraction

f1 = Fraction(1, 3)
f2 = Fraction('2/5')

result = f1 + f2

print('Sum as fraction:', result)
print('Sum as float:', float(result))

Output

Sum as fraction: 11/15
Sum as float: 0.7333333333333333

Common Pitfalls

Common mistakes include:

• Using floats directly can cause precision issues because floats are approximate.
• Passing a float to Fraction without converting can give unexpected results.
• Denominator cannot be zero.

Always prefer creating fractions from strings or integers for exact values.

python

from fractions import Fraction

# Wrong: float approximation problem
f_wrong = Fraction(0.1)
print('From float 0.1:', f_wrong)

# Right: create from string for exact fraction
f_right = Fraction('0.1')
print('From string "0.1":', f_right)

Output

From float 0.1: 3602879701896397/36028797018963968
From string "0.1": 1/10

Quick Reference

Summary tips for using fractions module:

• Import with from fractions import Fraction
• Create fractions from integers, strings, or floats (prefer strings for exactness)
• Use arithmetic operators (+, -, *, /) directly on Fraction objects
• Convert to float with float() if needed
• Denominator must not be zero

Key Takeaways

Import the fractions module and use Fraction to represent exact rational numbers.

Create fractions from strings or integers to avoid float precision errors.

You can do math directly with Fraction objects using normal operators.

Avoid creating fractions directly from floats unless you understand precision limits.

Convert fractions to float when you need approximate decimal values.