Recursive Functions Part 1

Part of the Logic & Flow section of Coddy's Python journey — lesson 60 of 78.

A recursive function is a function that calls itself to solve smaller instances of a problem. Each recursive call must bring the function closer to a base case, which stops the recursion.

Example: Summing numbers from 1 to n:

def sum_to_n(n):
    if n == 0:  # Base case
        return 0
    return n + sum_to_n(n - 1)  # Recursive step

print(sum_to_n(5))  # Output: 15

Challenge

Easy

Write a recursive function named count_down that takes a positive integer n as an argument and prints each number from n down to 0.

Cheat sheet

A recursive function calls itself to solve smaller instances of a problem. Each recursive call must bring the function closer to a base case, which stops the recursion.

Basic structure:

def recursive_function(parameter):
    if base_case_condition:  # Base case
        return base_value
    return recursive_step  # Recursive step

Example - summing numbers from 1 to n:

def sum_to_n(n):
    if n == 0:  # Base case
        return 0
    return n + sum_to_n(n - 1)  # Recursive step

print(sum_to_n(5))  # Output: 15

Try it yourself

def count_down(n):
    # Write code here

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Logic & Flow

1Variables Exploration

Constants Multiple Variable Assignments Swapping Variables Placeholder Variables Round Numbers List Casting

4Contact Book Application

Display Menu Add Contact

7Sets Part 2

Mathematical Operations Part 1 Mathematical Operations Part 2 Recap - Treasure Hunt Subsets and Supersets Iterating Over Sets Recap - Tournament Tracker

10Basic List Comprehensions

The Syntax Creating Simple Lists Adding Conditions Using Data Aggregation Recap - House Of Lists Recap - Elements Of Freedom

13Inventory Management System

Project Overview Add Item

Update Stock

Check Availability

Generate Report

2Dictionaries Part 1

What is a Dictionary?Creating a Dictionary Accessing Values Modifying Dictionaries Recap - Recipe Manager

5Advanced Decision Making

Ternary Operator Membership Checks Identity Checks Indentation Errors Recap - Vacation Filter

8Student Records Manager

Project Overview Add Student

11Advanced Functions

Returning Multiple Values Lambda Functions Part 1 Lambda Functions Part 2 Recap Challenge - Lambda SortRecursive Functions Part 1Recursive Functions Part 2 Recap - Sum Nested List

14Higher-Order Functions

The Map Function The Filter Function Recap - Email Validator Recap - Number Processor

3Dictionaries Part 2

Dictionary Methods Nested Dictionaries Checking for Keys Looping Through Dictionaries Recap - Frequency Counter

6Sets Part 1

What is a Set?Basic Operations Set Methods Recap - Remove Duplicates

9Advanced Data Aggregation

Using Sum Finding Minimum and Maximum Sorting Data Efficiently Recap - Dictionary Sorter

12Basic Error Handling

What is Error Handling?The Try and Except Block Handling Multiple Exceptions Recap - Shopping Cart Errors

15Final Challenges

Smart Contact Manager Word Analytics Data Transformer