Practice Arena

Python Coding
Challenges

Write real Python in the browser. Instant feedback. From beginner to expert.

925 challenges 556 easy 323 medium 46 hard

All Easy Medium Hard

All Python Basics Strings & Text Lists & Arrays Dicts & Sets Functions & Closures OOP & Classes Data Structures & Algorithms Advanced Python Iterators & Generators Decorators & Context Managers Error Handling & Exceptions Regular Expressions Math & Number Theory Bit Manipulation Dynamic Programming Trees & Binary Trees Graphs & Graph Algorithms Recursion & Backtracking Greedy Algorithms Binary Search Two Pointers & Sliding Window Stacks & Queues Heaps & Priority Queues Linked Lists Matrix & 2D Arrays Datetime & Time Calculations Data Formats & Parsing SQL & SQLite Numpy & Vectorized Computing Cryptography & Hashing

Dicts & Sets easy

Top K Frequent Words

Given a list of words, return the k most frequent words sorted by frequency (descending) and then alphabetically.

dictionary sorting frequency

Dicts & Sets easy

Ransom Note Builder

Given two strings, determine if the ransom note can be formed from the words in the magazine.

dictionary counting strings

Dicts & Sets easy

Pivot sales by product

Write a function that pivots sales records into a dictionary keyed by product with monthly totals.

dicts grouping aggregation

Data Structures & Algorithms easy

Valid parentheses

Return True if brackets in the string close in the correct order.

Error Handling & Exceptions easy

Parse Error Recovery

Parse a whitespace-separated string into a list of valid integers, skipping invalid tokens.

parsing exceptions error-handling

Regular Expressions easy

Validate Hex Color Code

Write a function that validates hex color codes using regular expressions.

regex validation strings

Regular Expressions easy

Multiline anchor match

Extract lines beginning with a plain-text prefix from multiline strings using Python's re module.

regex anchors multiline

Regular Expressions easy

Match Balanced Parentheses with Regex

Write a function that uses regular expressions to determine if parentheses are balanced and properly nested.

regex strings validation

Bit Manipulation easy

Compress Bits Run

Write a function that compresses a binary string by representing consecutive identical bits as a count-bit pair.

bit-manipulation strings compression

Two Pointers & Sliding Window easy

Longest Substring Without Repeating Characters

Implement a function that returns the length of the longest substring without repeating characters.

strings sliding-window two-pointers

Datetime & Time Calculations easy

Format date output

Parse ISO date strings and format them into a friendly US-style date output.

datetime string-formatting date-parsing

Datetime & Time Calculations easy

Duration Human Readable

Write a function that turns a number of seconds into a human-readable duration like '2 hours, 1 minute'.

datetime strings formatting

Data Formats & Parsing easy

Protocol definition

Parse a simple wire protocol string into a structured dictionary.

parsing protocol strings

Data Formats & Parsing easy

Config Parser Reader

Parse a simple INI-style configuration text into a nested dictionary.

parsing strings config

Data Formats & Parsing easy

Generate CSV row

Implement a function that converts a list of values into a single CSV row with correct quoting and escaping.

csv escaping strings

Data Formats & Parsing easy

Parse email header

Write a function that parses a raw email header string and returns sender, recipient, and subject.

parsing strings email

Data Formats & Parsing easy

Encode Base64 String

Write a function that encodes a UTF-8 string into a base64 string without using the base64 module.

base64 encoding strings

Data Formats & Parsing easy

Parse CSV Row

Implement a robust function that parses a single CSV line into a list of fields, handling double quotes and escaped quotes.

csv parsing strings

Data Formats & Parsing easy

Parse Apache log line

Write a function that parses a single Apache access log line into a dictionary with IP, timestamp, request, status, and size.

parsing strings regex

Data Formats & Parsing easy

Parse table rows

Implement a function that converts a simple text table into a list of dictionaries.

parsing strings csv

Cryptography & Hashing easy

Constant Time Compare

Write a function that compares two strings without leaking length or content via timing.

constant-time security comparison

Cryptography & Hashing easy

XOR Cipher Encode

Implement the XOR cipher: encode a string by XORing each character with a key character.

xor encryption strings

Cryptography & Hashing easy

Constant time compare

Write a function that compares two strings in constant time to avoid timing attacks.

timing-safe security strings

Showing 97–119 of 119 challenges · easy

Guide: free Python coding challenges

Practice Python by solving problems

PythonSkillset challenges are hands-on coding exercises from beginner to advanced. Open a challenge, read the problem, write Python in the split-pane editor, and run tests with Pyodide — no install required.

How to use the arena

Pick a category — basics, algorithms, strings, and more
Open a challenge, read the statement, and edit the starter code
Run tests, fix failures, then try a related quiz or tutorial lesson

Challenges vs tutorials and quizzes

Challenges test what you can build under constraints. For guided teaching, use our Python tutorials. For quick checks, try quizzes or copy snippets from code samples.