Rotate List Right by k
Implement a function that rotates a list to the right by k positions.
Running Total Window
Implement a function that returns a list of running totals, resetting to zero after each positive sum.
Normalize Array to Zero-One Range
Implement a function that normalizes a list of numbers to the range [0,1] using min-max scaling.
Boolean Mask Filter
Write a function that filters a list using a boolean mask and returns the matching elements as a list.
Flatten Multidimensional Lists
Write a function that flattens arbitrarily nested lists of integers into a single list.
Concatenate Horizontally
Write a function that horizontally concatenates two 2D lists into a new 2D list.
Pad array edges
Implement a function that pads a list on both ends with a given value to a specified total length.
Merge dicts summing values
Write a function that merges two dictionaries by summing values for duplicated keys.
Are two lists the same multiset
Write a function that checks if two lists contain the same elements with the same multiplicities, ignoring order.
Word to Index Map
Create a function that returns a dictionary mapping each unique word to the index of its first occurrence.
Missing keys default zero
Write a function to sum numeric values from dictionaries, treating missing keys as zero.
Nested get with dotted path
Implement a function that safely retrieves a value from a deeply nested dictionary using a dot-separated path, returning a default if any key is missing.
Common Keys of Two Dictionaries
Implement a function that finds keys shared by two dictionaries and returns them sorted.
Union of Many Sets
Implement a function that takes any number of sets and returns a sorted list of their union.
Mode of a list via counting
Implement a function that returns the mode of a list, resolving ties by the element that appears first.
Replace keys with a mapping
Write a function that renames keys in a dictionary according to a mapping, with duplicate handling.
Symmetric Difference
Write a function that computes the symmetric difference of two lists, returning a sorted list of unique elements.
Subset of another set
Write a function that checks if every element of one set is contained in another.
Frequency sort descending
Write a function that sorts a list by frequency descending while preserving original order for ties.
Count Pairs with Sum
Implement a function that counts the number of distinct pairs in a list summing to a target.
Group by Department
Implement a function that groups a list of employee dictionaries by department, returning a dictionary keyed by department with lists of employee dictionaries.
Revenue by Month
Write a function that groups a list of (date, amount) pairs by year-month and returns total revenue per month as a sorted dictionary.
Pivot sales by product
Write a function that pivots sales records into a dictionary keyed by product with monthly totals.
Bind First Argument
Implement bind_first_arg, a decorator that fixes the first argument of any function.
Showing 145–168 of 286 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.