README.md

Python Self-Learning: From Zero to Interview-Ready

A browser-based Python learning site. Work through beginner problems, follow interactive tutorials, and practice data-structure interview questions — all with instant feedback and no installation required.

Who is this for?

Section	Problems	Who it's for
Tutorial	52 exercises	Complete beginners — never written a line of code
Beginner	40 problems	Just starting out — learning syntax and basic concepts
Intermediate	30 problems	Getting comfortable — loops, functions, and algorithms
Advanced	8 problems	Solid foundation — OOP, comprehensions, error handling
Interview Prep	53 problems	Job seekers — LeetCode-style data structure problems

Features

• Three learning tracks — classic problems (Beginner/Intermediate/Advanced), guided tutorials, and Interview Prep
• In-browser Python — powered by Pyodide (WebAssembly); no server, no setup
• Common stdlib pre-imported — Counter, defaultdict, deque, heapq, and math are always available so students focus on problem-solving, not imports
• Line-numbered code editor — with Tab-to-indent and auto-indent on Enter
• Progress tracking — solved problems saved in localStorage; last submitted code per interview problem is also restored on revisit
• Zero dependencies — pure HTML, CSS, and JavaScript; works offline after first load

Learning Tracks

Classic Problems (78 total)

Output-based grading: your code's stdout is compared against the expected output. For concept-specific problems the grader also checks that required keywords appear in your code (e.g. def, len(, class).

Level	Count	Topics
Beginner	40	Printing, variables, strings, lists, arithmetic, type conversion
Intermediate	30	Loops, functions, conditionals, sorting, recursion
Advanced	8	Dictionaries, classes, list comprehensions, error handling

Tutorial (13 topics, 52 exercises)

Each topic has a Learn panel (what it is, when to use it, a worked example) followed by short free-form practice exercises graded by output.

Topics: Your First Line of Code · Numbers and Math · Variables · Booleans · Strings · Lists · Dictionaries · Functions · Loops · Conditionals · Classes · Comprehensions · Error Handling

Interview Prep — Classic Data Structures (9 topics, 53 problems)

Function-based grading: your code is called with test inputs and the return value is compared. Each problem links to its LeetCode page and shows 2–3 labeled examples. After running, shows (x/y) tests passed and, on failure, the first failing input with labeled parameter names. Each problem has 8–10 test cases covering edge cases.

Topic	Problem	LC#	Difficulty	Pattern
Array	Two Sum	1	Easy	Hash map for complement lookup
	Best Time to Buy and Sell Stock	121	Easy	Running minimum + max profit
	Contains Duplicate	217	Easy	Hash set membership
	Maximum Subarray	53	Easy	Kadane's algorithm
	Product of Array Except Self	238	Medium	Prefix / suffix products
Hash Map	Valid Anagram	242	Easy	Character frequency count
	Ransom Note	383	Easy	Frequency subset check
	Word Pattern	290	Easy	Bijection mapping
	First Unique Character	387	Easy	Ordered frequency count
	Longest Consecutive Sequence	128	Medium	Hash set + sequence-start detection
Stack	Valid Parentheses	20	Easy	Matching brackets with stack
	Baseball Game	682	Easy	Stack simulation
	Remove Outermost Parentheses	1021	Easy	Depth tracking with stack
	Backspace String Compare	844	Easy	Stack to process deletions
	Daily Temperatures	739	Medium	Monotonic stack
Queue & Deque	Number of Students Unable to Eat Lunch	1700	Easy	Queue simulation
	Implement Queue using Stacks	232	Easy	Two-stack queue design
	Implement Stack using Queues	225	Easy	Queue-based stack design
	Number of Recent Calls	933	Easy	Sliding window with deque
	Design Circular Queue	622	Medium	Circular buffer design
Heap	Last Stone Weight	1046	Easy	Max-heap simulation (negate)
	Kth Largest Element in a Stream	703	Easy	Min-heap of size k
	K Weakest Rows in a Matrix	1337	Easy	Heap with tuple keys
	Top K Frequent Elements	347	Medium	Heap + frequency count
	Kth Largest Element in an Array	215	Medium	Min-heap of size k / quickselect
Linked List	Reverse Linked List	206	Easy	In-place pointer reversal
	Merge Two Sorted Lists	21	Easy	Merge with dummy head
	Remove Linked List Elements	203	Easy	Dummy head traversal
	Middle of the Linked List	876	Easy	Slow / fast pointer
	Remove Nth Node From End	19	Medium	Two-pointer gap of n
Binary Tree	Maximum Depth of Binary Tree	104	Easy	DFS recursion
	Invert Binary Tree	226	Easy	Recursive left/right swap
	Symmetric Tree	101	Easy	Mirror comparison DFS
	Path Sum	112	Easy	DFS with running sum
	Lowest Common Ancestor of BST	235	Easy	BST property navigation
	Binary Tree Level Order Traversal	102	Medium	BFS level-by-level
	Validate Binary Search Tree	98	Medium	DFS with min/max bounds
Graph	Flood Fill	733	Easy	Grid DFS
	Max Area of Island	695	Easy	Grid DFS + area counting
	Number of Provinces	547	Medium	Connected components DFS
	Number of Islands	200	Medium	Classic grid graph DFS/BFS
	Rotting Oranges	994	Medium	Multi-source BFS
	Course Schedule	207	Medium	Cycle detection (topological sort)
	Course Schedule II	210	Medium	Topological sort ordering
Sorting & Binary Search	Binary Search	704	Easy	Classic lo/hi template
	Search Insert Position	35	Easy	Lower-bound binary search
	First Bad Version	278	Easy	Binary search on answer
	Sort Colors	75	Easy	Dutch National Flag (3-way partition)
	Find Minimum in Rotated Sorted Array	153	Medium	Rotated array binary search
	Search in Rotated Sorted Array	33	Medium	Rotated array + target
	Find First and Last Position of Element	34	Medium	Left / right boundary search
	Merge Intervals	56	Medium	Sort by start + sweep to merge
	Search a 2D Matrix	74	Medium	Flatten 2D to 1D binary search

Running Locally

No build step needed. Use the included server script:

python3 server.py 8080

Then open http://localhost:8080.

The script sets the Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy headers required by Pyodide. Plain python3 -m http.server will not work because those headers are missing.

How It Works

• Python runs entirely in the browser via Pyodide (WebAssembly)
• On load, common stdlib names are pre-imported into the Pyodide global namespace so they are always available regardless of problem order
• Classic / Tutorial grading: stdout is captured into a StringIO buffer and compared against expectedOutput
• Interview grading: user code is executed to define the function, then a test runner calls it with each test case's args and compares the return value to expected; linked-list and tree arguments are automatically converted to/from ListNode/TreeNode objects
• Progress is stored in localStorage under the key pylearn_solved; last-submitted interview code is stored under pylearn_interview_code

Project Structure

index.html   — app shell; five views (level select, problems, editor, tutorial, interview)
app.js       — view routing, Pyodide loading, code execution, grading, editor behaviour
data.js      — all content: PROBLEMS (classic), TUTORIAL, INTERVIEW
style.css    — styles
server.py    — minimal static file server with required COOP/COEP headers

License

MIT