Free Handbook · Runs in your browser

Python Handbook

Learn Python by running it. Sixteen modules from your first print() to a job: every example is editable and runs right here, loops and function calls are traced line by line, and the real errors you will hit are explained with the fix. Problem-solving patterns, Python with real tools, interview questions, a certification exam, and a resume check at the end.

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How this handbook works

Every lesson has code you can edit and run right here — the interpreter runs in your browser, nothing to install, a trace of what the interpreter did line by line where that matters, and the real error you will hit next, with why the interpreter said it and the fix. Lessons tick themselves as you go. Finish the handbook, sit the exam, get the certificate, then take your resume through the ATS checker and on to jobs.

16modules

94lessons

74runnable examples

27real errors explained

Module 00 · what you'll be able to do

Run Python right here in the browser and on your own computer
Write, read and trace your first program: add two numbers
Use comments and understand what the interpreter ignores
Know how the handbook ticks lessons and how to use AI while learning without cheating yourself

Why Python

Python is the language most people learn first, and the language most working engineers still reach for daily. It reads like English, it runs almost everywhere, and it is the default in the fields that are hiring: data engineering, machine learning, automation, backend APIs, and scripting inside every cloud. That combination — easy to start, hard to outgrow — is why it is the first handbook here.

You want to…	Python gets you there with
Automate something boring	The standard library — files, dates, CSV, JSON, HTTP — with no installs
Work with data	pandas, Spark (PySpark), SQL drivers, Airflow — the whole data stack speaks Python
Build an API or a web app	FastAPI, Django, Flask
Do machine learning or AI	PyTorch, scikit-learn, every LLM SDK
Pass a coding interview	Short, readable solutions — most interviewers accept Python

What Python is not

It is not the fastest language (C, C++, Rust and Go are), and it does not run in the browser natively (JavaScript does). When speed matters, Python usually calls a library written in C — which is why pandas and NumPy are fast even though Python is not.

Running Python — in this page and on your machine

Every example in this handbook is an editor with a Run button. Press it: the first time, your browser downloads a full Python interpreter (about 12 MB, once), then every run after that is instant and entirely local — nothing you type leaves your computer. Try it now. Change the text, run it again.

pythonEdit it. ⌘/Ctrl + Enter runs.

print("Hello, world!")
print("Python is running in your browser.")

You should see

Hello, world!
Python is running in your browser.

Your turn

Change the second line to print your own name, then press Run (or ⌘/Ctrl + Enter).

On your own computer

For real projects you want Python installed locally. It takes five minutes:

1
Install it
Go to python.org/downloads and install the latest 3.x. On Windows tick "Add python.exe to PATH". On macOS and most Linux distributions it is already there — check with the next step.
2
Check it works
Open a terminal (Terminal on macOS, PowerShell on Windows) and type python3 --version (or python --version on Windows). You should see something like Python 3.13.2.
3
Run a file
Save the code above as hello.py, then run python3 hello.py. That is the whole workflow: write a file, run it.
4
Get an editor
VS Code with the Python extension is what most people use. It underlines mistakes before you run.

shell

$ python3 --version
Python 3.13.2
$ python3 hello.py
Hello, world!
Python is running in your browser.

The terminal session you should see. $ is the prompt — you do not type it.

The REPL

Type just python3 and you get a prompt (>>>) where each line runs as you press Enter. It is the fastest way to try one thing. exit() leaves it.

Your first program: add two numbers

Here is the program every Python tutorial starts with, and for good reason — it uses a variable, an operator, a function call and a formatted string, which is most of what a program is. Run it, then read the trace below to see what the interpreter actually did with each line.

pythonEdit it. ⌘/Ctrl + Enter runs.

a = 5
b = 7
total = a + b
print(f"{a} + {b} = {total}")

You should see

5 + 7 = 12

Your turn

Change a and b to decimals like 2.5 and run again. Then try a = "5" (with quotes) — read the error, and we will explain it in Module 01.

VisualizeWhat the interpreter does with those four linesStep 1 / 4

1a = 5
2b = 7
3total = a + b
4print(f"{a} + {b} = {total}")

Line 1

Create the integer 5 and bind the name a to it. A variable is a name pointing at a value — nothing is "stored in" a.

Variables now

a 5

All 4 steps as a table

Step	Line	What happened	Variables now
1	1	Create the integer `5` and bind the name `a` to it. A variable is a name pointing at a value — nothing is "stored in" `a`.	`a = 5`
2	2	Same again: the name `b` now points at `7`.	`b = 7`
3	3	Evaluate the right-hand side first: look up `a` (5), look up `b` (7), add them to get a new integer `12`. Then bind `total` to it.	`total = 12`
4	4	Build the f-string by replacing each `{…}` with the value of the expression inside it, giving `"5 + 7 = 12"`, then pass that string to `print`, which writes it followed by a newline.

Variable: A name bound to a value. a = 5 reads "let a refer to 5". Python has no declarations — the first assignment creates the name.
Expression: Anything that produces a value: 5, a + b, len("hi"). Statements (like assignment or print(...)) do something with them.
f-string: A string starting with f in which {expression} is replaced by the expression's value. The modern way to build text from values.

Quick check

After total = a + b, what happens to total if you later change a?

Comments

Anything after # on a line is a comment: the interpreter skips it entirely. Comments are for the next human — often you, next month. Write why, not what; the code already says what.

pythonEdit it. ⌘/Ctrl + Enter runs.

# Prices are in cents to avoid floating-point rounding on money.
price_cents = 1999
qty = 3

total = price_cents * qty  # still cents
print(f"${total / 100:.2f}")  # format as dollars only at the edge

You should see

$59.97

Your turn

Put a # in front of the last line and run — nothing prints. That is the quickest way to switch a line off while debugging.

Comments that waste space

x = x + 1 # add one to x
# loop over the list above a loop over the list
A block of commented-out code left for months

Comments that earn their place

# retry once: the API drops ~1% of first calls
# cents, not dollars — see invoice rounding bug #412
A one-line note on a non-obvious decision

Multi-line "comments"

Python has no block comment syntax. A string on its own line ("""like this""") is legal and ignored at runtime, which is why people use it — but the proper use of triple-quoted strings is docstrings, the first line of a function or module, which tools actually read. You meet those in Module 04.

How this handbook works

Sixteen modules, each its own page, each a set of lessons like this one. The rail on the left lists them; the bar at the top of the page and the pill at the bottom-left track how far you are. A lesson ticks itself when you reach its end or run its code, and the tick survives closing the tab — no account needed.

Run blocks are the point. Every one is meant to be edited. Break it, fix it, guess the output before you press Run.
Trace blocks (the purple ones) step through code the way the interpreter does. Use them whenever a loop or a function call feels like magic.
Error cards (red) show one real error each — the code that causes it, the traceback, why, and the fix. Module 11 collects all of them into one index.
Quick checks are one question each. Get one wrong and the explanation tells you which idea to re-read.
The learning board (bottom-left pill) has the roadmap, this module's lessons and errors, and a tutor that can see the code you last edited.
The handbook ends with a certification exam (Module 15 → exam), then the ATS resume checker and the job board. That is the whole point: from print() to a job.

A pace that works

One module a day, every day, beats a weekend binge. Each module is 60–90 minutes if you run everything. The streak counter in the hero exists for exactly this reason.

Using AI to learn (without cheating yourself)

You have an AI assistant that can write any of this code for you. Used well, it makes you learn faster than any previous generation could. Used badly, it produces people who can prompt for a program and cannot read one — and interviews find that out in ten minutes. The rule is simple: the AI explains, you type.

Learning nothing

"Write a function that counts words in a file" → paste → move on
Pasting an error and pasting the fix back without reading either
Asking for the answer to an exercise

Learning fast

"I wrote this — why does it print None?" (paste your own code)
"Explain this traceback line by line" — then fix it yourself
"Give me three exercises on dictionaries, no solutions"
"Is there a more Pythonic way to write this?" after it already works

The tutor in the learning board is built this way on purpose: it can see the code you edited and explain it, but it gives short examples, not finished programs. Every run block here is also a place to test what an AI told you — models are confidently wrong about Python more often than you would think, and running the code is the only referee.

pythonEdit it. ⌘/Ctrl + Enter runs.

# An AI once told a learner this returns 3. Does it?
numbers = [1, 2, 3]
result = numbers.append(4)
print(result)
print(numbers)

You should see

None
[1, 2, 3, 4]

Your turn

Before you run it: what do you think prints? append changes the list in place and returns None — one of the most common surprises in Python, and the reason to always run the code.

Module 01 →Fundamentals

Every lesson in the handbook

16 modules · 94 lessons · each one ticks itself when you reach the end or run its code.

00Getting Started0 / 6

Why Python Running Python — in this page and on your machine Your first program: add two numbers Comments How this handbook works Using AI to learn (without cheating yourself)

01Fundamentals0 / 6

Variables, literals and types Type conversion Input and output Operators Precedence and associativity Keywords and identifiers

02Flow Control0 / 5

if, elif, else for loops while loops break, continue and pass match / case (structural pattern matching)

03Data Types0 / 7

Numbers and math Strings Lists Tuples Sets Dictionaries Choosing the right one

04Functions0 / 6

Defining and calling functions Arguments and default values *args and **kwargs Scope: where a name lives Recursion Lambda

05Modules & Packages0 / 5

Modules and import Packages if __name__ == "__main__"pip and virtual environments Standard library tour

06Files & Data0 / 5

Reading and writing files Paths and directories with pathlib CSV — reading and writing JSON Text, bytes and encodings

07Exceptions0 / 5

What an exception is try / except / else / finally Raising, and custom exceptions assert Reading a traceback (bottom-up)

08Objects & Classes0 / 7

Classes and objects Inheritance and super()Multiple inheritance and the MRO Polymorphism and duck typing Operator overloading: dunder methods @property dataclasses

09Advanced Python0 / 6

Comprehensions Iterators and the iterator protocol Generators Closures Decorators Type hints

10Regex, Date & Time0 / 5

Regular expressions datetime: dates, times and arithmetic Formatting and parsing: strftime and strptime Timestamps and time zones The time module and sleep

11Errors & Debugging0 / 6

Anatomy of a traceback The 15 errors every beginner hits print debugging, then logging breakpoint() and pdb Reading errors from inside libraries "It works on my machine"

12Problem Solving0 / 7

How to read a problem Big-O in plain English Pattern 1 & 2: two pointers, sliding window Pattern 3 & 4: hashmap, stack Pattern 5 & 6: recursion / backtracking, sorting Pattern 7 & 8: BFS / DFS, dynamic programming Worked examples: from statement to solution

13Python + Tools0 / 9

Python + SQL Python + pandas Python + FastAPI Python + HTTP APIs (requests)Python + Docker Python + AWS (boto3)Python + Spark (PySpark)Python + Airflow Python + Git

14Interview Questions0 / 5

Junior — 25 questions Mid-level — 25 questions Senior — 10 questions The coding round, walked through Take-home assignment checklist

15Job Ready0 / 4

What a Python resume must show Portfolio: three projects that get callbacks Where the jobs are, and how to read a posting Certification exam → certificate

Frequently asked questions

Is this Python handbook free?

Yes — every module, every runnable example and the certification exam are free, with no signup and no paywall. The exam asks you to sign in with Google so the certificate can carry your name.

Do I need to install Python?

No. Every example runs inside your browser: press Run and a full CPython interpreter (Pyodide) is downloaded once, then everything executes locally. Nothing you type is sent to a server. Module 00 also shows you how to install Python on your own machine for when you want to build real projects.

How long does it take?

Reading and running the sixteen modules takes roughly 20 to 25 hours. Most people do a module a day. The lessons tick themselves as you go, so you can stop and resume where you left off.

What is different from Programiz or W3Schools?

They teach syntax; this handbook also teaches the fifteen errors every beginner hits and why the interpreter says them, a line-by-line trace of what actually happened, eight problem-solving patterns, Python with SQL, pandas, FastAPI, Docker and AWS, sixty interview questions by level, and a job-ready module that ends at the ATS resume checker and the job board.

Which Python version?

Python 3.13 runs in your browser here, and everything taught is valid on any Python 3.10 or newer, including match statements and modern type hints.

Is there a certificate?

Yes. Pass the 25-question exam with 70% or more and generate a SolutionGigs Python certificate with your name, score, date and a certificate ID — download it, print it or add it to LinkedIn.

Finish the Python handbook, then get hired

Sit the exam for your certificate, run your resume through the ATS checker, and see the jobs that ask for exactly this.

Check my resume

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