Python 101 — Fundamentals

Welcome to Python 101

If you have shipped TypeScript, you already know more Python than you think. Both languages are dynamically typed at their core (TypeScript adds a compile-time type layer; Python 3 adds optional hints), both are garbage-collected, and both lean on expressive syntax over ceremony. The biggest mental shift is cosmetic: indentation replaces curly braces, and a lot of JavaScript’s syntactic sugar has a cleaner Python equivalent.

This module walks you through nine lessons, each anchored in code you already know. You will leave with enough Python to read real projects, write scripts, and build REST APIs with FastAPI.

A quick taste: the same program in both languages

Here is a tiny program — a list of names filtered and greeted — written first in TypeScript, then in Python. Same logic, same output, different syntax.

TypeScript

const names: string[] = ["Alice", "Bob", "Carol", "Dave"];

const short = names.filter((n) => n.length <= 4);

for (const name of short) {
  console.log(`Hello, ${name}!`);
}

// Hello, Bob!
// Hello, Dave!

Python

names: list[str] = ["Alice", "Bob", "Carol", "Dave"]

short = [n for n in names if len(n) <= 4]

for name in short:
    print(f"Hello, {name}!")

# Hello, Bob!
# Hello, Dave!

Try it

Run ▸ Open in an online REPL

names: list[str] = ["Alice", "Bob", "Carol", "Dave"]

short = [n for n in names if len(n) <= 4]

for name in short:
    print(f"Hello, {name}!")

What you will learn

Lesson	You already know (TS)	You will learn (Python)
Variables	let / const + static types	Dynamic typing, type hints, UPPER_CASE constants
Functions	Arrow & function	def, default args, keyword args, *args/**kwargs
Control Flow	if/else, for, switch	if/elif, for...in, match/case
Collections	Array, object, Map, Set	list, tuple, dict, set, slicing
Classes	class, constructor, this	class, __init__, self, dunders
Modules	ESM import/export, npm	import, from ... import, pip
Errors	try/catch/finally	try/except/else/finally, raise
None & Truthiness	null, undefined, falsy values	None, is None, Python truthiness

What replaces curly braces to define code blocks in Python?

Parentheses Indentation Brackets BEGIN/END keywords

Python type hints (e.g. `name: str`) are enforced at:

Compile time Import time Runtime by the interpreter They are not enforced by the interpreter

Which Python construct is the closest equivalent of a TypeScript `Array.filter()` one-liner?

A generator expression A list comprehension A `map()` call A `filter()` call with `list()`

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