Python

The basics behind the syntax — mutability, scope, comprehensions, and the object model — not just how to write a for loop.

Start the course Practise this with real questions

In this course

Types, identity, and mutabilityis against ==, and why a list and a tuple behave so differently once you pass them around.7 min
Functions, arguments, and *args / **kwargsPositional against keyword arguments, star-unpacking, and what a decorator actually is.7 min
Lists, dicts, sets, and comprehensionsPicking the right container, and writing a comprehension that reads better than the loop it replaces.8 min
Classes, __init__, and the attributes that surprise peopleInstance attributes against class attributes, and the mutable class attribute that behaves like a global.7 min
Exceptions, and the with statement that always cleans uptry/except/else/finally in the order they actually run, and what a context manager guarantees.8 min
The data model — dunder methodsHow len, ==, +, sorted and print reach into your class, and the __eq__/__hash__ pairing that makes objects safe to use as keys.9 min
Dataclasses and type hintsWhat @dataclass writes for you, the frozen/order/compare switches that change it, and why a type hint is a promise nobody enforces at runtime.10 min
Iterators and generatorsThe two-method protocol behind every for loop, generators that run only when asked, and the one-pass rule that silently empties a second loop.9 min
Closures and decorators in depthnonlocal and the UnboundLocalError it prevents, functools.wraps, decorators that take arguments, and the order stacked decorators run in.10 min
Writing context managers, and chaining exceptionsThe __enter__/__exit__ protocol, how __exit__ can swallow an exception, the try/finally that @contextmanager needs, and raise ... from.10 min
Sorting with key functions, and the collections modulesorted against list.sort, key functions and stable multi-key sorts, and the Counter, defaultdict and deque that replace hand-written bookkeeping.9 min
Shallow copies, deep copies, and call by sharingWhy a copied list can still change under you, what deepcopy does that list() does not, the [[0] * 3] * 3 grid trap, and how arguments are really passed.8 min
Strings, bytes, encodings and formattingstr against bytes, what UTF-8 does to a string's length, mojibake and decode errors, Unicode normalisation, and the f-string format specs worth knowing.10 min
Modules, imports, and testing with pytestWhat import really does, why from-imports and mocks interact the way they do, circular imports, and the pytest features every interview assumes.11 min
The GIL, threads and processesWhat the GIL does and does not protect, why threads help I/O but not CPU-bound Python, when to reach for processes, and how executors order their results.11 min
async/await and asyncioCoroutines that do nothing until awaited, the single-threaded event loop, gather and TaskGroup, the blocking call that freezes everything, and timeouts that cancel.12 min