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Python practice

Aliasing

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What does this print?

grid = [[0] * 2] * 2 grid[0][0] = 1 print(grid)

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No signup · first signal after 5 answers · your score at session end

Predict the output — and learn why Python does that

Master Python by predicting what real code prints — slicing and negative indices, list and dict comprehensions, integer floor division and modulo signs, mutability and aliasing traps (including the classic mutable-default-argument bug), truthiness and and/or short-circuiting, and the built-ins. Every answer is computed by running real CPython, so the explanations are exact. Output-prediction practice that builds genuine fluency for interviews. Part of the Developer track.

• Meets you at your level — never too easy, never too hard.

• Adapts every question to how you’re doing.

• Tracks your level over time. Skill practice, not a test.

New here? Read the Python guide

A free 18-minute primer — the mental model, the mistakes beginners make, and what to practice first.

Curriculum

249 concepts across 23 chapters, from foundations through advanced practice — each one a concept the adaptive question bank can teach and test.

A. Objects, names and the data model

B. Numbers and arithmetic

C. Sequences: list, tuple, range

D. Strings and text

E. Bytes and binary data

F. Dicts, sets and hashing

G. Control flow and comprehensions

H. Functions, arguments and scope

I. Closures, decorators and functools

J. Iterators, generators and itertools

K. Classes, attributes and descriptors

L. Dataclasses, enums and records

M. Exceptions and error handling

N. Context managers and resource cleanup

O. Modules, packages and imports

P. Typing and annotations

Q. Concurrency: threads, processes and the GIL

R. asyncio and async/await

S. Files, paths and I/O

T. Standard-library toolkit

U. Testing, debugging and performance

V. Packaging, environments and tooling

W. Language evolution and version gates

View the full curriculum →

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Start practicing — it’s free

No signup · first signal after 5 answers · your score at session end

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Python on exams

Python is one of the skills tested on these exams. Each prep page lays out what the real test covers and where this skill fits.

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