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Python output prediction practice

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How this archive works

Every card is a "predict the output" question — the exact format used in Python interviews and university exams. The featured questions below run right on the page: type your predicted output, check it, and get a line-by-line trace of why. The rest open in PyDebug's interactive editor, which verifies your prediction automatically.

New to the format? Start with the output-prediction strategy guide, then come back and drill.

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Answer on this page

Print a list slice

Three slices of the same five-element list. Every one of them is governed by a single rule — slices include th…

lists easy

for loop with range and step

Two rules interact here: what range(1, 10, 3) actually generates, and what the loop variable holds after the l…

loops medium

String multiplication

String multiplication repeats the whole string — and every later line operates on the result, not the original…

strings easy

Answer in the interactive editor

break vs continue

Interactive — predict in the editor, get checked instantly.

loops medium

Loop variable after the loop ends

Interactive — predict in the editor, get checked instantly.

loops medium

else clause on a for loop

Interactive — predict in the editor, get checked instantly.

loops medium

enumerate with a start value

Interactive — predict in the editor, get checked instantly.

loops easy

List multiplication

Interactive — predict in the editor, get checked instantly.

lists medium

Negative indexing

Interactive — predict in the editor, get checked instantly.

lists easy

List copy vs reference

Interactive — predict in the editor, get checked instantly.

lists easy

Slicing excludes the end index

Interactive — predict in the editor, get checked instantly.

lists easy

String repetition and length

Interactive — predict in the editor, get checked instantly.

strings easy

String multiplication and indexing

Interactive — predict in the editor, get checked instantly.

strings easy

String multiplication in a loop

Interactive — predict in the editor, get checked instantly.

strings medium

Default parameter values

Interactive — predict in the editor, get checked instantly.

functions medium

Function returning nothing

Interactive — predict in the editor, get checked instantly.

functions easy

Chained assignment

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functions easy

Mutable default argument trap

Interactive — predict in the editor, get checked instantly.

functions medium

dict.get() with a default

Interactive — predict in the editor, get checked instantly.

dictionaries medium

Dictionary keys must be unique

Interactive — predict in the editor, get checked instantly.

dictionaries medium

Tuple immutability

Interactive — predict in the editor, get checked instantly.

tuples easy

Sets remove duplicates

Interactive — predict in the editor, get checked instantly.

sets easy

try/except/else flow

Interactive — predict in the editor, get checked instantly.

exceptions medium

Class variable shared across instances

Interactive — predict in the editor, get checked instantly.

oop medium

Why output prediction makes you a better debugger

Debugging is prediction in reverse: you read code that already misbehaved and reconstruct what it must have done. Practising forward prediction — stating exactly what each line prints before running it — builds the same mental interpreter. The learners who get fast at these questions are the same ones who stop needing twenty print statements to find a bug.

Struggling with a specific crash instead? The Python error explainer decodes the six most common exceptions, and the tricks collection catalogues the classic traps.