Python output prediction practice

dict.get() vs [key]

A missing key is a KeyError with brackets and None with get(). Plus what len() and pop() report after setdefault adds a key.

finally Before return

A finally block runs even when the try block returns — and it runs before the returned value reaches the caller. Two verified traces.

Mutable Default Argument

A list default argument is created once, not per call — so the second call sees the first call's items. Verified output plus a…

Python List Slicing

Predict what three print() calls with list slices output — nums[1:4], nums[-2:], nums[::2]. Type your answer, reveal the result, and read a…

Shared List References

Two names, one list: why changing one row of a built grid changes the other, and why list.copy() still is not enough for nested lists.

sort() vs sorted()

sorted() returns a new list once — appending afterwards does not re-sort it. Compare sort() and sorted() before an exam question traps you.

Why append() Returns None

list.append() changes the list and hands back None. Print the result of either line and see why chained 'x = y.append(…)' wipes a…

for Loop With range()

A for loop over range(1, 10, 3) with a running total — predict every printed line including the one after the loop. Answer reveal with a…

// and % With Negatives

Floor division rounds down, not toward zero — which is why -7 // 2 is -4 and -7 % 2 is still 1. The rule that fixes both signs at once.

Why 0.1 + 0.2 Is Not 0.3

Binary floats cannot hold 0.1 exactly, so 0.1 + 0.2 prints 0.30000000000000004 and round(2.675, 2) goes down. Real output, plus Decimal.

Truthiness and the Ternary

0 is false but '0' is true, empty lists are false, and not/and/or return objects instead of booleans. Verified output with the…

How a Set Deduplicates

1, 1.0 and True are one member, not three — and set order is not insertion order. Verified output with the hash rule behind it.

Negative Indexes and Slices

Three slice expressions on 'python' — negative stop, a reversed slice chained with another slice, and why the end index never…

Python String Multiplication

word * 3, len() of the result, indexing into it, and the '' * 0 edge case — four prints to predict, then a full line-by-line…

The One-Element Tuple Comma

Parentheses do not make a tuple — the comma does. See why (1) is an int, (1,) * 2 differs from 1 * 2, and unpacking needs that comma.

break vs continue

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Loop variable after the loop ends

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else clause on a for loop

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enumerate with a start value

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List multiplication

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Negative indexing

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List copy vs reference

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Slicing excludes the end index

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String repetition and length

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String multiplication and indexing

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String multiplication in a loop

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Default parameter values

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Function returning nothing

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Chained assignment

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Mutable default argument trap

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dict.get() with a default

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Dictionary keys must be unique

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Tuple immutability

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Sets remove duplicates

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try/except/else flow

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Class variable shared across instances

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