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test: cover insertion sort stability with equal-priority items #15480

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test: cover insertion sort stability with equal-priority items #15480

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11 changes: 11 additions & 0 deletions sorts/insertion_sort.py
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,17 @@ def insertion_sort[T: Comparable](collection: MutableSequence[T]) -> MutableSequ
True
>>> values
[1, 2, 4, 7]

Equal-priority items retain their original relative order:
>>> from dataclasses import dataclass, field
>>> @dataclass(order=True)
... class Item:
... priority: int
... label: str = field(compare=False)
>>> items = [Item(2, "A"), Item(1, "X"), Item(2, "B"), Item(1, "Y")]
>>> [(item.priority, item.label) for item in insertion_sort(items)]

@cclauss cclauss Oct 3, 2026 •
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Use @dataclass(order=True) so you can just insertion_sort(items) instead of adding an extra list comprehension.

Python/tests/test_sorts.py

Lines 134 to 137 in 84b73d0

@dataclass(order=True)
class Person:
name: str = "Bob"
age: int = 37

[(1, 'X'), (1, 'Y'), (2, 'A'), (2, 'B')]

>>> import random
>>> collection = random.sample(range(-50, 50), 100)
>>> insertion_sort(collection) == sorted(collection)
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