intro_sort heap-sort fallback ignores start and end boundaries #15434

Repository commit

b3f113d

Python version (python --version)

Python 3.14.7

Dependencies version (pip freeze)

Not applicable — no third-party dependencies are required. The reproduction uses only Python’s standard library.

Expected behavior

The intro_sort() helper in sorts/intro_sort.py should sort only the
half-open range [start:end], leaving elements outside that range unchanged,
including when it switches to heap sort.

Reproduction:

from sorts.intro_sort import intro_sort

values = [100, 4, 3, 2, 1, -100]
result = intro_sort(values, start=1, end=5, size_threshold=2, max_depth=0)
print(result)

Expected output:

[100, 1, 2, 3, 4, -100]

Only indices 1 through 4 are requested to be sorted. Setting max_depth=0
forces the heap-sort fallback.

Actual behavior

Actual output:

[-100, 1, 2, 3, 4, 100]

The heap-sort fallback calls heap_sort(array) on the entire list, ignoring
start and end. Consequently, elements outside the requested range move.

This report concerns range handling in the intro_sort() helper. It does
not demonstrate incorrect whole-list ordering from the public sort() function.