From c789b2fdb145d940cbb30803338d1cc969dca5b5 Mon Sep 17 00:00:00 2001
From: taljeon <taljeon@users.noreply.github.com>
Date: Tue, 15 Sep 2026 05:06:21 +0900
Subject: [PATCH] sorts: type shrink shell sort for comparable items

---
 sorts/shrink_shell_sort.py | 16 +++++++++++++++-
 tests/test_sorts.py        |  3 +++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/sorts/shrink_shell_sort.py b/sorts/shrink_shell_sort.py
index f77b73d013a7..f6736364daf1 100644
--- a/sorts/shrink_shell_sort.py
+++ b/sorts/shrink_shell_sort.py
@@ -20,8 +20,14 @@
 using a smaller gap, the list is sorted more quickly.
 """
 
+from typing import Protocol
 
-def shell_sort(collection: list) -> list:
+
+class Comparable(Protocol):
+    def __lt__(self, other: object, /) -> bool: ...
+
+
+def shell_sort[T: Comparable](collection: list[T]) -> list[T]:
     """Implementation of shell sort algorithm in Python
     :param collection:  Some mutable ordered collection with heterogeneous
     comparable items inside
@@ -33,6 +39,14 @@ def shell_sort(collection: list) -> list:
     []
     >>> shell_sort([1])
     [1]
+    >>> shell_sort(["pear", "apple", "orange"])
+    ['apple', 'orange', 'pear']
+    >>> shell_sort([2.5, -1, 0.0])
+    [-1, 0.0, 2.5]
+    >>> shell_sort([1, "a"])  # doctest: +IGNORE_EXCEPTION_DETAIL
+    Traceback (most recent call last):
+        ...
+    TypeError: ...
     """
 
     # Choose an initial gap value
diff --git a/tests/test_sorts.py b/tests/test_sorts.py
index 2c9b79aa4bfe..75856cebadb4 100644
--- a/tests/test_sorts.py
+++ b/tests/test_sorts.py
@@ -37,6 +37,7 @@
 from sorts.quick_sort import quick_sort
 from sorts.selection_sort import selection_sort
 from sorts.shell_sort import shell_sort
+from sorts.shrink_shell_sort import shell_sort as shrink_shell_sort
 from sorts.stooge_sort import stooge_sort
 from sorts.strand_sort import strand_sort
 
@@ -68,6 +69,7 @@ def test_heap_sort() -> None:
     quick_sort,
     selection_sort,
     shell_sort,
+    shrink_shell_sort,
     stooge_sort,
     strand_sort,
 )
@@ -122,6 +124,7 @@ def test_sort_matches_builtin(sort, case) -> None:
         insertion_sort,
         merge_sort,
         selection_sort,
+        shrink_shell_sort,
     ],
     ids=lambda f: f.__name__,
 )