sorts: type shell_sort for comparable items and add tests

sorts/shell_sort.py

@@ -2,8 +2,15 @@
 https://en.wikipedia.org/wiki/Shellsort#Pseudocode
 """
 
+from collections.abc import MutableSequence
+from typing import Any, Protocol
 
-def shell_sort(collection: list[int]) -> list[int]:
+
+class Comparable(Protocol):
+    def __lt__(self, other: Any, /) -> bool: ...
+
+
+def shell_sort[T: Comparable](collection: MutableSequence[T]) -> MutableSequence[T]:
     """Pure implementation of shell sort algorithm in Python
     :param collection:  Some mutable ordered collection with heterogeneous
     comparable items inside
@@ -15,6 +22,15 @@ def shell_sort(collection: list[int]) -> list[int]:
     []
     >>> shell_sort([-2, -5, -45])
     [-45, -5, -2]
+    >>> shell_sort(["c", "a", "b"])
+    ['a', 'b', 'c']
+    >>> shell_sort([2.5, -1, 0.0])
+    [-1, 0.0, 2.5]
+    >>> shell_sort(["c", "a", "b"]) == sorted(["c", "a", "b"])
+    True
+    >>> import pytest
+    >>> with pytest.raises(TypeError):
+    ...     shell_sort([1, "a"])
     """
     # Marcin Ciura's gap sequence
 

tests/test_sorts.py

@@ -121,6 +121,7 @@ def test_sort_matches_builtin(sort, case):
         insertion_sort,
         merge_sort,
         selection_sort,
+        shell_sort,
     ],
     ids=lambda f: f.__name__,
 )