sorts: type unknown_sort's merge_sort for any comparable item (#15426)

Part of #15234.

Author: Fayupable

sorts/unknown_sort.py

@@ -5,8 +5,14 @@
 already O(n)
 """
 
+from typing import Protocol
 
-def merge_sort(collection: list) -> list:
+
+class Comparable(Protocol):
+    def __lt__(self, other: object, /) -> bool: ...
+
+
+def merge_sort[T: Comparable](collection: list[T]) -> list[T]:
     """Pure implementation of the fastest merge sort algorithm in Python
 
     :param collection: some mutable ordered collection with heterogeneous
@@ -22,6 +28,17 @@ def merge_sort(collection: list) -> list:
 
     >>> merge_sort([-2, -5, -45])
     [-45, -5, -2]
+
+    >>> merge_sort(['d', 'a', 'b', 'e']) == sorted(['d', 'a', 'b', 'e'])
+    True
+
+    >>> merge_sort([1.1, 3.3, 5.5, 2.2, 4.4])
+    [1.1, 2.2, 3.3, 4.4, 5.5]
+
+    >>> merge_sort([1, "a"])  # doctest: +IGNORE_EXCEPTION_DETAIL
+    Traceback (most recent call last):
+        ...
+    TypeError: '<' not supported between instances of 'str' and 'int'
     """
     start, end = [], []
     while len(collection) > 1:

tests/test_sorts.py

@@ -51,6 +51,7 @@
 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
+from sorts.unknown_sort import merge_sort as unknown_sort
 
 
 def test_heap_sort() -> None:
@@ -89,6 +90,7 @@ def test_heap_sort() -> None:
     shrink_shell_sort,
     stooge_sort,
     strand_sort,
+    unknown_sort,
 )
 
 
@@ -160,6 +162,7 @@ def test_rec_insertion_sort(case) -> None:
         selection_sort,
         shrink_shell_sort,
         strand_sort,
+        unknown_sort,
     ],
     ids=lambda f: f.__name__,
 )