fix(sorts): accept lt-only items in recursive insertion sort

sorts/recursive_insertion_sort.py

@@ -5,17 +5,14 @@
 from __future__ import annotations
 
 from collections.abc import MutableSequence
-from typing import Any, Protocol, TypeVar
+from typing import Protocol
 
 
 class Comparable(Protocol):
-    def __lt__(self, other: Any, /) -> bool: ...
+    def __lt__(self, other: object, /) -> bool: ...
 
 
-T = TypeVar("T", bound=Comparable)
-
-
-def rec_insertion_sort[T](collection: MutableSequence[T], n: int) -> None:
+def rec_insertion_sort[T: Comparable](collection: MutableSequence[T], n: int) -> None:
     """
     Given a collection of comparable elements and its length, sorts the
     collection in place in ascending order.
@@ -51,7 +48,7 @@ def rec_insertion_sort[T](collection: MutableSequence[T], n: int) -> None:
     rec_insertion_sort(collection, n - 1)
 
 
-def insert_next[T](collection: MutableSequence[T], index: int) -> None:
+def insert_next[T: Comparable](collection: MutableSequence[T], index: int) -> None:
     """
     Inserts the '(index-1)th' element into place
 
@@ -71,7 +68,7 @@ def insert_next[T](collection: MutableSequence[T], index: int) -> None:
     []
     """
     # Checks order between adjacent elements
-    if index >= len(collection) or collection[index - 1] <= collection[index]:
+    if index >= len(collection) or not collection[index] < collection[index - 1]:
         return
 
     # Swaps adjacent elements since they are not in ascending order

tests/test_sorts.py

@@ -186,6 +186,20 @@ def test_rec_insertion_sort_rejects_non_comparable_items() -> None:
         rec_insertion_sort([1, "a"], 2)
 
 
+def test_rec_insertion_sort_lt_only_items() -> None:
+    class LessOnly:
+        def __init__(self, value: int) -> None:
+            self.value = value
+
+        def __lt__(self, other: object) -> bool:
+            assert isinstance(other, LessOnly)
+            return self.value < other.value
+
+    collection = [LessOnly(3), LessOnly(1), LessOnly(2)]
+    rec_insertion_sort(collection, len(collection))
+    assert [item.value for item in collection] == [1, 2, 3]
+
+
 def test_bogo_sort_comparable_items() -> None:
     assert bogo_sort(["c", "a", "b"]) == ["a", "b", "c"]
     assert bogo_sort([2.5, -1.0, 0.0]) == [-1.0, 0.0, 2.5]