Introduce oxford comma function

src/molecule/config.py

@@ -281,7 +281,7 @@ def collection(self) -> CollectionData | None:
             LOG.warning(
                 "The detected galaxy.yml file (%s) is incomplete, missing %s",
                 galaxy_file,
-                missing_keys,
+                util.oxford_comma(missing_keys),
             )
             return None
 

src/molecule/util.py

@@ -597,3 +597,27 @@ def print_as_yaml(data: object) -> None:
     # https://github.com/Textualize/rich/discussions/990#discussioncomment-342217
     result = Syntax(code=safe_dump(data), lexer="yaml", background_color="default")
     console.print(result)
+
+
+def oxford_comma(listed: Iterable[bool | str | Path], condition: str = "and") -> str:
+    """Format a list into a sentence.
+
+    Args:
+        listed: List of string entries to modify
+        condition: String to splice into string, usually 'and'
+
+    Returns:
+        Modified string
+    """
+    match [f"'{entry!s}'" for entry in listed]:
+        case []:
+            return ""
+        case [one]:
+            return one
+        case [one, two]:
+            return f"{one} {condition} {two}"
+        case [*front, back]:
+            return f"{', '.join(s for s in front)}, {condition} {back}"
+        case _:
+            # This should be unreachable, but is included for completeness.
+            return ""

tests/unit/test_util.py

@@ -354,7 +354,7 @@ def test_abs_path_with_symlink() -> None:
 
 @pytest.mark.parametrize(
     ("a", "b", "x"),
-    [  # noqa: PT007
+    (
         # Base of recursion scenarios
         ({"key": 1}, {"key": 2}, {"key": 2}),
         ({"key": {}}, {"key": 2}, {"key": 2}),
@@ -368,7 +368,27 @@ def test_abs_path_with_symlink() -> None:
             {"a": 1, "b": [{"c": 3}], "d": {"e": "bbb"}},
             {"a": 1, "b": [{"c": 3}], "d": {"e": "bbb", "f": 3}},
         ),
-    ],
+    ),
 )
 def test_merge_dicts(a: MutableMapping, b: MutableMapping, x: MutableMapping) -> None:  # type: ignore[type-arg]  # noqa: D103
     assert x == util.merge_dicts(a, b)
+
+
+@pytest.mark.parametrize(
+    ("sequence", "output"),
+    (
+        ([], ""),
+        (["item1"], "'item1'"),
+        (["item1", False], "'item1' and 'False'"),
+        (["item1", False, Path()], "'item1', 'False', and '.'"),
+    ),
+    ids=("empty", "one", "two", "three"),
+)
+def test_oxford_comma(sequence: list[str], output: str) -> None:
+    """Test the oxford_comma function.
+
+    Args:
+        sequence: sequence of items.
+        output: expected output string.
+    """
+    assert util.oxford_comma(sequence) == output