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 +597,22 @@ 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.
+
+    :param listed: List of string entries to modify
+    :param 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}"
+
+    listed = list(listed)
+    return f"{', '.join(str(x) for x in listed[:-1])}, {condition} {listed[-1]}"