Preserve key type for Optional defaults

schema/__init__.py

@@ -905,7 +905,15 @@ def __init__(self, *args: Any, **kwargs: Any) -> None:
                     f'"{self._schema!r}" is too complex.'
                 )
             self.default = default
-            self.key = str(self._schema)
+            # Preserve the original key object so the default fills the output
+            # under the same key (and key type) that a present key would use.
+            # Stringifying here made an absent optional produce ``str(key)``
+            # (e.g. ``"5"``) while a present key kept its real type (``5``).
+            self.key = (
+                self._schema.schema
+                if isinstance(self._schema, Literal)
+                else self._schema
+            )
 
     def __hash__(self) -> int:
         return hash(self._schema)

test_schema.py

@@ -419,6 +419,17 @@ def test_dict_optional_defaults():
         Optional(And(str, Use(int)), default=7)
 
 
+def test_dict_optional_default_preserves_key_type():
+    # A non-string key must keep its type when the default fills it in, just
+    # as it does when the key is present in the data.
+    for key in (5, None, 1.5):
+        schema = Schema({Optional(key, default="x"): str})
+        assert schema.validate({}) == {key: "x"}
+        # present and absent must agree on the output key type
+        present = {key: "p"}
+        assert schema.validate(present) == present
+
+
 def test_dict_subtypes():
     d = defaultdict(int, key=1)
     v = Schema({"key": 1}).validate(d)