Add schema.asdict

Author: benjeffery

python/tests/test_metadata.py

@@ -347,11 +347,15 @@ def test_parse(self):
         ms = metadata.parse_metadata_schema("")
         assert isinstance(ms, metadata.MetadataSchema)
         assert ms.schema is None
+        assert ms.asdict() is None
 
         # json gives MetaDataSchema with json codec
         ms = metadata.parse_metadata_schema(json.dumps({"codec": "json"}))
         assert isinstance(ms, metadata.MetadataSchema)
         assert ms.schema == {"codec": "json"}
+        assert ms.asdict() == {"codec": "json"}
+        # check we get a copy
+        assert ms.asdict() is not ms._schema
 
         # Bad JSON gives error
         with pytest.raises(ValueError):

python/tskit/metadata.py

@@ -548,8 +548,16 @@ def __eq__(self, other) -> bool:
 
     @property
     def schema(self) -> Optional[Mapping[str, Any]]:
-        # Make schema read-only
-        return self._schema
+        # Return a copy to avoid unintentional mutation
+        return copy.deepcopy(self._schema)
+
+    def asdict(self) -> Optional[Mapping[str, Any]]:
+        """
+        Returns a dict representation of this schema. One possible use of this is to
+        modify this dict and then pass it to the ``MetadataSchema`` constructor to create
+        a similar schema.
+        """
+        return self.schema
 
     def validate_and_encode_row(self, row: Any) -> bytes:
         """