Add metadata_bytes method to TableCollection

python/CHANGELOG.rst

@@ -2,6 +2,10 @@
 [X.X.X] - XXXX-XX-XX
 --------------------
 
+**Features**
+
+- :issue:`832` - Add ``metadata_bytes`` method to allow access to raw
+  TableCollection metadata (:user:`benjeffery`, :pr:`842`)
 
 --------------------
 [0.3.1] - 2020-09-04

python/tests/test_tables.py

@@ -2512,22 +2512,30 @@ def test_set_metadata(self):
         tc = tskit.TableCollection(1)
         # Default is empty bytes
         self.assertEqual(tc.metadata, b"")
+        self.assertEqual(tc.metadata_bytes, b"")
 
         tc.metadata_schema = self.metadata_schema
         md1 = self.metadata_example_data()
         md2 = self.metadata_example_data(val=2)
         # Set
         tc.metadata = md1
         self.assertEqual(tc.metadata, md1)
+        self.assertEqual(tc.metadata_bytes, tskit.canonical_json(md1).encode())
         # Overwrite
         tc.metadata = md2
         self.assertEqual(tc.metadata, md2)
+        self.assertEqual(tc.metadata_bytes, tskit.canonical_json(md2).encode())
         # Del should fail
         with self.assertRaises(AttributeError):
             del tc.metadata
+        with self.assertRaises(AttributeError):
+            del tc.metadata_bytes
         # None should fail
         with self.assertRaises(exceptions.MetadataValidationError):
             tc.metadata = None
+        # Setting bytes should fail
+        with self.assertRaises(AttributeError):
+            tc.metadata_bytes = b"123"
 
     def test_default_metadata_schema(self):
         # Default should allow bytes
@@ -2544,6 +2552,7 @@ def test_round_trip_metadata(self):
         tc.metadata_schema = self.metadata_schema
         tc.metadata = data
         self.assertDictEqual(tc.metadata, data)
+        self.assertEqual(tc.metadata_bytes, tskit.canonical_json(data).encode())
 
     def test_bad_metadata(self):
         metadata = self.metadata_example_data()

python/tskit/tables.py

@@ -2074,6 +2074,13 @@ def metadata(self, metadata: Any) -> None:
             metadata
         )
 
+    @property
+    def metadata_bytes(self) -> Any:
+        """
+        The raw bytes of metadata for this TableCollection
+        """
+        return self._ll_tables.metadata
+
     def asdict(self):
         """
         Returns a dictionary representation of this TableCollection.