Adding metadata to CurvedPolygon.

This is (for now) a private member intended to be used only for
testing purposes.

src/bezier/curved_polygon.py

@@ -127,16 +127,24 @@ class CurvedPolygon(object):
     Args:
         edges (Tuple[~bezier.curve.Curve, ...]): The boundary edges
             of the curved polygon.
-        kwargs: The only keyword argument accepted is ``_verify``, which is
-            a :class:`bool` indicating if the edges should be verified as
-            having shared endpoints. It defaults to :data:`True`.
+        kwargs: There are two keyword arguments accepted:
+
+            * ``metadata`` (:class:`~typing.Sequence`): A sequence of triples
+              associated with this curved polygon. This is intended to be used
+              by callers that have created a curved polygon as an intersection
+              between two B |eacute| zier surfaces.
+            * ``_verify`` (:class:`bool`): Indicates if the edges should be
+              verified as having shared endpoints. Defaults to :data:`True`.
+
+            Other keyword arguments specified will be silently ignored.
     """
 
-    __slots__ = ('_edges', '_num_sides')
+    __slots__ = ('_edges', '_num_sides', '_metadata')
 
     def __init__(self, *edges, **kwargs):
         self._edges = edges
         self._num_sides = len(edges)
+        self._metadata = kwargs.pop('metadata', None)
         if kwargs.pop('_verify', True):
             self._verify()
 

tests/unit/test_curved_polygon.py

@@ -56,6 +56,7 @@ def test_constructor(self):
         curved_poly = self._make_one(edge0, edge1)
         self.assertEqual(curved_poly._edges, (edge0, edge1))
         self.assertEqual(curved_poly._num_sides, 2)
+        self.assertIsNone(curved_poly._metadata)
 
     def test_constructor_without_verify(self):
         import bezier
@@ -67,6 +68,21 @@ def test_constructor_without_verify(self):
         curved_poly = self._make_one(edge0, _verify=False)
         self.assertEqual(curved_poly._edges, (edge0,))
         self.assertEqual(curved_poly._num_sides, 1)
+        self.assertIsNone(curved_poly._metadata)
+
+    def test_constructor_with_metadata(self):
+        import bezier
+
+        edge0 = bezier.Curve(self.NODES0, 2)
+        edge1 = bezier.Curve(self.NODES1, 2)
+        metadata = (
+            (0, 0.0, 0.5),
+            (4, 0.5, 1.0),
+        )
+        curved_poly = self._make_one(edge0, edge1, metadata=metadata)
+        self.assertEqual(curved_poly._edges, (edge0, edge1))
+        self.assertEqual(curved_poly._num_sides, 2)
+        self.assertEqual(curved_poly._metadata, metadata)
 
     def test__verify_too_few(self):
         with self.assertRaises(ValueError):