feat(edge): show ↔ and → between the ends of an edge

examples/roads.ipynb

@@ -187,35 +187,35 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Edge{[Camooweal] -- [Mount Isa], cost=188}\n",
-      "Edge{[Mount Isa] -- [Cloncurry], cost=118}\n",
-      "Edge{[Cloncurry] -- [Hughenden], cost=401}\n",
-      "Edge{[Cloncurry] -- [Winton], cost=350}\n",
-      "Edge{[Hughenden] -- [Charters Towers], cost=248}\n",
-      "Edge{[Charters Towers] -- [Townsville], cost=135}\n",
-      "Edge{[Townsville] -- [Mackay], cost=388}\n",
-      "Edge{[Mackay] -- [Rockhampton], cost=334}\n",
-      "Edge{[Mackay] -- [Emerald], cost=384}\n",
-      "Edge{[Rockhampton] -- [Brisbane], cost=682}\n",
-      "Edge{[Rockhampton] -- [Emerald], cost=270}\n",
-      "Edge{[Brisbane] -- [Roma], cost=482}\n",
-      "Edge{[Roma] -- [Charleville], cost=266}\n",
-      "Edge{[Charleville] -- [Blackall], cost=305}\n",
-      "Edge{[Blackall] -- [Barcaldine], cost=106}\n",
-      "Edge{[Blackall] -- [Windorah], cost=530}\n",
-      "Edge{[Barcaldine] -- [Emerald], cost=307}\n",
-      "Edge{[Barcaldine] -- [Hughenden], cost=500}\n",
-      "Edge{[Barcaldine] -- [Longreach], cost=106}\n",
-      "Edge{[Longreach] -- [Windorah], cost=311}\n",
-      "Edge{[Longreach] -- [Winton], cost=180}\n",
-      "Edge{[Winton] -- [Hughenden], cost=216}\n",
-      "Edge{[Winton] -- [Boulia], cost=363}\n",
-      "Edge{[Winton] -- [Windorah], cost=487}\n",
-      "Edge{[Boulia] -- [Mount Isa], cost=304}\n",
-      "Edge{[Boulia] -- [Bedourie], cost=194}\n",
-      "Edge{[Bedourie] -- [Birdsville], cost=193}\n",
-      "Edge{[Birdsville] -- [Windorah], cost=380}\n",
-      "Edge{[Bedourie] -- [Windorah], cost=411}\n"
+      "Edge{[Camooweal] ↔ [Mount Isa], cost=188}\n",
+      "Edge{[Mount Isa] ↔ [Cloncurry], cost=118}\n",
+      "Edge{[Cloncurry] ↔ [Hughenden], cost=401}\n",
+      "Edge{[Cloncurry] ↔ [Winton], cost=350}\n",
+      "Edge{[Hughenden] ↔ [Charters Towers], cost=248}\n",
+      "Edge{[Charters Towers] ↔ [Townsville], cost=135}\n",
+      "Edge{[Townsville] ↔ [Mackay], cost=388}\n",
+      "Edge{[Mackay] ↔ [Rockhampton], cost=334}\n",
+      "Edge{[Mackay] ↔ [Emerald], cost=384}\n",
+      "Edge{[Rockhampton] ↔ [Brisbane], cost=682}\n",
+      "Edge{[Rockhampton] ↔ [Emerald], cost=270}\n",
+      "Edge{[Brisbane] ↔ [Roma], cost=482}\n",
+      "Edge{[Roma] ↔ [Charleville], cost=266}\n",
+      "Edge{[Charleville] ↔ [Blackall], cost=305}\n",
+      "Edge{[Blackall] ↔ [Barcaldine], cost=106}\n",
+      "Edge{[Blackall] ↔ [Windorah], cost=530}\n",
+      "Edge{[Barcaldine] ↔ [Emerald], cost=307}\n",
+      "Edge{[Barcaldine] ↔ [Hughenden], cost=500}\n",
+      "Edge{[Barcaldine] ↔ [Longreach], cost=106}\n",
+      "Edge{[Longreach] ↔ [Windorah], cost=311}\n",
+      "Edge{[Longreach] ↔ [Winton], cost=180}\n",
+      "Edge{[Winton] ↔ [Hughenden], cost=216}\n",
+      "Edge{[Winton] ↔ [Boulia], cost=363}\n",
+      "Edge{[Winton] ↔ [Windorah], cost=487}\n",
+      "Edge{[Boulia] ↔ [Mount Isa], cost=304}\n",
+      "Edge{[Boulia] ↔ [Bedourie], cost=194}\n",
+      "Edge{[Bedourie] ↔ [Birdsville], cost=193}\n",
+      "Edge{[Birdsville] ↔ [Windorah], cost=380}\n",
+      "Edge{[Bedourie] ↔ [Windorah], cost=411}\n"
      ]
     }
    ],

src/pgraph/PGraph.py

@@ -4265,6 +4265,9 @@ def __str__(self) -> str:
         :return: endpoints, cost and optional data
         :rtype: str
 
+        The endpoints are separated by ``→`` if the edge is in a directed graph
+        and by ``↔`` otherwise.
+
         .. runblock:: pycon
 
             >>> from pgraph import Vertex, Edge
@@ -4273,10 +4276,15 @@ def __str__(self) -> str:
             >>> e = Edge(v1, v2, cost=5.0, data="A to B")
             >>> str(e)
 
+        .. versionchanged:: 1.1
+            The separator was ``--`` or ``->``.  Output redirected to a file or pipe
+            under a legacy Windows code page (cp1252) can raise
+            ``UnicodeEncodeError``; set ``PYTHONUTF8=1`` to avoid it.
+
         :seealso: :meth:`__repr__`
         """
         graph = self.v1._graph if self.v1 is not None else None
-        arrow = "->" if graph is not None and graph.directed else "--"
+        arrow = "→" if graph is not None and graph.directed else "↔"
         cost_str = "None" if self.cost is None else f"{self.cost:.4g}"
         s = f"{self.__class__.__name__}{{{self.v1} {arrow} {self.v2}, cost={cost_str}}}"
         if self.data is not None:

tests/test_graph.py

@@ -81,7 +81,7 @@ def test_show_lists_vertices_and_edges(self):
                 "  b at [3 4] component=0",
                 "  c at [5 6] component=1",
                 "edges:",
-                "  Edge{[a] -- [b], cost=2.5}",
+                "  Edge{[a] ↔ [b], cost=2.5}",
             ],
         )
 

tests/test_unified_graph.py

@@ -251,14 +251,19 @@ def test_other_names_in_the_module_are_errors(self):
 
 class TestEdgeArrow(unittest.TestCase):
     def test_arrow_follows_the_graph(self):
-        for flag, arrow in ((False, "--"), (True, "->")):
+        for flag, expected in (
+            (False, "Edge{[a] ↔ [b], cost=3}"),
+            (True, "Edge{[a] → [b], cost=3}"),
+        ):
             g = Graph(directed=flag)
             a, b = g.add_vertex(name="a"), g.add_vertex(name="b")
-            self.assertIn(arrow, str(g.add_edge(a, b)))
+            e = g.add_edge(a, b, cost=3)
+            self.assertEqual(str(e), expected)
+            self.assertEqual(repr(e), expected)
 
     def test_a_standalone_edge_has_no_arrow_to_show(self):
         e = Edge(Vertex(name="a"), Vertex(name="b"), cost=1)
-        self.assertIn("--", str(e))
+        self.assertEqual(str(e), "Edge{[a] ↔ [b], cost=1}")
 
 
 if __name__ == "__main__":