Compare labels edge by edge without relying on total order.

Author: novoselt

src/sage/graphs/generic_graph.py

@@ -474,28 +474,33 @@ def __eq__(self, other):
             return False
         # Finally, we are prepared to check edges:
         if not self.allows_multiple_edges():
-            return all(other.has_edge(*edge) for edge in self.edge_iterator(
-                                    labels=self._weighted))
-        else:
-            ii = jj = None
-            for i,j in self.edge_iterator(labels = False):
-                if i == ii and j == jj:
-                    continue
-                ii = i
-                jj = j
-
-                # The labels of edge ij in each graph
-                labels1 =  self.edge_label(i, j)
-                try:
-                    labels2 = other.edge_label(i, j)
-                except LookupError:
-                    return False
-
-                if len(labels1) != len(labels2):
-                    return False
-                if self._weighted and sorted(labels1) != sorted(labels2):
-                    return False
-            return True
+            return all(other.has_edge(*edge)
+                       for edge in self.edge_iterator(labels=self._weighted))
+        # The problem with multiple edges is that labels may not have total
+        # ordering, which makes it difficult to compare lists of labels.
+        last_i = last_j = None
+        for i, j in self.edge_iterator(labels=False):
+            if i == last_i and j == last_j:
+                continue
+            last_i, last_j = i, j
+            # All labels between i and j
+            labels1 = self.edge_label(i, j)
+            try:
+                labels2 = other.edge_label(i, j)
+            except LookupError:
+                return False
+            if len(labels1) != len(labels2):
+                return False
+            if self._weighted:
+                # If there is total ordering, sorting will speed up things
+                labels1.sort()
+                labels2.sort()
+                for l in labels1:
+                    try:
+                        labels2.remove(l)
+                    except ValueError:
+                        return False
+        return True
 
     @cached_method
     def __hash__(self):