Add method to return edge indices from endpoints (#1055)

* add edge_indices_from_endpoints for graph and digraph

* fix tests

* Add release notes

* linter

* black

* Fix text_signature for new method

---------

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

releasenotes/notes/add-edge_indices_from_endpoints-method-to-graph-d58dc98719c4db39.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Added method :meth:`~rustworkx.PyGraph.edge_indices_from_endpoints` which returns the indices of all edges
+    between the specified endpoints. For :class:`~rustworkx.PyDiGraph` there is a corresponding method that returns the 
+    directed edges.

rustworkx/digraph.pyi

@@ -68,6 +68,7 @@ class PyDiGraph(Generic[S, T]):
     def copy(self) -> PyDiGraph[S, T]: ...
     def edge_index_map(self) -> EdgeIndexMap[T]: ...
     def edge_indices(self) -> EdgeIndices: ...
+    def edge_indices_from_endpoints(self, node_a: int, node_b: int) -> EdgeIndices: ...
     def edge_list(self) -> EdgeList: ...
     def edges(self) -> list[T]: ...
     def edge_subgraph(self, edge_list: Sequence[tuple[int, int]], /) -> PyDiGraph[S, T]: ...

rustworkx/graph.pyi

@@ -66,6 +66,7 @@ class PyGraph(Generic[S, T]):
     def degree(self, node: int, /) -> int: ...
     def edge_index_map(self) -> EdgeIndexMap[T]: ...
     def edge_indices(self) -> EdgeIndices: ...
+    def edge_indices_from_endpoints(self, node_a: int, node_b: int) -> EdgeIndices: ...
     def edge_list(self) -> EdgeList: ...
     def edges(self) -> list[T]: ...
     def edge_subgraph(self, edge_list: Sequence[tuple[int, int]], /) -> PyGraph[S, T]: ...

src/digraph.rs

@@ -547,6 +547,24 @@ impl PyDiGraph {
         }
     }
 
+    /// Return a list of indices of all directed edges between specified nodes
+    ///
+    /// :returns: A list of all the edge indices connecting the specified start and end node
+    /// :rtype: EdgeIndices
+    pub fn edge_indices_from_endpoints(&self, node_a: usize, node_b: usize) -> EdgeIndices {
+        let node_a_index = NodeIndex::new(node_a);
+        let node_b_index = NodeIndex::new(node_b);
+
+        EdgeIndices {
+            edges: self
+                .graph
+                .edges_directed(node_a_index, petgraph::Direction::Outgoing)
+                .filter(|edge| edge.target() == node_b_index)
+                .map(|edge| edge.id().index())
+                .collect(),
+        }
+    }
+
     /// Return a list of all node data.
     ///
     /// :returns: A list of all the node data objects in the graph

src/graph.rs

@@ -422,6 +422,24 @@ impl PyGraph {
         }
     }
 
+    /// Return a list of indices of all edges between specified nodes
+    ///
+    /// :returns: A list of all the edge indices connecting the specified start and end node
+    /// :rtype: EdgeIndices
+    pub fn edge_indices_from_endpoints(&self, node_a: usize, node_b: usize) -> EdgeIndices {
+        let node_a_index = NodeIndex::new(node_a);
+        let node_b_index = NodeIndex::new(node_b);
+
+        EdgeIndices {
+            edges: self
+                .graph
+                .edges_directed(node_a_index, petgraph::Direction::Outgoing)
+                .filter(|edge| edge.target() == node_b_index)
+                .map(|edge| edge.id().index())
+                .collect(),
+        }
+    }
+
     /// Return a list of all node data.
     ///
     /// :returns: A list of all the node data objects in the graph

tests/rustworkx_tests/digraph/test_edges.py

@@ -370,6 +370,25 @@ def test_weighted_edge_list_empty(self):
         dag = rustworkx.PyDiGraph()
         self.assertEqual([], dag.weighted_edge_list())
 
+    def test_edge_indices_from_endpoints(self):
+        dag = rustworkx.PyDiGraph()
+        dag.add_nodes_from(list(range(4)))
+        edge_list = [
+            (0, 1, None),
+            (1, 2, None),
+            (0, 2, None),
+            (2, 3, None),
+            (0, 3, None),
+            (0, 2, None),
+        ]
+        dag.add_edges_from(edge_list)
+        indices = dag.edge_indices_from_endpoints(0, 0)
+        self.assertEqual(indices, [])
+        indices = dag.edge_indices_from_endpoints(0, 1)
+        self.assertEqual(indices, [0])
+        indices = dag.edge_indices_from_endpoints(0, 2)
+        self.assertEqual(set(indices), {2, 5})
+
     def test_extend_from_edge_list(self):
         dag = rustworkx.PyDAG()
         edge_list = [(0, 1), (1, 2), (0, 2), (2, 3), (0, 3)]

tests/rustworkx_tests/graph/test_edges.py

@@ -331,6 +331,26 @@ def test_weighted_edge_list_empty(self):
         graph = rustworkx.PyGraph()
         self.assertEqual([], graph.weighted_edge_list())
 
+    def test_edge_indices_from_endpoints(self):
+        dag = rustworkx.PyGraph()
+        dag.add_nodes_from(list(range(4)))
+        edge_list = [
+            (0, 1, None),
+            (1, 2, None),
+            (0, 2, None),
+            (2, 3, None),
+            (0, 3, None),
+            (0, 2, None),
+            (2, 0, None),
+        ]
+        dag.add_edges_from(edge_list)
+        indices = dag.edge_indices_from_endpoints(0, 0)
+        self.assertEqual(indices, [])
+        indices = dag.edge_indices_from_endpoints(0, 1)
+        self.assertEqual(set(indices), {0})
+        indices = dag.edge_indices_from_endpoints(0, 2)
+        self.assertEqual(set(indices), {2, 5, 6})
+
     def test_extend_from_edge_list(self):
         graph = rustworkx.PyGraph()
         edge_list = [(0, 1), (1, 2), (0, 2), (2, 3), (0, 3)]