Merge pull request #755 from igraph/feat/is_biconnected

feat: is_biconnected()

Author: ntamas

src/_igraph/graphobject.c

@@ -1421,6 +1421,27 @@ PyObject *igraphmodule_Graph_is_connected(igraphmodule_GraphObject * self,
   Py_RETURN_FALSE;
 }
 
+/** \ingroup python_interface_graph
+ * \brief Decides whether a graph is biconnected.
+ * \return Py_True if the graph is biconnected, Py_False otherwise
+ * \sa igraph_is_biconnected
+ */
+PyObject *igraphmodule_Graph_is_biconnected(igraphmodule_GraphObject *self, PyObject* Py_UNUSED(_null))
+{
+  igraph_bool_t res;
+
+  if (igraph_is_biconnected(&self->g, &res)) {
+    igraphmodule_handle_igraph_error();
+    return NULL;
+  }
+
+  if (res) {
+    Py_RETURN_TRUE;
+  } else {
+    Py_RETURN_FALSE;
+  }
+}
+
 /** \ingroup python_interface_graph
  * \brief Decides whether there is an edge from a given vertex to an other one.
  * \return Py_True if the vertices are directly connected, Py_False otherwise
@@ -15275,6 +15296,20 @@ struct PyMethodDef igraphmodule_Graph_methods[] = {
    "@param mode: whether we should calculate strong or weak connectivity.\n"
    "@return: C{True} if the graph is connected, C{False} otherwise.\n"},
 
+  /* interface to igraph_is_biconnected */
+  {"is_biconnected", (PyCFunction) igraphmodule_Graph_is_biconnected,
+   METH_NOARGS,
+   "is_biconnected()\n--\n\n"
+   "Decides whether the graph is biconnected.\n\n"
+   "A graph is biconnected if it stays connected after the removal of\n"
+   "any single vertex.\n\n"
+   "Note that there are different conventions in use about whether to\n"
+   "consider a graph consisting of two connected vertices to be biconnected.\n"
+   "igraph does consider it biconnected.\n\n"
+   "@return: C{True} if it is biconnected, C{False} otherwise.\n"
+   "@rtype: boolean"
+  },
+
   /* interface to igraph_linegraph */
   {"linegraph", (PyCFunction) igraphmodule_Graph_linegraph,
    METH_VARARGS | METH_KEYWORDS,

tests/test_structural.py

@@ -242,6 +242,8 @@ class BiconnectedComponentTests(unittest.TestCase):
     g1 = Graph.Full(10)
     g2 = Graph(5, [(0, 1), (1, 2), (2, 3), (3, 4)])
     g3 = Graph(6, [(0, 1), (1, 2), (2, 3), (3, 0), (2, 4), (2, 5), (4, 5)])
+    g4 = Graph.Full(2)
+    g5 = Graph.Full(1)
 
     def testBiconnectedComponents(self):
         s = self.g1.biconnected_components()
@@ -260,6 +262,14 @@ def testArticulationPoints(self):
         self.assertTrue(self.g1.articulation_points() == [])
         self.assertTrue(self.g2.cut_vertices() == [1, 2, 3])
         self.assertTrue(self.g3.articulation_points() == [2])
+        self.assertTrue(self.g4.articulation_points() == [])
+
+    def testIsBiconnected(self):
+        self.assertTrue(self.g1.is_biconnected())
+        self.assertFalse(self.g2.is_biconnected())
+        self.assertFalse(self.g3.is_biconnected())
+        self.assertTrue(self.g4.is_biconnected())
+        self.assertFalse(self.g5.is_biconnected())
 
 
 class CentralityTests(unittest.TestCase):