code review: boundaries uses only once find and return a pair of iterator. Exception is raised when not found. tested

4 files changed, 23 insertions, 15 deletions

diff --git a/src/python/gudhi/simplex_tree.pxd b/src/python/gudhi/simplex_tree.pxd
index a64599e7..e1b03391 100644
--- a/src/python/gudhi/simplex_tree.pxd
+++ b/src/python/gudhi/simplex_tree.pxd
@@ -71,8 +71,7 @@ cdef extern from "Simplex_tree_interface.h" namespace "Gudhi":
         vector[Simplex_tree_simplex_handle].const_iterator get_filtration_iterator_end() nogil
         Simplex_tree_skeleton_iterator get_skeleton_iterator_begin(int dimension) nogil
         Simplex_tree_skeleton_iterator get_skeleton_iterator_end(int dimension) nogil
-        Simplex_tree_boundary_iterator get_boundary_iterator_begin(vector[int] simplex) nogil
-        Simplex_tree_boundary_iterator get_boundary_iterator_end(vector[int] simplex) nogil
+        pair[Simplex_tree_boundary_iterator, Simplex_tree_boundary_iterator] get_boundary_iterators(vector[int] simplex) nogil except +
 
 cdef extern from "Persistent_cohomology_interface.h" namespace "Gudhi":
     cdef cppclass Simplex_tree_persistence_interface "Gudhi::Persistent_cohomology_interface<Gudhi::Simplex_tree<Gudhi::Simplex_tree_options_full_featured>>":
diff --git a/src/python/gudhi/simplex_tree.pyx b/src/python/gudhi/simplex_tree.pyx
index 3ebae923..bc5b43f4 100644
--- a/src/python/gudhi/simplex_tree.pyx
+++ b/src/python/gudhi/simplex_tree.pyx
@@ -293,12 +293,14 @@ cdef class SimplexTree:
         :returns:  The (simplices of the) boundary of a simplex
         :rtype:  generator with tuples(simplex, filtration)
         """
-        cdef Simplex_tree_boundary_iterator it =  self.get_ptr().get_boundary_iterator_begin(simplex)
-        cdef Simplex_tree_boundary_iterator end = self.get_ptr().get_boundary_iterator_end(simplex)
-
-        while it != end:
-            yield self.get_ptr().get_simplex_and_filtration(dereference(it))
-            preincrement(it)
+        cdef pair[Simplex_tree_boundary_iterator, Simplex_tree_boundary_iterator] it =  self.get_ptr().get_boundary_iterators(simplex)
+
+        try:
+            while it.first != it.second:
+                yield self.get_ptr().get_simplex_and_filtration(dereference(it.first))
+                preincrement(it.first)
+        except RuntimeError:
+            print("simplex not found - cannot find boundaries")
 
 
     def remove_maximal_simplex(self, simplex):
diff --git a/src/python/include/Simplex_tree_interface.h b/src/python/include/Simplex_tree_interface.h
index c4f18eeb..2c695d1b 100644
--- a/src/python/include/Simplex_tree_interface.h
+++ b/src/python/include/Simplex_tree_interface.h
@@ -190,14 +190,12 @@ class Simplex_tree_interface : public Simplex_tree<SimplexTreeOptions> {
     return Base::skeleton_simplex_range(dimension).end();
   }
 
-  Boundary_simplex_iterator get_boundary_iterator_begin(const Simplex& simplex) {
+  std::pair<Boundary_simplex_iterator, Boundary_simplex_iterator> get_boundary_iterators(const Simplex& simplex) {
+    auto bd_sh = Base::find(simplex);
+    if (bd_sh == Base::null_simplex())
+      throw std::runtime_error("simplex not found - cannot find boundaries");
     // this specific case works because the range is just a pair of iterators - won't work if range was a vector
-    return Base::boundary_simplex_range(Base::find(simplex)).begin();
-  }
-
-  Boundary_simplex_iterator get_boundary_iterator_end(const Simplex& simplex) {
-    // this specific case works because the range is just a pair of iterators - won't work if range was a vector
-    return Base::boundary_simplex_range(Base::find(simplex)).end();
+    return std::make_pair(Base::boundary_simplex_range(bd_sh).begin(), Base::boundary_simplex_range(bd_sh).end());
   }
 };
 
diff --git a/src/python/test/test_simplex_tree.py b/src/python/test/test_simplex_tree.py
index 036e88df..828400fb 100755
--- a/src/python/test/test_simplex_tree.py
+++ b/src/python/test/test_simplex_tree.py
@@ -350,3 +350,12 @@ def test_boundaries_iterator():
     assert list(st.get_boundaries([1, 2, 3])) == [([1, 2], 1.0), ([1, 3], 1.0), ([2, 3], 1.0)]
     assert list(st.get_boundaries([2, 3, 4])) == [([2, 3], 1.0), ([2, 4], 2.0), ([3, 4], 2.0)]
     assert list(st.get_boundaries([2])) == []
+
+    with pytest.raises(RuntimeError):
+        list(st.get_boundaries([]))
+
+    with pytest.raises(RuntimeError):
+        list(st.get_boundaries([0, 4])) # (0, 4) does not exist
+
+    with pytest.raises(RuntimeError):
+        list(st.get_boundaries([6])) # (6) does not exist