diff --git a/src/python/histogram.cpp b/src/python/histogram.cpp
index 57b0589f..34c66824 100644
--- a/src/python/histogram.cpp
+++ b/src/python/histogram.cpp
@@ -38,6 +38,11 @@ struct axis_visitor : public static_visitor<python::object>
 python::object
 histogram_axis(const dynamic_histogram<>& self, unsigned i)
 {
+  if (i < 0) i += self.dim();
+  if (i < 0 || i >= self.dim()) {
+    PyErr_SetString(PyExc_IndexError, "axis index out of range");
+    python::throw_error_already_set();
+  }
   return apply_visitor(axis_visitor(), self.axis(i));
 }
 
@@ -275,6 +280,13 @@ struct storage_access {
       return python::object();
     }
 
+    if (!b.ptr_) {
+      // PyErr_SetString(PyExc_KeyError, "cannot convert empty histogram");
+      // python::throw_error_already_set();
+      // workaround: for some reason, exception is ignored here
+      return python::object();
+    }
+
     python::dict d;
     python::list shapes;
     python::list strides;
@@ -318,8 +330,8 @@ void register_histogram()
     .def(init<const dynamic_histogram<>&>())
     .add_property("__array_interface__",
         &storage_access::array_interface)
-    .add_property("dim", &dynamic_histogram<>::dim,
-       "dimensions of the histogram (number of axes)")
+    .def("__len__", &dynamic_histogram<>::dim)
+    .def("__getitem__", histogram_axis)
     .def("axis", histogram_axis,
        ":param int i: index of the axis\n"
        ":returns: axis object for axis i",
diff --git a/test/python_suite_test.py.in b/test/python_suite_test.py.in
index 956db150..80cd37bd 100755
--- a/test/python_suite_test.py.in
+++ b/test/python_suite_test.py.in
@@ -327,7 +327,7 @@ class histogramtest(unittest.TestCase):
             histogram(integer_axis(-1, 1), unknown_keyword="nh")
 
         h = histogram(integer_axis(-1, 1))
-        self.assertEqual(h.dim, 1)
+        self.assertEqual(len(h), 1)
         self.assertEqual(h.axis(0), integer_axis(-1, 1))
         self.assertEqual(h.axis(0).shape, 5)
         self.assertEqual(histogram(integer_axis(-1, 1, uoflow=False)).axis(0).shape, 3)
@@ -522,7 +522,7 @@ class histogramtest(unittest.TestCase):
         io.seek(0)
         b = pickle.load(io)
         self.assertNotEqual(id(a), id(b))
-        self.assertEqual(a.dim, b.dim)
+        self.assertEqual(len(a), len(b))
         self.assertEqual(a.axis(0), b.axis(0))
         self.assertEqual(a.axis(1), b.axis(1))
         self.assertEqual(a.axis(2), b.axis(2))
@@ -550,7 +550,7 @@ class histogramtest(unittest.TestCase):
         io.seek(0)
         b = pickle.load(io)
         self.assertNotEqual(id(a), id(b))
-        self.assertEqual(a.dim, b.dim)
+        self.assertEqual(len(a), len(b))
         self.assertEqual(a.axis(0), b.axis(0))
         self.assertEqual(a.axis(1), b.axis(1))
         self.assertEqual(a.axis(2), b.axis(2))