all tests pass

src/python/axis.cpp

@@ -146,7 +146,7 @@ bp::str axis_get_label(const T& t) {
 
 template <typename A>
 bp::object axis_getitem(const A& a, int i) {
-  if (i < -1 * a.uoflow() || i >= a.size() + 1 * a.uoflow())
+  if (i < -(a.uoflow() == 2) || i >= (a.size() + int(a.uoflow() > 0)))
     throw std::out_of_range("index out of bounds");
   return bp::make_tuple(a.lower(i), a.lower(i + 1));
 }

src/python/histogram.cpp

@@ -316,9 +316,6 @@ bp::object histogram_reduce_to(bp::tuple args, bp::dict kwargs) {
 
   const auto nargs = bp::len(args) - 1;
   if (nargs == 0) { throw std::invalid_argument("at least one argument required"); }
-  if (nargs < self.dim()) {
-    throw std::invalid_argument("fewer arguments than histogram axes required");
-  }
 
   if (nargs > BOOST_HISTOGRAM_AXIS_LIMIT) {
     throw std::invalid_argument(
@@ -327,7 +324,11 @@ bp::object histogram_reduce_to(bp::tuple args, bp::dict kwargs) {
   }
 
   int idx[BOOST_HISTOGRAM_AXIS_LIMIT];
-  for (auto i = 0u; i < nargs; ++i) idx[i] = bp::extract<int>(args[1 + i]);
+  for (auto i = 0u; i < nargs; ++i) {
+    idx[i] = bp::extract<int>(args[1 + i]);
+    if (i > 0 && idx[i] <= idx[i - 1])
+      throw std::invalid_argument("indices must be strictly ascending");
+  }
 
   return bp::object(self.reduce_to(idx, idx + nargs));
 }

src/python/module.cpp

@@ -7,6 +7,7 @@
 #include <boost/python/module.hpp>
 #include <boost/python/object.hpp>
 #include <boost/python/scope.hpp>
+#include <stdexcept>
 #ifdef HAVE_NUMPY
 #include <boost/python/numpy.hpp>
 #endif
@@ -16,6 +17,10 @@ void register_histogram();
 
 BOOST_PYTHON_MODULE(histogram) {
   using namespace boost::python;
+
+  register_exception_translator<std::out_of_range>(
+      [](const std::out_of_range& e) { PyErr_SetString(PyExc_IndexError, e.what()); });
+
   scope current;
 #ifdef HAVE_NUMPY
   numpy::initialize();