fix: support exact integers as floats for IntCat

Author: henryiii

include/bh_python/register_axis.hpp

@@ -47,6 +47,27 @@ auto vectorize_index(T input) {
 #define BHP_NOEXCEPT_17
 #endif
 
+namespace detail {
+template <class T>
+decltype(auto) axis_cast(py::handle x) {
+    return special_cast<T>(x);
+}
+
+template <>
+inline decltype(auto) axis_cast<int>(py::handle x) {
+    if(py::isinstance<int>(x))
+        return py::cast<int>(x);
+
+    auto val  = py::cast<float>(x);
+    auto ival = static_cast<int>(val);
+
+    if(static_cast<float>(ival) == val)
+        return ival;
+
+    throw py::type_error(py::str("cannot cast {} to int").format(val));
+}
+} // namespace detail
+
 // we overload vectorize index for category axis
 template <class T, class Options>
 auto vectorize_index(int (bh::axis::category<T, metadata_t, Options>::*pindex)(const T&)
@@ -56,7 +77,7 @@ auto vectorize_index(int (bh::axis::category<T, metadata_t, Options>::*pindex)(c
         auto index = std::mem_fn(pindex);
 
         if(detail::is_value<T>(arg)) {
-            auto index_value = index(self, detail::special_cast<T>(arg));
+            auto index_value = index(self, detail::axis_cast<T>(arg));
             if(index_value >= self.size())
                 throw pybind11::key_error(py::str("{!r} not in axis").format(arg));
             return py::cast(index_value);