RAII wrapper for error state

include/pybind11/cast.h

@@ -111,18 +111,16 @@ PYBIND11_NOINLINE inline std::string error_string() {
         return "Unknown internal error occurred";
     }
 
-    PyObject *type, *value, *traceback;
-    PyErr_Fetch(&type, &value, &traceback);
+    error_scope scope; // Preserve error state
 
     std::string errorString;
-    if (type) {
-        errorString += handle(type).attr("__name__").cast<std::string>();
+    if (scope.type) {
+        errorString += handle(scope.type).attr("__name__").cast<std::string>();
         errorString += ": ";
     }
-    if (value)
-        errorString += (std::string) handle(value).str();
+    if (scope.value)
+        errorString += (std::string) handle(scope.value).str();
 
-    PyErr_Restore(type, value, traceback);
     return errorString;
 }
 

include/pybind11/common.h

@@ -420,6 +420,13 @@ template <typename T> struct format_descriptor<T, typename std::enable_if<std::i
 template <typename T> constexpr const char format_descriptor<
     T, typename std::enable_if<std::is_integral<T>::value>::type>::value[2];
 
+/// RAII wrapper that temporarily clears any Python error state
+struct error_scope {
+    PyObject *type, *value, *trace;
+    error_scope() { PyErr_Fetch(&type, &value, &trace); }
+    ~error_scope() { PyErr_Restore(type, value, trace); }
+};
+
 PYBIND11_DECL_FMT(float, "f");
 PYBIND11_DECL_FMT(double, "d");
 PYBIND11_DECL_FMT(bool, "?");

include/pybind11/pybind11.h

@@ -1309,6 +1309,7 @@ NAMESPACE_END(detail)
 
 template <return_value_policy policy = return_value_policy::automatic_reference, typename... Args>
 void print(Args &&...args) {
+    error_scope scope; // Preserve error state
     auto c = detail::collect_arguments<policy>(std::forward<Args>(args)...);
     detail::print(c.args(), c.kwargs());
 }