From 720136bfa7bba696feb2e56a24a34ff09b9322c3 Mon Sep 17 00:00:00 2001
From: Wenzel Jakob <wenzel.jakob@epfl.ch>
Date: Sat, 10 Sep 2016 16:32:17 +0900
Subject: [PATCH] RAII wrapper for error state

---
 include/pybind11/cast.h     | 12 +++++-------
 include/pybind11/common.h   |  7 +++++++
 include/pybind11/pybind11.h |  1 +
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index fae8d89cf..638e4245f 100644
--- a/include/pybind11/cast.h
+++ b/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;
 }
 
diff --git a/include/pybind11/common.h b/include/pybind11/common.h
index 255cc79a3..ef92daff7 100644
--- a/include/pybind11/common.h
+++ b/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, "?");
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index d3be7e214..4a50b3353 100644
--- a/include/pybind11/pybind11.h
+++ b/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());
 }