From f1435c7e6b068a1ed13ebd3db597ea3bb15aa398 Mon Sep 17 00:00:00 2001
From: Sergei Lebedev <slebedev@google.com>
Date: Wed, 28 Aug 2019 17:52:41 +0100
Subject: [PATCH] Extract exception name via tp_name
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This is faster than dynamically looking up __name__ via GetAttrString.
Note though that the runtime of the code throwing an error_already_set
will be dominated by stack unwinding so the improvement will not be
noticeable.

Before:

396 ns ± 0.913 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

After:

277 ns ± 0.549 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

Benchmark:

const std::string foo() {
    PyErr_SetString(PyExc_KeyError, "");
    const std::string &s = py::detail::error_string();
    PyErr_Clear();
    return s;
}

PYBIND11_MODULE(foo, m) {
    m.def("foo", &::foo);
}
---
 include/pybind11/cast.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 8bcf81761..c02708195 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -413,7 +413,7 @@ PYBIND11_NOINLINE inline std::string error_string(PyObject* type, PyObject* valu
     // normalized by the caller?
     std::string errorString;
     if (type) {
-        errorString += handle(type).attr("__name__").cast<std::string>();
+        errorString += static_cast<const std::string>(reinterpret_cast<PyTypeObject*>(type)->tp_name);
         errorString += ": ";
     }
     if (value)