Fix typemap for str/bytes -> std::string

wrappers/python/src/swig_doxygen/swig_lib/python/typemaps.i

@@ -169,11 +169,10 @@
     $result = PyBytes_FromStringAndSize($1.c_str(), $1.length());
 }
 
-
-%typemap(in) std::string {
-    // if we have a C++ method that takes in a std::string, we're most happy to accept
-    // a python bytes object. But if the user passes in a unicode object we'll try
-    // to recover by encoding it to UTF-8 bytes
+%typemap(in) const std::string & {
+    // if we have a C++ method that takes in a std::string, we're most happy to
+    // accept a python bytes object. But if the user passes in a unicode object
+    // we'll try to recover by encoding it to UTF-8 bytes
     PyObject* temp = NULL;
     char* c_str = NULL;
     Py_ssize_t len = 0;
@@ -181,19 +180,24 @@
     if (PyUnicode_Check($input)) {
         temp = PyUnicode_AsUTF8String($input);
         if (temp == NULL) {
-            SWIG_exception_fail(SWIG_TypeError, "'utf-8' codec can't decode byte");
+            SWIG_exception_fail(SWIG_TypeError, "$symname: 'utf-8' codec can't decode byte");
         }
         PyBytes_AsStringAndSize(temp, &c_str, &len);
         Py_XDECREF(temp);
     } else if (PyBytes_Check($input)) {
         PyBytes_AsStringAndSize($input, &c_str, &len);
     } else {
-         SWIG_exception_fail(SWIG_TypeError, "argument must be str or bytes");
+        SWIG_exception_fail(SWIG_TypeError, "$symname: argument must be str or bytes");
     }
 
     if (c_str == NULL) {
-        SWIG_exception_fail(SWIG_TypeError, "argument must be str or bytes");
+        SWIG_exception_fail(SWIG_TypeError, "$symname: argument must be str or bytes");
     }
 
-    $1 = std::string(c_str, len);
+    std::string temp2(c_str, len);
+    $1 = &temp2;
+}
+
+%typemap(freearg) const std::string & {
+    // Don't delete me
 }