python: Add std::vector<std::string> support (Fix #2453)

ortools/base/python-swig.h

@@ -218,6 +218,14 @@ inline int SwigPyIntOrLong_Check(PyObject* o) {
   );  // NOLINT
 }
 
+inline int SwigString_Check(PyObject* o) {
+#if PY_VERSION_HEX >= 0x03030000
+  return PyUnicode_Check(o);
+#else
+  return true;
+#endif
+}
+
 inline PyObject* SwigString_FromString(const std::string& s) {
   return PyString_FromStringAndSize(s.data(), s.size());
 }

ortools/util/python/vector.i

@@ -86,6 +86,7 @@
 PY_LIST_INPUT_OUTPUT_TYPEMAP(int, PyInt_Check, PyInt_FromLong);
 PY_LIST_INPUT_OUTPUT_TYPEMAP(int64, SwigPyIntOrLong_Check, PyLong_FromLongLong);
 PY_LIST_INPUT_OUTPUT_TYPEMAP(double, PyFloat_Check, PyFloat_FromDouble);
+PY_LIST_INPUT_OUTPUT_TYPEMAP(std::string, SwigString_Check, SwigString_FromString);
 
 // Add conversion list(tuple(int)) -> std::vector<std::vector>.
 // TODO(user): see if we can also get rid of this and utilize already