don't use deprecated parser module

Python interpreter in DNG uses the parser module to identify simple
one line expressions. That module is gone in Python 3.10.
Functionality gets replaced by the builtin compile function.

modules/gui/src/python_shell/python_interpreter_worker.cc

@@ -21,6 +21,7 @@
 #include "python_interpreter_worker.hh"
 #include "python_interpreter.hh"
 
+
 namespace ost { namespace gui {
 
     namespace {
@@ -55,7 +56,7 @@ PythonInterpreterWorker::PythonInterpreterWorker():
   current_id_(),
   awake_(false)
 {
-  parse_expr_cmd_=bp::import("parser").attr("expr");
+  parse_expr_cmd_=bp::import("__main__").attr("__builtins__").attr("compile");
   main_namespace_ = bp::extract<bp::dict>(bp::import("__main__").attr("__dict__"));
   repr_=bp::import("__main__").attr("__builtins__").attr("repr");
   #ifndef _MSC_VER
@@ -98,16 +99,6 @@ unsigned int PythonInterpreterWorker::AddCommand(const QString& command)
   return command_id_;
 }
 
-bool PythonInterpreterWorker::is_simple_expression_(const QString& expr)
-{
-  try {
-    parse_expr_cmd_(bp::str(expr.toStdString()));
-    return true;
-  } catch(bp::error_already_set&) {
-    PyErr_Clear();
-    return false;
-  }
-}
 void PythonInterpreterWorker::run_command_(std::pair<unsigned int,QString> pair)
 {
   #ifndef _MSC_VER
@@ -148,7 +139,7 @@ void PythonInterpreterWorker::run_command_(std::pair<unsigned int,QString> pair)
 bool PythonInterpreterWorker::is_simple_expression(const QString& expr)
 {
   try {
-    parse_expr_cmd_(bp::str(expr.toStdString()));
+    parse_expr_cmd_(bp::str(expr.toStdString()), "<string>", "eval");
     return true;
   } catch(bp::error_already_set&) {
     PyErr_Clear();

modules/gui/src/python_shell/python_interpreter_worker.hh

@@ -62,7 +62,6 @@ protected slots:
 protected:
   bool is_simple_expression(const QString& expr);
   void run_command_(std::pair<unsigned int,QString> pair);
-  bool is_simple_expression_(const QString& expr);
   QQueue<std::pair<unsigned int,QString> > exec_queue_;
   unsigned int command_id_;
   boost::shared_ptr<OutputRedirector>  output_redirector_;