Clear python variables in script window when executing whole script

Refs #9270

Code/Mantid/MantidPlot/src/PythonScript.cpp

@@ -417,6 +417,19 @@ void PythonScript::setContext(QObject *context)
   setQObject(context, "self");
 }
 
+/**
+ * Clears the current set of local variables and resets
+ * the dictionary context back to the default set
+ */
+void PythonScript::clearLocals()
+{
+  GlobalInterpreterLock pythonlock;
+
+  Py_XDECREF(localDict); //clear up any previous dictionary
+  PyObject *pymodule = PyImport_AddModule("__main__");
+  localDict = PyDict_Copy(PyModule_GetDict(pymodule));
+}
+
 /**
  * Sets the context for the script and if name points to a file then
  * sets the __file__ variable
@@ -425,9 +438,9 @@ void PythonScript::setContext(QObject *context)
  */
 void PythonScript::initialize(const QString & name, QObject *context)
 {
+  clearLocals(); // holds and releases GIL
+
   GlobalInterpreterLock pythonlock;
-  PyObject *pymodule = PyImport_AddModule("__main__");
-  localDict = PyDict_Copy(PyModule_GetDict(pymodule));
   PythonScript::setIdentifier(name);
   setContext(context);
 }

Code/Mantid/MantidPlot/src/PythonScript.h

@@ -93,6 +93,8 @@ class PythonScript : public Script, MantidQt::API::WorkspaceObserver
   bool setDouble(double val, const char* name);
   /// Set the context for this script
   void setContext(QObject *context);
+  /// Resets the local dictionary to the defaults
+  void clearLocals();
 
 private:
   /// Helper class to ensure the sys.path variable is updated correctly

Code/Mantid/MantidPlot/src/Script.h

@@ -118,6 +118,7 @@ public slots:
   virtual bool setQObject(QObject*, const char*) { return false; }
   virtual bool setInt(int, const char*) { return false; }
   virtual bool setDouble(double, const char*) { return false; }
+  virtual void clearLocals() {}
 
 signals:
   /// A signal defining when this script has started executing

Code/Mantid/MantidPlot/src/ScriptFileInterpreter.cpp

@@ -225,10 +225,12 @@ void ScriptFileInterpreter::showFindReplaceDialog()
 }
 
 /**
- * Execute the whole script in the editor.
+ * Execute the whole script in the editor. Always clears the contents of the
+ * local variable dictionary first.
  */
 void ScriptFileInterpreter::executeAll(const Script::ExecutionMode mode)
 {
+  m_runner->clearLocals();
   executeCode(m_editor->text(), mode);
 }