diff --git a/src/gsi/gsi/gsiClassBase.cc b/src/gsi/gsi/gsiClassBase.cc
index 0b609f590..f2b8baaa2 100644
--- a/src/gsi/gsi/gsiClassBase.cc
+++ b/src/gsi/gsi/gsiClassBase.cc
@@ -106,7 +106,9 @@ ClassBase::add_child_class (const ClassBase *cls)
   //  TODO: ugly const_cast hack
   ClassBase *non_const_cls = const_cast<ClassBase *> (cls);
   non_const_cls->set_parent (this);
-  m_child_classes.push_back (const_cast <ClassBase *> (cls));
+  //  child classes inherit the module of their parent
+  non_const_cls->set_module (module ());
+  m_child_classes.push_back (non_const_cls);
 }
 
 bool 
@@ -497,7 +499,6 @@ ClassBase::merge_declarations ()
     mp_class_collection->push_back (non_const_decl);
   }
   mp_new_class_collection->clear ();
-
 }
 
 void
diff --git a/src/pya/pya/pya.cc b/src/pya/pya/pya.cc
index 3da342664..625452425 100644
--- a/src/pya/pya/pya.cc
+++ b/src/pya/pya/pya.cc
@@ -58,25 +58,6 @@ class PYAObjectBase;
 
 // --------------------------------------------------------------------------
 
-#define PYA_TRY \
-  { \
-    try {
-
-#define PYA_CATCH(where) \
-    } catch (tl::ExitException &ex) { \
-      PyErr_SetObject (PyExc_SystemExit, c2python<int> (ex.status ())); \
-    } catch (std::exception &ex) { \
-      std::string msg = std::string(ex.what ()) + tl::to_string (QObject::tr (" in ")) + (where); \
-      PyErr_SetString (PyExc_RuntimeError, msg.c_str ()); \
-    } catch (tl::Exception &ex) { \
-      std::string msg = ex.msg () + tl::to_string (QObject::tr (" in ")) + (where); \
-      PyErr_SetString (PyExc_RuntimeError, msg.c_str ()); \
-    } catch (...) { \
-      std::string msg = tl::to_string (QObject::tr ("Unspecific exception in ")) + (where); \
-      PyErr_SetString (PyExc_RuntimeError, msg.c_str ()); \
-    } \
-  }
-
 /**
  *  @brief The python interpreter instance
  */
@@ -2265,6 +2246,18 @@ PythonModule::module ()
   return mp_module.get ();
 }
 
+PyObject *
+PythonModule::take_module ()
+{
+  return mp_module.release ();
+}
+
+void
+PythonModule::delete_module ()
+{
+  mp_module = PythonRef ();
+}
+
 void
 PythonModule::init (const char *mod_name, const char *description)
 {
@@ -2359,6 +2352,18 @@ PythonModule::make_classes (const char *mod_name)
 {
   PyObject *module = mp_module.get ();
 
+  //  Prepare an __all__ index for the module
+
+  PythonRef all_list;
+  if (! PyObject_HasAttrString (module, "__all__")) {
+    all_list = PythonRef (PyList_New (0));
+    PyObject_SetAttrString (module, "__all__", all_list.get ());
+  } else {
+    all_list = PythonRef (PyObject_GetAttrString (module, "__all__"));
+  }
+
+  PyObject_SetAttrString (module, "__doc__", PythonRef (c2python (m_mod_description)).get ());
+
   //  Create a (built-in) base class for all objects exposed by this module
 
   m_base_class_name = m_mod_name + ".__Base";
@@ -2421,6 +2426,9 @@ PythonModule::make_classes (const char *mod_name)
       for (tl::weak_collection<gsi::ClassBase>::const_iterator cc = c->begin_child_classes (); cc != c->end_child_classes (); ++cc) {
         tl_assert (cc->declaration () != 0);
         if (m_rev_cls_map.find (cc->declaration ()) == m_rev_cls_map.end ()) {
+          if (mod_name && cc->module () != mod_name) {
+            throw tl::Exception (tl::sprintf (tl::to_string (QObject::tr ("Class %s from module %s depends on %s.%s (try 'import klayout.%s' before 'import klayout.%s')")), c->name (), mod_name, cc->module (), cc->name (), cc->module (), mod_name));
+          }
           all_children_available = false;
           break;
         }
@@ -2432,6 +2440,9 @@ PythonModule::make_classes (const char *mod_name)
       }
 
       if (c->base () && m_rev_cls_map.find (c->base ()) == m_rev_cls_map.end ()) {
+        if (mod_name && c->base ()->module () != mod_name) {
+          throw tl::Exception (tl::sprintf (tl::to_string (QObject::tr ("Class %s from module %s depends on %s.%s (try 'import klayout.%s' before 'import klayout.%s')")), c->name (), mod_name, c->base ()->module (), c->base ()->name (), c->base ()->module (), mod_name));
+        }
         //  can't produce this class yet. The base class needs to be handled first.
         more_classes = true;
         continue;
@@ -2464,6 +2475,7 @@ PythonModule::make_classes (const char *mod_name)
       PyTypeObject *type = (PyTypeObject *) PyObject_Call ((PyObject *) &PyType_Type, args.get (), NULL);
       tl_assert (type != NULL);
 
+      PyList_Append (all_list.get (), PythonRef (c2python (c->name ())).get ());
       PyModule_AddObject (module, c->name ().c_str (), (PyObject *) type);
 
       m_cls_map.insert (std::make_pair (type, &*c));
diff --git a/src/pya/pya/pya.h b/src/pya/pya/pya.h
index 2561c3339..d429d933b 100644
--- a/src/pya/pya/pya.h
+++ b/src/pya/pya/pya.h
@@ -68,6 +68,42 @@ namespace pya
     throw; \
   } 
 
+/**
+ *  Two helper macros that translate C++ exceptions into Python errors
+ */
+
+#define PYA_TRY \
+  { \
+    try {
+
+#define PYA_CATCH(where) \
+    } catch (tl::ExitException &ex) { \
+      PyErr_SetObject (PyExc_SystemExit, PyLong_FromLong (ex.status ())); \
+    } catch (std::exception &ex) { \
+      std::string msg = std::string(ex.what ()) + tl::to_string (QObject::tr (" in ")) + (where); \
+      PyErr_SetString (PyExc_RuntimeError, msg.c_str ()); \
+    } catch (tl::Exception &ex) { \
+      std::string msg; \
+      msg = ex.msg () + tl::to_string (QObject::tr (" in ")) + (where); \
+      PyErr_SetString (PyExc_RuntimeError, msg.c_str ()); \
+    } catch (...) { \
+      std::string msg = tl::to_string (QObject::tr ("Unspecific exception in ")) + (where); \
+      PyErr_SetString (PyExc_RuntimeError, msg.c_str ()); \
+    } \
+  }
+
+#define PYA_CATCH_ANYWHERE \
+    } catch (tl::ExitException &ex) { \
+      PyErr_SetObject (PyExc_SystemExit, PyLong_FromLong (ex.status ())); \
+    } catch (std::exception &ex) { \
+      PyErr_SetString (PyExc_RuntimeError, ex.what ()); \
+    } catch (tl::Exception &ex) { \
+      PyErr_SetString (PyExc_RuntimeError, ex.msg ().c_str ()); \
+    } catch (...) { \
+      PyErr_SetString (PyExc_RuntimeError, tl::to_string (QObject::tr ("Unspecific exception in ")).c_str ()); \
+    } \
+  }
+
 /**
  *  @brief A class encapsulating a python exception
  */
@@ -143,10 +179,21 @@ public:
   static std::string python_doc (const gsi::MethodBase *method);
 
   /**
-   *  @brief Gets the PyObject for the module
+   *  @brief Gets the PyModule object
    */
   PyObject *module ();
 
+  /**
+   *  @brief Gets the PyModule object
+   *  This method will release the ownership over the PyObject
+   */
+  PyObject *take_module ();
+
+  /**
+   *  @brief Deletes the PyModule object
+   */
+  void delete_module ();
+
 private:
   void add_python_doc (const gsi::ClassBase &cls, const MethodTable *mt, int mid, const std::string &doc);
   PyMethodDef *make_method_def ();
diff --git a/src/pymod/QtCore/QtCore.pro b/src/pymod/QtCore/QtCore.pro
new file mode 100644
index 000000000..7d2ba4efc
--- /dev/null
+++ b/src/pymod/QtCore/QtCore.pro
@@ -0,0 +1,21 @@
+
+LIBDIR = $$OUT_PWD/../..
+DESTDIR = $$LIBDIR/pymod
+TARGET = QtCore
+
+include($$PWD/../../lib.pri)
+
+SOURCES = \
+  QtCoreMain.cc \
+
+HEADERS += \
+
+INCLUDEPATH += $$PYTHONINCLUDE $$TL_INC $$GSI_INC $$PYA_INC
+DEPENDPATH += $$PYTHONINCLUDE $$TL_INC $$GSI_INC $$PYA_INC
+LIBS += $$PYTHONLIBFILE -L$$LIBDIR -lklayout_tl -lklayout_db -lklayout_gsi -lklayout_pya -lklayout_QtCore
+
+# Python is somewhat sloppy and relies on the compiler initializing fields 
+# of strucs to 0:
+QMAKE_CXXFLAGS_WARN_ON += \
+    -Wno-missing-field-initializers
+
diff --git a/src/pymod/QtCore/QtCoreMain.cc b/src/pymod/QtCore/QtCoreMain.cc
new file mode 100644
index 000000000..a325ad7db
--- /dev/null
+++ b/src/pymod/QtCore/QtCoreMain.cc
@@ -0,0 +1,25 @@
+
+/*
+
+  KLayout Layout Viewer
+  Copyright (C) 2006-2018 Matthias Koefferlein
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+*/
+
+#include "../pymodHelper.h"
+
+DEFINE_PYMOD(QtCore, "QtCore", "KLayout/Qt module 'QtCore'")
diff --git a/src/pymod/QtGui/QtGui.pro b/src/pymod/QtGui/QtGui.pro
new file mode 100644
index 000000000..681523ceb
--- /dev/null
+++ b/src/pymod/QtGui/QtGui.pro
@@ -0,0 +1,21 @@
+
+LIBDIR = $$OUT_PWD/../..
+DESTDIR = $$LIBDIR/pymod
+TARGET = QtGui
+
+include($$PWD/../../lib.pri)
+
+SOURCES = \
+  QtGuiMain.cc \
+
+HEADERS += \
+
+INCLUDEPATH += $$PYTHONINCLUDE $$TL_INC $$GSI_INC $$PYA_INC
+DEPENDPATH += $$PYTHONINCLUDE $$TL_INC $$GSI_INC $$PYA_INC
+LIBS += $$PYTHONLIBFILE -L$$LIBDIR -lklayout_tl -lklayout_db -lklayout_gsi -lklayout_pya -lklayout_QtGui -lklayout_QtCore
+
+# Python is somewhat sloppy and relies on the compiler initializing fields 
+# of strucs to 0:
+QMAKE_CXXFLAGS_WARN_ON += \
+    -Wno-missing-field-initializers
+
diff --git a/src/pymod/QtGui/QtGuiMain.cc b/src/pymod/QtGui/QtGuiMain.cc
new file mode 100644
index 000000000..43b77f742
--- /dev/null
+++ b/src/pymod/QtGui/QtGuiMain.cc
@@ -0,0 +1,25 @@
+
+/*
+
+  KLayout Layout Viewer
+  Copyright (C) 2006-2018 Matthias Koefferlein
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+*/
+
+#include "../pymodHelper.h"
+
+DEFINE_PYMOD(QtGui, "QtGui", "KLayout/Qt module 'QtGui'")
diff --git a/src/pymod/db/dbMain.cc b/src/pymod/db/dbMain.cc
index a63d96da1..a0886149d 100644
--- a/src/pymod/db/dbMain.cc
+++ b/src/pymod/db/dbMain.cc
@@ -20,37 +20,6 @@
 
 */
 
-#include <Python.h>
-#include "pya.h"
-#include "gsi.h"
-#include "gsiExpression.h"
+#include "../pymodHelper.h"
 
-static PyObject *module_init ()
-{
-  gsi::initialize ();
-
-  //  required for the tiling processor for example
-  gsi::initialize_expressions ();
-
-  static pya::PythonModule module;
-  module.init ("klayout.db", "KLayout core module (db)");
-  module.make_classes ("db");
-
-  return module.module ();
-}
-
-#if PY_MAJOR_VERSION < 3
-PyMODINIT_FUNC
-DEF_INSIDE_PUBLIC
-initdb ()
-{
-  module_init ();
-}
-#else
-PyMODINIT_FUNC
-DEF_INSIDE_PUBLIC
-PyInit_db ()
-{
-  return module_init();
-}
-#endif
+DEFINE_PYMOD(db, "db", "KLayout core module 'db'")
diff --git a/src/pymod/lay/layMain.cc b/src/pymod/lay/layMain.cc
index 4e313ee11..30b945094 100644
--- a/src/pymod/lay/layMain.cc
+++ b/src/pymod/lay/layMain.cc
@@ -20,37 +20,6 @@
 
 */
 
-#include <Python.h>
-#include "pya.h"
-#include "gsi.h"
-#include "gsiExpression.h"
+#include "../pymodHelper.h"
 
-static PyObject *module_init ()
-{
-  gsi::initialize ();
-
-  //  required for the tiling processor for example
-  gsi::initialize_expressions ();
-
-  static pya::PythonModule module;
-  module.init ("klayout.lay", "KLayout core module (lay)");
-  module.make_classes ("lay");
-
-  return module.module ();
-}
-
-#if PY_MAJOR_VERSION < 3
-PyMODINIT_FUNC
-DEF_INSIDE_PUBLIC
-initlay ()
-{
-  module_init ();
-}
-#else
-PyMODINIT_FUNC
-DEF_INSIDE_PUBLIC
-PyInit_lay ()
-{
-  return module_init();
-}
-#endif
+DEFINE_PYMOD(lay, "lay", "KLayout core module 'lay'")
diff --git a/src/pymod/pymod.pro b/src/pymod/pymod.pro
index a5c87b566..28ab71b6b 100644
--- a/src/pymod/pymod.pro
+++ b/src/pymod/pymod.pro
@@ -4,4 +4,6 @@ SUBDIRS = \
   db \
   tl \
   lay \
+  QtGui \
+  QtCore \
 
diff --git a/src/pymod/pymodHelper.h b/src/pymod/pymodHelper.h
new file mode 100644
index 000000000..034b8efdf
--- /dev/null
+++ b/src/pymod/pymodHelper.h
@@ -0,0 +1,84 @@
+
+
+/*
+
+  KLayout Layout Viewer
+  Copyright (C) 2006-2018 Matthias Koefferlein
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+*/
+
+/**
+ *  @brief A helper include file to implement the Python modules
+ *
+ *  Use this helper file this way:
+ *
+ *  #include "pymodHelper.h"
+ *  DEFINE_PYMOD(mymod, "mymod", "KLayout Test module klayout.mymod")
+ */
+
+#include <Python.h>
+#include "pya.h"
+#include "gsi.h"
+#include "gsiExpression.h"
+
+static PyObject *
+module_init (const char *mod_name, const char *mod_description)
+{
+  static pya::PythonModule module;
+  std::string mod_qname (std::string ("klayout.") + mod_name);
+  std::string import_text ("'import " + mod_qname + "'");
+  
+  PYA_TRY
+  
+    gsi::initialize ();
+
+    //  required for the tiling processor for example
+    gsi::initialize_expressions ();
+
+    module.init (mod_qname.c_str (), mod_description);
+    module.make_classes (mod_name);
+
+    return module.take_module ();
+
+  PYA_CATCH_ANYWHERE
+  
+  module.delete_module ();
+  return 0;
+}
+
+#if PY_MAJOR_VERSION < 3
+
+#define DEFINE_PYMOD(__name__, __name_str__, __description__) \
+  PyMODINIT_FUNC \
+  DEF_INSIDE_PUBLIC \
+  init##__name__ () \
+  { \
+    module_init (__name_str__, __description__); \
+  } \
+
+#else
+
+#define DEFINE_PYMOD(__name__, __name_str__, __description__) \
+  PyMODINIT_FUNC \
+  DEF_INSIDE_PUBLIC \
+  PyInit_##__name__ () \
+  { \
+    return module_init (__name_str__, __description__); \
+  } \
+
+#endif
+
diff --git a/src/pymod/tl/tlMain.cc b/src/pymod/tl/tlMain.cc
index 46b1666fa..db6a278fb 100644
--- a/src/pymod/tl/tlMain.cc
+++ b/src/pymod/tl/tlMain.cc
@@ -20,37 +20,6 @@
 
 */
 
-#include <Python.h>
-#include "pya.h"
-#include "gsi.h"
-#include "gsiExpression.h"
+#include "../pymodHelper.h"
 
-static PyObject *module_init ()
-{
-  gsi::initialize ();
-
-  //  required for the tiling processor for example
-  gsi::initialize_expressions ();
-
-  static pya::PythonModule module;
-  module.init ("klayout.tl", "KLayout core module (tl)");
-  module.make_classes ("tl");
-
-  return module.module ();
-}
-
-#if PY_MAJOR_VERSION < 3
-PyMODINIT_FUNC
-DEF_INSIDE_PUBLIC
-inittl ()
-{
-  module_init ();
-}
-#else
-PyMODINIT_FUNC
-DEF_INSIDE_PUBLIC
-PyInit_tl ()
-{
-  return module_init();
-}
-#endif
+DEFINE_PYMOD(tl, "tl", "KLayout core module 'tl'")