Hi Mackx,
I quick note as I will comment deeper in another message.
In the apps "python" launchers in version 3a you write "import appcalc.py". That's not correct python, it should be "import appcalc", without the extension.
You use the syntax "import module.submodule" to import some submodules from a big package, as in "import books.epub", where you have a module books with different submodules:
Code:
python26/
lib/
site-packages/
books/
__init.py__
epub.py
pdf.py
...
Anyway, good work.