Can I make a module out of a worksheet?

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I have been using save_session and load_session to re-use symbolic expressions and dictionaries across worksheets, but I still need to re-type all sorts of python functions (e.g. def fun()...), which cannot be pickled. Now I am wondering whether there is a way to automatically create a .py file out of a worksheet, i.e. a module that contains all code from a worksheet, excluding html comments. This could then be loaded as a module in other worksheets, allowing also to keep the namespaces separate, which would be awesome. Does anyone know of a script/method to do this?