Error on python shelve when saving an empty list

Question

I want to save all of my variables (including primitives, objects, lists, dictionaries, etc.) with python shelve. In my workspace, I have a few empty lists which will be used and filled on specific conditions or on the next steps of my code. Unfortunately, when I want to save my workspace with python shelve it raises an error on empty list keys. My code is as below:

for key in dir():   
    try:
        my_ws[key] = globals()[key]
    except TypeError:       
        print('ERROR shelving: {0}'.format(key))

Do you have any idea?

Answer 1

Shelve doesn't have problem with empty lists.

Please make sure: 1) you initialize the shelve object properly before using it. 2) exclude all elements that shelve cannot serialize. It uses pickle module and all elements supported may be found here:
https://docs.python.org/3/library/pickle.html#what-can-be-pickled-and-unpickled

Check if below code will work for you and if you get any errors.

import inspect
import shelve
my_ws = shelve.open('test')
for key in dir():
    if not inspect.ismodule(globals()[key]):
        try:
            my_ws[key] = globals()[key]
        except TypeError:       
            print('ERROR shelving: {0}'.format(key))