I was trying to get +python to work on Windows, however I found there was problem with the implementation of the system() function, called by the python provider. The problem can be produced like this:

For the following vim command:

:echo system('python -c ' . '"print(''a''); print(''b'')"')

Vim gives the expected result, but Neovim gives this:

  File "<string>", line 1
    "print('a');
               ^
SyntaxError: EOL while scanning string literal

I think the problem may be related with quoting.

Thanks & best regards!