singleton.py misdesign

[Ignalion]

Hello

I just had a little overview to the project and found the file singleton.py with singleinstance class especially.

The design of this class is incorrect because of two things as below:

1. This class has to ensure that lock file is being deleted when app is closed (as far as I understand it). But it won't work. Well, it would, probably, but as it's stated in python doc, it's not guaranteed that __del__ method will ever called. So it can easily lead to situation when lock file remains in system after app shutdown.
2. There is try..except block in __del__ method which would not work ever because, as stated in python doc, any exception that occurs while running __del__ method will be ignored and just printed a warning in stderr instead.

Thus, I'd suggest to either make some other method like release() that should be called directly or redesign this class\idea.

Thanks,
Constantine