Pylint pass for midi module

[MyreMylar]

Tested using: pylint src_py/midi.py

This PR reduces the pylint warnings down to this list:

src_py\midi.py:18:2: W0511: TODO: finish writing tests. (fixme)
src_py\midi.py:21:2: W0511: TODO: create a background thread version for input threads. (fixme)
src_py\midi.py:103:2: W0511: TODO: find all Input and Output classes and close them first? (fixme)
src_py\midi.py:377:45: W0613: Unused argument 'buffer_size' (unused-argument)

Three TODOs, which are beyond the scope of a pylint pass, and one genuine error in the public interface. It appears that the buffer_size parameter passed to the midi.Output class is never used at all.

I'll raise a separate issue about the buffer_size parameter.

Disabled:

def quit(): # pylint: disable=redefined-builtin

This is a sort of generic problem across all pygame modules - that their quit functions shadow python's built-in quit() function. For example, if you do:

from pygame.midi import *

quit()

You will call the pygame.midi modules quit() function rather than the built-in quit() function. I don't think we can change this at this point, all those module quit() functions are out there now.

[MyreMylar]

I did some weird code to avoid having to use the global keyword for module level state here:

def _module_init(state=None):
    # this is a sneaky dodge to store module level state in a non-public
    # function. Helps us dodge using globals.
    if state is not None:
        _module_init.value = state
        return state

    try:
        _module_init.value
    except AttributeError:
        return False
    else:
        return _module_init.value

I'm not particularly happy about it, though it does work.

The standard advice for getting rid of mutable globals is to transform the code using them into a class, but that isn't really an option here because the midi module is already in widespread use. Thus we come back to this. Does anyone have a cleaner way to purge globals like this?

[illume]

Nice cleanups. Thanks 👍