python midi repeater with dynamic usb via udev

midirepeater.py

#!/usr/bin/python
import pyudev
import select
import functools
import re
import os
import codecs

fds = {}
devs = {}

def handle_udev_event(action, device):
	global fds
	global devs

	if not device.device_node:
		return

	if not re.match(u"^/dev/midi[0-9]+$", device.device_node):
		return

	node = device.device_node
	#print('ACTION={0}: DEVICE={1} SUBSYSTEM={2} TAGS={3}'.format(action, device, device.subsystem, list(device.tags)))
	if action == "remove":
		if node in devs.keys():
			if devs[node] in fds.keys():
				del fds[devs[node]]
			os.close(devs[node])
			print("removed "+node+" closed fd "+str(devs[node]))
			del devs[node]
	elif action == "add":
		if node not in devs.keys():
			fd = os.open(node, os.O_RDWR)
			devs[node] = fd
			fds[fd] = bytearray(0)
			print("added "+node+" opened fd "+str(fd))

context = pyudev.Context()
for device in iter(context.list_devices(subsystem='sound')):
	handle_udev_event('add', device)

monitor = pyudev.Monitor.from_netlink(context)
monitor.filter_by(subsystem='sound')
monitor.enable_receiving()


while True:
	reading = [monitor.fileno()] + list(fds.keys())
	writing = [k for k in fds.keys() if len(fds[k]) > 0]
	trying = reading
	readable, writable, exceptional = select.select(reading, writing, trying)

	if monitor.fileno() in readable:
		readable.remove(monitor.fileno())

		for udev in iter(functools.partial(monitor.poll, 0), None):
			handle_udev_event(udev.action, udev)

	for f in writable:
		n = os.write(f, fds[f])
		print("Wrote %d bytes to descriptor %d: %s" % (n, f, codecs.encode(bytes(fds[f][:n]), 'hex')))
		fds[f] = fds[f][n:]

	for f in readable:
		b = bytearray(os.read(f, 1024))
		print("Read %d bytes from descriptor %d: %s" % (len(b), f, codecs.encode(bytes(b), 'hex')))
		for g in fds.keys():
			if not (g == f):
				fds[g] = fds[g] + b


#for action, device in monitor:
#	handle_udev_event(action, device)