Defining a file descriptor in python3 - to work with pyudev/evdev

Question

I'm currently trying to detect the connexion of a bluetooth button on a raspberry pi 3 (that part works) and once connected, detect when the button is pressed (that part doesn't work).

I've started with the code provided by evdev and tried to tweak it for my use (see hereunder), but I cannot manage to create the correct file descriptor to use with select (if I correctly understood what's happening).

import functools
import pyudev
import evdev
from select import select

context = pyudev.Context()
monitor = pyudev.Monitor.from_netlink(context)
monitor.filter_by(subsystem='bluetooth')
monitor.start()

fds = {monitor.fileno(): monitor}
finalizers = []

while True:
    r, w, x = select(fds, [], [])

    if monitor.fileno() in r:
        r.remove(monitor.fileno())
        for udev in iter(functools.partial(monitor.poll, 0), None):
            devices = [evdev.InputDevice(fn) for fn in evdev.list_devices()]
            for device in devices:
                if device.name.strip() == 'AB Shutter3':
                    if udev.action == u'add':
                        print('Device added: %s' % udev)
                        fds[dev.fd] = device #This here breaks. dev.fd undefined.
                        break
                    if udev.action == u'remove':
                        print('Device removed: %s' % udev)
                        def helper():
                            global fds
                            fds = {monitor.fileno(): monitor}
                        finalizers.append(helper)
                        break

    for fd in r:
        dev = fds[fd]
        for event in dev.read():
            print(event)


    for i in range(len(finalizers)):
        finalizers.pop()()

The problem is that when I try to add the device, dev.fd is not defined. I've tried to define it, but I've got no idea how to define a file descriptor. What should I do ?

Device added: Device('/sys/devices/platform/soc/3f201000.serial/tty/ttyAMA0/hci0/hci0:64')
Traceback (most recent call last):
  File "dev_status.py", line 27, in <module>
    fds = {dev.fd:device} #This here breaks. dev.fd undefined.
NameError: name 'dev' is not defined

Other information : Raspberry Pi 3 running Raspbian Strech & Python 3.5.3

Also, this is my first question on Stack Overflow, so if anything's missing or could be more detailed, feel free to mention it.

Thanks,

Pôm'

Answer 1

OK, I've managed to find a solution. Here it is, if it can help anybody.

#!/usr/bin/env python3

import functools
import pyudev
import evdev
from select import select

context = pyudev.Context()
monitor = pyudev.Monitor.from_netlink(context)
monitor.filter_by(subsystem='bluetooth')
monitor.start()


fds = {monitor.fileno(): monitor}
time = 0.0

udevices = context.list_devices(subsystem='bluetooth')
link_up = False
for udevice in udevices :
    if udevice.device_type == 'link' and udevice.is_initialized :
        link_up = True
        print('yiha')

evdevices = [evdev.InputDevice(fn) for fn in evdev.list_devices()]

if len(evdevices) > 0:
    for evdevice in evdevices:
        if evdevice.name.strip() == 'AB Shutter3' and link_up:
            print('Device existing: %s' % udevice)
            fds[evdevice.fileno()] = evdevice

while True:
    r, w, x = select(fds, [], [])

    if monitor.fileno() in r:
        for udevice in iter(functools.partial(monitor.poll, 0), None):
            evdevices = [evdev.InputDevice(fn) for fn in evdev.list_devices()]
            for evdevice in evdevices:
                if evdevice.name.strip() == 'AB Shutter3':
                    if udevice.action == u'add':
                        print('Device added: %s' % udevice)
                        fds[evdevice.fileno()] = evdevice
                        break
                    if udevice.action == u'remove':
                        print('Device removed: %s' % udevice)
                        fds.pop(evdevice.fileno(),None) 
                        break

    if evdevice.fileno() in r:
        dev = fds[evdevice.fileno()]
        for event in dev.read():
            if event.type == evdev.ecodes.EV_KEY:
                data = evdev.categorize(event)
                if data.keystate == 1 and data.event.timestamp() - time > 0.05 :
                    if data.scancode == 115:
                        print("Big button")
                    elif data.scancode == 28:
                        print("Small button")
                time = data.event.timestamp()

I'm pretty sure I will look at this in horror in a few months' time, but for the moment, it does the job.