Python library: evdev

Monitor an input device

The following command must likely be executed as root:

python -m evdev.evtest

InputDevice

evdev.InputDevice represents an input device (think /dev/input/eventX) from which input events can be read.

`__init__`
`path`	The device that the instance is reading from (`/dev/input/eventX`)
`fd`	Likely a file descriptor
`info`	An instance of `device.DeviceInfo`
`name`
`phys`	A string whose value is something like `isa0060/serio0/input0`
`uniq`	A string
`version`	An `int`
`ff_effects_count`	An `int`
`capabilities()`
`input_props`	A `list`
`leds()`
`set_led()`
`__eq__`
`__ne__`
`__fspath__`
`grab`, `ungrab`	Exclusively grab (or release) a device (`EVIOCGRAB`).
`grab_context`	A context manager that calls `ungrab()` when the corresponding `with` block is exited.
`upload_effect`
`erase_effect`
`repeat`
`active_keys()`
`fn`
`absinfo`
`__hash__`

UInput

evdev.UInput …

events.InputEvent

Instances of InputEvent are returned by EventIO.read_loop() and EventIO.read().

The evdev.events.InputEvent resemples the struct input_event found in include/uapi/linux/input.h.

The module also defines specific subtypes depending on the type of an event (key, abs, rel etc.) (see also the util.categorize function and the event_factory dictionary).

Such subclasses include

`InputEvent`	A generic event
`KeyEvent`	An event generated by a keyboard or other key-like devices
`RelEvent`	An event generated by devices with relative movements (like mice)
`AbsEvent`

eventio.EventIO

Used by evdev.InputEvent for reading, by UInput for writing events.

Methods in this class seem to be:

`fileno`
`read_loop`	Indefinitely returns `InputEvent` instances.
`read_one`	returns an instance of `InputEvent`
`read`
`need_write`
`write_event`, `write`	Injects an event into the input subsystem.
`close`

ecodes

Dictionaries with constants defined in include/uapi/linux/input-event-codes.h and linux/input.h (more likely include/uapi/linux/input.h than include/linux/input.h - even though the latter includes the former).

from evdev import ecodes

for ecode in dir(ecodes):
    print(ecode + ': ' + str(type(getattr(ecodes, ecode))))

ecodes.EV

from evdev import ecodes

for ev in ecodes.EV:
    print(f"{ecodes.EV[ev]:<14} {ev}")
#
# EV_ABS         3
# EV_CNT         32
# EV_FF          21
# EV_FF_STATUS   23
# EV_KEY         1
# EV_LED         17
# EV_MAX         31
# EV_MSC         4
# EV_PWR         22
# EV_REL         2
# EV_REP         20
# EV_SND         18
# EV_SW          5
# EV_SYN         0
# EV_UINPUT      257
# EV_VERSION     65537

It seems that the values if ecodes.EV can be used to determine the event type:

import evdev
device = evdev.InputDevice('/dev/input/event7')

for event in device.read_loop():
    if   event.type == evdev.ecodes.EV_KEY:
         print(evdev.categorize(event))
    elif event.type == evdev.ecodes.EV_SYN:
         print('SYN event')
    else:
        print('Event type: ' + str(event.type))

device.DeviceInfo

`bustype`
`vendor`
`product`
`version`

When the instance is printed, it produces a value like bus: 0011, vendor 0001, product 0001, version abba.

util

Functions offered by evdev.util include:

`list_devices()`	Returns a list of strings each of which is areadable devices in a given directory (default directory of course is `/dev/input`).
`is_device`	Checks if a device is a readable and writeable character device.
`categorize`	Categorizes an event according to its type. This function is somehow related to the `event_factory` dictionary which maps event types to subclasses of `InputEvent`.
`resolve_evcodes`	Resolves event codes and types to their verbose names.
`resolve_ecodes_dict`

Misc

Find a device by a given name

The following snippet uses a nested list comprehension to find a device object of an input device with a given name:

import evdev

devname = 'LITEON Technology USB Multimedia Keyboard'
        # 'AT Translated Set 2 keyboard'

devobjs = [ devobj for devobj  in [ evdev.InputDevice(devpath) 
                   for devpath in evdev.list_devices() ]
              if devobj.name == devname
          ]

if devobjs == []:
   print('no device found')
   quit()

devobj=devobjs[0]

print(devobj)

Print named constants of pressed keys

import evdev

devname = 'LITEON Technology USB Multimedia Keyboard'

devobjs = [ devobj for devobj  in [ evdev.InputDevice(devpath) 
                   for devpath in evdev.list_devices() ]
              if devobj.name == devname
          ]

if devobjs == []:
   print('no device found')
   quit()

devobj=devobjs[0]

for ev in devobj.read_loop():
    if ev.type == evdev.ecodes.EV_KEY and ev.value == 1:
       print(evdev.ecodes.KEY[ev.code])