How can I get raw USB keyboard data with Python?

Question

I am using PyUSB in Python as I will have to listen an USB port to retrieve data from an electronic card. For the moment, I have to train myself by reading direct input from a small keyboard (USB-connected) connected to a Raspberry-Pi. Of course, I do not want to read the typed String, I expect to get ASCII codes for example. I just don't get how I could read input from my USB-keyboard.

I already found some snippets :

import usb.core
import usb.util

VENDOR_ID = 0x0922
PRODUCT_ID = 0x8003

# find the USB device
device = usb.core.find(idVendor=VENDOR_ID,
                       idProduct=PRODUCT_ID)

# use the first/default configuration
device.set_configuration()
# first endpoint
endpoint = device[0][(0,0)][0]

# read a data packet
attempts = 10
data = None
while data is None and attempts > 0:
    try:
        data = device.read(endpoint.bEndpointAddress,
                           endpoint.wMaxPacketSize)
    except usb.core.USBError as e:
        data = None
        if e.args == ('Operation timed out',):
            attempts -= 1
            continue

print data

Either I get the error 16 "Device is busy" or nothing at all if I uncomment the following line "device.set_configuration()" which causes the "Device is busy" exception... (I did replace VENDOR_ID and PRODUCT_ID with my keyboard's ids)

Mannerly

Your device is used by the OS as input device. You can not use it directly then. You did not give any information of the OS. – Gratulation

Is there a way to detach it from the kernel temporary in order to use it in my python app ? – Mannerly

See the is_kernel_driver_active and detach_kernel_driver methods of the usb device class. The libusb documentation discusses this a bit. – Grane

Answer 1

I'm assuming that you are using Linux, as you mentioned the Raspberry Pi. You can use python-evdev to read data from the event devices in /dev/input/.

For example:

from evdev import InputDevice, categorize, ecodes

device = InputDevice("/dev/input/event3") # my keyboard
for event in device.read_loop():
    if event.type == ecodes.EV_KEY:
        print(categorize(event))

Output:

key event at 1462881252.506405, 30 (KEY_A), up
key event at 1462881252.541371, 31 (KEY_S), up
key event at 1462881252.616399, 31 (KEY_S), down
key event at 1462881252.674422, 22 (KEY_U), down
key event at 1462881252.730418, 31 (KEY_S), up
key event at 1462881252.745558, 22 (KEY_U), up
key event at 1462881252.808419, 50 (KEY_M), down
key event at 1462881252.914552, 23 (KEY_I), down
key event at 1462881252.925388, 50 (KEY_M), up
key event at 1462881253.003579, 49 (KEY_N), down
key event at 1462881253.066418, 34 (KEY_G), down

Allegorist

Actually works with my keyboard as event0, thanks, worked like a charm ! :D – Mannerly

No problem, glad I could help :) – Allegorist