python 3, try to read from multiple HID inputs, Ra

Question

I have a barcode scanner connected to my RasPi without any tty, which means headless without a monitor. In other words, a keylogger for number inputs. This scanner reads numerical barcodes like GTIN or EAN. It works, the script is started by sh on boot. The script I use looks like that:

import sys

tStr = ''
while 1:
        fp = open('/dev/hidraw3', 'rb')
        buffer = fp.read(8)
        for c in buffer:
                if c:
                        if c == 40 or c == 88: # [ENTER-key]
                                function_to_handle_result (tStr)
                                tStr = ''
                        elif c == 98 or c == 39:
                                c = 0
                                tStr = tStr + str(c)
                        elif c > 29 and c < 39:
                                c = c - 29
                                tStr = tStr + str(c)
                        elif c > 88 and c < 98:
                                c = c - 88
                                tStr = tStr + str(c)

Now I want the user to be able to input numbers manually, in case that the barcode is damaged and/or not readable, and connected a numeric keyboard. Each of these two devices work separately with the script above, if I know the virtual file and its number, like '/dev/hidraw3'.

Now I want to combine the inputs to be able to access the values in one script and one function, and I want to guess the right hidraw-path.

This is my approach, which seems logical to me, but doesn't work. There is no error message, it just does nothing. What am I doing wrong ?

import sys
from pathlib import Path

t = ''

def handle_c(c):
        global t
        if c == 40 or c == 88:
                function_to_handle_result (t)
                t = ''
        elif c == 98 or c == 39:
                c = 0
                t = t + str(c)
        elif c > 29 and c < 39:
                c = c - 29
                t = t + str(c)
        elif c > 88 and c < 98:
                c = c-88
                t = t + str(c)
        return

hid = {}
f = {}
b = {}
c = {}
while 1:
        for i in range(10):
                hid[i] = '/dev/hidraw'+str(i) # guessing path
                if Path(hid[i]).exists(): # check if path exists
                        f[i] = open(hid[i], 'rb')
                        b[i] = f[i].read(8)
                        for c[i] in b[i]:
                                if c[i]:
                                        handle_c(c[i])

In earlier approaches I did not use dynamical variables like here, with the same result, it does nothing.

Thanks for your help.

Answer 1

you can use python-evdev for accessing the numeric keyboard ( and also the barcode scanner ). it is a python implementation of the linux evdev interface that is based on events generated by the input devices, i.e. HID ( https://en.wikipedia.org/wiki/Evdev )

http://python-evdev.readthedocs.io/en/latest/tutorial.html ( for multiple devices see Reading events from multiple devices )

in https://khanhicetea.com/post/read_input_from_usb_keyboard_in_linux/ is code for using evdev with barcode scanner