Flask application to write the specified value to a HID device (RPI Zero in my case)

app.py

import time
import sys
from flask import Flask
from flask import request

NULL_CHAR = chr(0)
EOL_SEQ = NULL_CHAR*5
RELEASE_SEQ = NULL_CHAR*8

KEYMAP = {
    'a': 0x04, 'A': 0x04, # Keyboard a and A
    'b': 0x05, 'B': 0x05, # Keyboard b and B
    'c': 0x06, 'C': 0x06, # Keyboard c and C
    'd': 0x07, 'D': 0x07, # Keyboard d and D
    'e': 0x08, 'E': 0x08, # Keyboard e and E
    'f': 0x09, 'F': 0x09, # Keyboard f and F
    'g': 0x0a, 'G': 0x0a, # Keyboard g and G
    'h': 0x0b, 'H': 0x0b, # Keyboard h and H
    'i': 0x0c, 'I': 0x0c, # Keyboard i and I
    'j': 0x0d, 'J': 0x0d, # Keyboard j and J
    'k': 0x0e, 'K': 0x0e, # Keyboard k and K
    'l': 0x0f, 'L': 0x0f, # Keyboard l and L
    'm': 0x10, 'M': 0x10, # Keyboard m and M
    'n': 0x11, 'N': 0x11, # Keyboard n and N
    'o': 0x12, 'O': 0x12, # Keyboard o and O
    'p': 0x13, 'P': 0x13, # Keyboard p and P
    'q': 0x14, 'Q': 0x14, # Keyboard q and Q
    'r': 0x15, 'R': 0x15, # Keyboard r and R
    's': 0x16, 'S': 0x16, # Keyboard s and S
    't': 0x17, 'T': 0x17, # Keyboard t and T
    'u': 0x18, 'U': 0x18, # Keyboard u and U
    'v': 0x19, 'V': 0x19, # Keyboard v and V
    'w': 0x1a, 'W': 0x1a, # Keyboard w and W
    'x': 0x1b, 'X': 0x1b, # Keyboard x and X
    'y': 0x1c, 'Y': 0x1c, # Keyboard y and Y
    'z': 0x1d, 'Z': 0x1d, # Keyboard z and Z

    '1': 0x1e, '!': 0x1e, # Keyboard 1 and !
    '2': 0x1f, '@': 0x1f, # Keyboard 2 and @
    '3': 0x20, '#': 0x20, # Keyboard 3 and #
    '4': 0x21, '$': 0x21, # Keyboard 4 and $
    '5': 0x22, '%': 0x22, # Keyboard 5 and %
    '6': 0x23, '^': 0x23, # Keyboard 6 and ^
    '7': 0x24, '&': 0x24, # Keyboard 7 and &
    '8': 0x25, '*': 0x25, # Keyboard 8 and *
    '9': 0x26, '(': 0x26, # Keyboard 9 and (
    '0': 0x27, ')': 0x27, # Keyboard 0 and )

    'ENTER': 0x28, # Keyboard Return (ENTER)
    'ESC': 0x29, # Keyboard ESCAPE
    'BACKSPACE': 0x2a, # Keyboard DELETE (Backspace)
    'TAB': 0x2b, # Keyboard Tab
    'SPACE': 0x2c, ' ': 0x2c, # Keyboard Spacebar
    'MINUS': 0x2d, '-': 0x2d,# Keyboard - and _
    'EQUAL': 0x2e, '=': 0x2e, # Keyboard = and +
    'LEFTBRACE': 0x2f, # Keyboard [ and {
    'RIGHTBRACE': 0x30, # Keyboard ] and }
    'BACKSLASH': 0x31, # Keyboard \ and |
    'HASHTILDE': 0x32, # Keyboard Non-US # and ~
    'SEMICOLON': 0x33, # Keyboard ; and :
    'APOSTROPHE': 0x34, # Keyboard ' and "
    'GRAVE': 0x35, # Keyboard ` and ~
    'COMMA': 0x36, # Keyboard , and <
    'DOT': 0x37, '.': 0x37, # Keyboard . and >
    'SLASH': 0x38, '/': 0x38, # Keyboard / and ?
    'CAPSLOCK': 0x39, # Keyboard Caps Lock
}

# Get the keyboard ASCII character for the provided character.
def get_chr(input):
    if input in KEYMAP:
        return chr(KEYMAP[input])
    return None

# Get the key sequence for a string.
def get_seq(value):
    result = ""

    for v in value:
        k = v
        
        if(v.isupper()):
            result += chr(32)+NULL_CHAR # Uppercase character, press shift
            k = k.lower()
        else:
            result += NULL_CHAR*2

        val = get_chr(k)
        result += val
        result += EOL_SEQ

    return result

# Write the specified sequence to the HID.
def write_hid(seq):
    with open('/dev/hidg0', 'rb+') as fd:
        fd.write(seq.encode())

app = Flask(__name__)

@app.route("/")
def index():
    msg = request.args.get('msg')
    seq = get_seq(msg)
    if request.args.get('crlf'):
        seq += NULL_CHAR*2 + chr(0x28) + EOL_SEQ
    write_hid(seq + RELEASE_SEQ)
    return msg