CircuitPython code to treat Adafruit Gemma.M0 as a simple combination lock

main.py

# Simple combination lock style code for typing a password.
# (code adapted from the demo code installed on the Gemma.M0 in the
#  swag bags at PyCon 2018)
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS
from digitalio import DigitalInOut, Direction
from touchio import TouchIn
import adafruit_dotstar as dotstar
import board
import time

#
# Configuration stuff here.
#
# touch_pattern - the sequence of inputs to click, e.g. [ 1, 1, 2 ] means
#                 press A1 twice followed by A2
# password_filename - the name of the file holding your password. n.b. Keeping
#                     your login password unencrypted in a mountable usb device
#                     is a bad idea
#

# sequence of touches to match before typing password
touch_pattern = [0, 1, 2, 0]
password_filename = '.password'

# One pixel connected internally!
dot = dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1, brightness=0.2)

# Built in red LED
led = DigitalInOut(board.D13)
led.direction = Direction.OUTPUT

# Capacitive touch on A2
touch0 = TouchIn(board.A0)

# Capacitive touch on A2
touch1 = TouchIn(board.A1)

# Capacitive touch on A2
touch2 = TouchIn(board.A2)

# Used if we do HID output, see below
kbd = Keyboard()
layout = KeyboardLayoutUS(kbd)

######################### HELPERS ##############################

RED = [255, 0, 0]
GREEN = [0, 255, 0]
BLUE = [0, 0, 255]
BLACK = [0, 0, 0]
DEEP_PURPLE = [153, 0, 255]


def show_status(color):
    dot[0] = color
    time.sleep(0.5)
    dot[0] = [0, 0, 0]


def touch_from_int(input_id):
    return eval("touch" + str(input_id))


def check_touch(input_id):
    # check this input
    this_input = touch_from_int(input_id)
    if not this_input.value:
        return False

    # if it's touched, make sure the others aren't
    ids = [0, 1, 2]
    ids.remove(input_id)
    other_inputs = [touch_from_int(i) for i in ids]
    if any([input.value for input in other_inputs]):
        return False
    return True


######################### MAIN LOOP ##############################

entered = []

show_status(BLACK)
while True:
    # Start over if A0 and A2 are touched together
    if touch0.value and touch2.value:
        show_status(BLUE)
        entered = []
        continue

    # Check each of the inputs individually
    for input in [0, 1, 2]:
        if check_touch(input):
            entered.append(input)
            print(entered)

            if len(entered) == len(touch_pattern):
                print("correct length")
                if entered == touch_pattern:
                    print("Pattern matched. Entering password")
                    with open(password_filename) as f:
                        password = f.read()
                    layout.write(password + '\n')
                    show_status(GREEN)
                else:
                    print("Pattern not matched")
                    show_status(RED)
                entered = []
            else:
                show_status(DEEP_PURPLE)