from gpiozero import Button, Robot
from time import sleep
from signal import pause

robot = Robot((17, 18), (22, 23))

left = Button(2)
right = Button(3)
forward = Button(4)
backward = Button(5)
go = Button(6)

instructions = []

def add_instruction(btn):
    instructions.append({
        left:     (-1, 1),
        right:    (1, -1),
        forward:  (1, 1),
        backward: (-1, -1),
    }[btn])

def do_instructions():
    instructions.append((0, 0))
    robot.source_delay = 0.5
    robot.source = instructions
    sleep(robot.source_delay * len(instructions))
    del instructions[:]

go.when_pressed = do_instructions
for button in (left, right, forward, backward):
    button.when_pressed = add_instruction

pause()