With reversing buzzer

from gpiozero import InputDevice, OutputDevice, Robot, Buzzer
from time import sleep, time
import random

sleep(2)

fwdsp = 0.75
bcksp = 0.65

bz=Buzzer(16) # using GPIO16 next to a GRD
bz.off()  # make sure its off, because it is anoying if on!
trig = OutputDevice(4)
echo = InputDevice(17)
boris = Robot(right =(20,21),left =(19,26))
duration = 10
end_time = time() + duration
running = True

sleep(2)

def randtime():
    randtim = random.uniform(0.25, 0.75)
    return randtim


def get_pulse_time():
    pulse_start, pulse_end = 0,0

    trig.on() # sends a burst
    sleep(0.00001)
    trig.off() # stops burst

    while echo.is_active == False:
        pulse_start = time()
    while echo.is_active == True:
        pulse_end = time()

    return pulse_end - pulse_start

def calc_dist(duration):
    speed = 343 # speed of sound in air m / second

    distance = speed * duration /2 # distance is there and back hence divide by 2
    #calcs distance in metres

    return distance


while running:
    duration = get_pulse_time()
    distance = calc_dist(duration)

    if distance < 0.2:
        boris.backward(bcksp)
        bz.on()  # Buzzer on
        sleep(0.2)
        bz.off() # Buzzer off
        trn = random.choice(["L","R"])
        if trn == "L":
            boris.left(randtime())
        else:
            boris.right(randtime())
        sleep(0.5)
    else:
        boris.forward(fwdsp)

    if time() >= end_time:
        running = False
        boris.stop()
    sleep (0.06)
    print("%.4f" % distance )