python - Single Ultrasonic Sensor for Raspberry pi 2B+ not functioning from Pi Terminal -

i have been working 4-pin hc-sro4 ultrasonic sensors, 4 @ time. have been developing code make 4 of these sensors work simultaneously , after reorganizing wires installation on project , using basic code run one, cannot make sensor function. code follows:

import rpi.gpio gpio import time  trig1 = 15 echo1 = 13 start1 = 0 stop1 = 0  gpio.setmode(gpio.board) gpio.setwarnings(false) gpio.setup(trig1, gpio.out) gpio.output(trig1, 0)  gpio.setup(echo1, gpio.in) while true:        time.sleep(0.1)         gpio.output(trig1, 1)        time.sleep(0.00001)        gpio.output(trig1, 0)         while gpio.input(echo1) == 0:                start1 = time.time()                print("here")         while gpio.input(echo1) == 1:                stop1 = time.time()                print("also here")        print("sensor 1:")        print (stop1-start1) * 17000  gpio.cleanup() 

after changing wires, sensors, , other components within circuit (including gpio pins) have looked @ code, , added print statements terminal see parts of code running. 1st print statement print("here") executes consistently, second print statementprint("also here") not, , @ loss explanation. in other words, why second while loop not being executed? other questions asked here have not worked problem. appreciated.

thanks, h.

here tutorial gaven macdonald might : https://www.youtube.com/watch?v=xacy8l3lsxi

first of all, while block echo1 == 0 loop forever until echo1 becomes 1. in period of time, code inside executed again , again. wouldn't want set time again , again, can this:

while gpio.input(echo1) == 0:     pass #this here make while loop nothing , check again.  start = time.time() #here set start time.  while gpio.input(echo1) == 1:     pass #doing same thing, looping until condition true.  stop = time.time()  print (stop - start) * 170 #note since both values integers, python multiply value 170. if our values string, python write same string again , again: 170 times. 

also, best practice, should use try except blocks safely exit code. such as:

try:     while true:         #code code code... except keyboardinterrupt: #this check if have pressed ctrl+c     gpio.cleanup()