How do I use try, except?

I am currently making a program for the raspberry pi2 I just brought and with the help from some other members, have got it to work most of the time. however there are some case where it won't work because a field doesnt exist in the json if im correct. the code i have is:

import urllib.request
import json

r = urllib.request.urlopen("http://ift.tt/1NTgHGN").read()
rr = r.decode()

obj = json.loads(rr)

# filter only the b16 objects
b16_objs = filter(lambda a: a['routeName'] == 'B16',  obj['arrivals'])

if b16_objs:
# get the first item
b16 = next(b16_objs)
my_estimatedWait = b16['estimatedWait']

my_destination = b16['destination']
print(my_estimatedWait)

My problem is that when routeName B16 is not in the json, an error comes up. I've tried to use the try and catch feature but I could not get this to work. Is there another way of catching this error and displaying a message saying its not present?

The try and catch

try:
b16 = next(b16_objs)
except:
print("there are no records of this")

via Chebli Mohamed