How can if check is some fields exist in a json object ?
  v  = {         
      "f1":"v1",
      "f2":"v2",
      "f3":"v3",
      "f4":"v4",
      "f5":"v5"
    }
I have this code:
if v['f1']:
  print "f1 exists"
elif v['f2']:
  print "f2 exists"
elif v['f3']:
  print "f3 exists"
But sometime, when a field doen't existe, exception is fired and the other test fail. How can I do this test ?
