def query_yes_no(question, true='yes', false='no'):
    while True:
        print (question + ' [' + true[0] + '/' + false[0] + ']'),
        choice = raw_input().lower()
        if choice in (true, true[0]):
            return True
        if choice in (false, false[0]):
            return False
        else:
            print "Please respond with '" + true + "' or '" + false +\
                  "' (or '" + true[0] + "' or '" + false[0] + "').\n"