def concat_keys_and_values(keys, vals):
    """ Format keys and values in string.
  e.g.
    keys = ['a', 'b', 'c']
    vals = [4, 5, 6]
    str = 'a:4, b:5, c:6'
  """
    fmt = ''
    for tup in zip(keys, vals):
        fmt += ', {0}: {1}'.format(tup[0], tup[1])
    return fmt
