docs: def parse_tz(tz):
      """Parse a timezone specification in the [+|-]HHMM format.
  
      :return: the timezone offset in seconds.
      """
      # from git_repository.py in bzr-git
      sign_byte = tz[0:1]
      # in python 3 b'+006'[0] would return an integer,
      # but b'+006'[0:1] return a new bytes string.
      if sign_byte not in (b'+', b'-'):
          raise ValueError(tz)
  
      sign = {b'+': +1, b'-': -1}[sign_byte]
      hours = int(tz[1:-2])
      minutes = int(tz[-2:])
  
      return sign * 60 * (60 * hours + minutes)