docs: def get_mirrors(hostname=None):
      """Return the list of mirrors from the last record found on the DNS
      entry::
  
      >>> from pip.index import get_mirrors
      >>> get_mirrors()
      ['a.pypi.python.org', 'b.pypi.python.org', 'c.pypi.python.org',
      'd.pypi.python.org']
  
      Originally written for the distutils2 project by Alexis Metaireau.
      """
      if hostname is None:
          hostname = DEFAULT_MIRROR_URL
  
      # return the last mirror registered on PyPI.
      try:
          hostname = socket.gethostbyname_ex(hostname)[0]
      except socket.gaierror:
          return []
      end_letter = hostname.split(".", 1)
  
      # determine the list from the last one.
      return ["%s.%s" % (s, end_letter[1]) for s in string_range(end_letter[0])]