docs: def tee2(process, filter):
      """Read lines from process.stderr and echo them to sys.stderr.
  
      The 'filter' is a callable which is invoked for every line,
      receiving the line as argument. If the filter returns True, the
      line is echoed to sys.stderr.
      """
      while True:
          line = process.stderr.readline()
          if line:
              if sys.version_info[0] >= 3:
                  line = decode(line)
              stripped_line = line.rstrip()
              if filter(stripped_line):
                  sys.stderr.write(line)
          elif process.returncode is not None:
              process.stderr.close()
              break