code: def _read_stderr(self):
          
          # We need to read stderr_file as bytes to be able to
          # detect its encoding with chardet
          f = open(self.stderr_file, 'rb')
  
          try:
              stderr_text = f.read()
  
              # This is needed to avoid showing an empty error message
              # when the kernel takes too much time to start.
              # See issue 8581
              if not stderr_text:
                  return ''
  
              # This is needed since the stderr file could be encoded
              # in something different to utf-8.
              # See issue 4191
              encoding = get_coding(stderr_text)
              stderr_text = to_text_string(stderr_text, encoding)
              return stderr_text
          finally:
              f.close()
docs: Read the stderr file of the kernel.