docs: def _guess(self, filename):
          """Guess the encoding and decode the content of the file."""
  
          encoding = None
  
          file_size = os.path.getsize(filename)
          # If the file is really big, lets just call it binary.
          # We don't have time to let Python chug through a massive file.
          if not self._is_very_large(file_size):
              with open(filename, "rb") as f:
                  if file_size == 0:
                      encoding = 'ascii'
                  else:
                      encoding = self._detect_buffer_encoding(f)
                      if encoding is None:
                          raise UnicodeDecodeError('None', b'', 0, 0, 'Unicode cannot be detected.')
                      if encoding != BINARY_ENCODE:
                          encoding = self._verify_encoding(encoding)
          else:  # pragma: no cover
              raise UnicodeDecodeError('None', b'', 0, 0, 'Unicode detection is not applied to very large files!')
  
          return encoding