code: def _read_python_source(self, filename):
          
          try:
              f = open(filename, "rb")
          except IOError as err:
              self.log_error("Can't open %s: %s", filename, err)
              return None, None
          try:
              encoding = tokenize.detect_encoding(f.readline)[0]
          finally:
              f.close()
          with _open_with_encoding(filename, "r", encoding=encoding) as f:
              return _from_system_newlines(f.read()), encoding
docs: Do our best to decode a Python source file correctly.