def open(self, mode):
        """
        If the mode is r+, return a L{_ReadFile} with the contents given to
        this path's initializer.

        @raise OSError: If the mode is unsupported.

        @return: A L{_ReadFile} instance
        """
        if mode == "rb+":
            return _ReadFile(self.contents)
        raise OSError(ENOSYS, "Function not implemented")

        If the mode is r+, return a L{_ReadFile} with the contents given to
        this path's initializer.

        @raise OSError: If the mode is unsupported.

        @return: A L{_ReadFile} instance
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_endpoints.py