def open(self, filename):
        # type: (str) -> None
        '''
        Open up an existing ISO for inspection and modification.

        Parameters:
         filename - The filename containing the ISO to open up.
        Returns:
         Nothing.
        '''
        if self._initialized:
            raise pycdlibexception.PyCdlibInvalidInput('This object already has an ISO; either close it or create a new object')

        fp = open(filename, 'r+b')
        self._managing_fp = True
        try:
            self._open_fp(fp)
        except Exception:
            fp.close()
            raise
Open up an existing ISO for inspection and modification.

        Parameters:
         filename - The filename containing the ISO to open up.
        Returns:
         Nothing.