def _index_file(self):
        """Open and index the contour file

        This function populates the internal list of contours
        as strings which will be available as `self.data`.
        """
        with self.filename.open() as fd:
            data = fd.read()

        ident = "Contour in frame"
        self._data = data.split(ident)[1:]
        self._initialized = True
Open and index the contour file

        This function populates the internal list of contours
        as strings which will be available as `self.data`.