def _get_requested_diff_file(self, diffset, filediff, interdiffset):
        """Fetches information on the requested diff.

        This will look up information on the diff that's to be rendered
        and return it, if found. It may also augment it with additional
        data.

        The file will not contain chunk information. That must be specifically
        populated later.
        """
        files = get_diff_files(diffset, filediff, interdiffset,
                               request=self.request)

        if files:
            assert len(files) == 1
            file = files[0]

            if 'index' in self.request.GET:
                try:
                    file['index'] = int(self.request.GET.get('index'))
                except __HOLE__:
                    pass

            return file

        return None
dataset/ETHPy150Open reviewboard/reviewboard/reviewboard/diffviewer/views.py/DiffFragmentView._get_requested_diff_file