def _read_tempfile(self, filename):
        '''Read in and return file that's in the tempdir.

        :param filename: Name of the file to read.
        :type filename: str

        '''
        with open(os.path.join(self._tempdir, filename)) as f:
            return f.read()
Read in and return file that's in the tempdir.

        :param filename: Name of the file to read.
        :type filename: str