def _write_pattern(self, num_files):
    assert (num_files > 0)
    temp_dir = tempfile.mkdtemp()
    file_name = None
    for _ in range(num_files):
        file_name = self._write_data(directory=temp_dir, prefix='mytemp')
    assert file_name
    file_name_prefix = file_name[:file_name.rfind(os.path.sep)]
    return ((file_name_prefix + os.path.sep) + 'mytemp*')
def _write_pattern(self, num_files):
    assert (num_files > 0)
    temp_dir = tempfile.mkdtemp()
    file_name = None
    for _ in range(num_files):
        file_name = self._write_data(directory=temp_dir, prefix='mytemp')
    assert file_name
    file_name_prefix = file_name[:file_name.rfind(os.path.sep)]
    return ((file_name_prefix + os.path.sep) + 'mytemp*')