def _write_export(export, file_obj=None):
    """
    Write a string to a file.
    If file_obj isn't specified, return the string

    Parameters
    ---------
    export: a string of the export data
    file_obj: a file-like object or a filename
    """
    if file_obj is None:
        return export
    if hasattr(file_obj, 'write'):
        out_file = file_obj
    else:
        out_file = open(file_obj, 'wb')
    try:
        out_file.write(export)
    except TypeError:
        out_file.write(export.encode('utf-8'))
    out_file.close()
    return export
