def output(func, *args, **kw):
    """output(func, *args, **kw) -> html string
    Either return the result of a function (which presumably returns an
    HTML-legal string) or a sparse HTMLized error message and a message
    in the server log.
    """
    try:
        return func(*args, **kw)
    except:
        log.msg("Error calling %r:" % (func,))
        log.err()
        return PRE("An error occurred.")
output(func, *args, **kw) -> html string
    Either return the result of a function (which presumably returns an
    HTML-legal string) or a sparse HTMLized error message and a message
    in the server log.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/html.py