How to use the graphviz.backend.CalledProcessError function in graphviz

else:
            raise

    out, err = proc.communicate(input)

    if not quiet and err:
        _compat.stderr_write_bytes(err, flush=True)

    if encoding is not None:
        if out is not None:
            out = out.decode(encoding)
        if err is not None:
            err = err.decode(encoding)

    if check and proc.returncode:
        raise CalledProcessError(proc.returncode, cmd,
                                 output=out, stderr=err)

    return out, err

def __str__(self):
        s = super(CalledProcessError, self).__str__()
        return '%s [stderr: %r]' % (s, self.stderr)