'Sets the sign of this angle.
@param sign: The new sign. C{1} for positive and C{-1} for negative
signs, respectively.
@type sign: C{int}
@raise ValueError: If the C{sign} parameter is not C{-1} or C{1}.'

def setSign(self, sign):

    if (sign not in ((-1), 1)):
        raise ValueError(('bad    sign    (got    %s,    expected    -1    or    1)' % sign))
    self._angle = (sign * abs(self._angle))
