'Check that a foreign object is suitable for use in the comparison or
arithmetic magic methods of this L{SerialNumber} instance. Raise
L{TypeError} if not.
@param other: The foreign L{object} to be checked.
@return: C{other} after compatibility checks and possible coercion.
@raises: L{TypeError} if C{other} is not compatible.'

def _convertOther(self, other):

    if (not isinstance(other, SerialNumber)):
        raise TypeError(('cannot    compare    or    combine    %r    and    %r' % (self, other)))
    if (self._serialBits != other._serialBits):
        raise TypeError(('cannot    compare    or    combine    SerialNumber    instances    with    different    serialBits.    %r    and    %r' % (self, other)))
    return other
