'Tie a parameter'

@tied.setter
def tied(self, value):

    if (self._model is not None):
        if ((not six.callable(value)) and (value not in (False, None))):
            raise TypeError(u'Tied    must    be    a    callable')
        self._model._constraints[u'tied'][self._name] = value
    else:
        raise AttributeError(u"can't    set    attribute    'tied'    on    Parameter    definition")
