tryton.cfg:

    [tryton]
    version=3.9.0
    depends:
        ir
        res
    extras_depend:
        party

party.py:

    class Party:
        __metaclass__ = PoolMeta
        __name__ = 'party.party'

        website = fields.Function(
            fields.Char('Website'), 'get_mechanism', setter='set_mechanism')

        @classmethod
        def __setup__(cls):
            super(Party, cls).__setup__()
            setter = 'set_mechanism'
            cls.phone.setter = setter # doesn't work
            del cls.website # works

        @classmethod
        def set_mechanism(cls, parties, name, value):
            pass