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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_subgroups(self, subgroups):
 """ Add a list of SubGroupDefinition objects to this composite. Note that in contrast to :meth:`BaseTrack`, which takes a single dictionary indicating the particular subgroups for the track, this method takes a list of :class:`SubGroupDefinition` objects representing the allowed subgroups for the composite. :param subgroups: List of SubGroupDefinition objects. """

        if subgroups is None:
            subgroups = {}
        _subgroups = {}
        for sg in subgroups:
            assert isinstance(sg, SubGroupDefinition)
            _subgroups[sg.name] = sg
        self.subgroups = _subgroups