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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 _combine_variant_collections(cls, combine_fn, variant_collections, kwargs):
 """ Create a single VariantCollection from multiple different collections. Parameters cls : class Should be VariantCollection combine_fn : function Function which takes any number of sets of variants and returns some combination of them (typically union or intersection). variant_collections : tuple of VariantCollection kwargs : dict Optional dictionary of keyword arguments to pass to the initializer for VariantCollection. """

        kwargs["variants"] = combine_fn(*[set(vc) for vc in variant_collections])
        kwargs["source_to_metadata_dict"] = cls._merge_metadata_dictionaries(
            [vc.source_to_metadata_dict for vc in variant_collections])
        kwargs["sources"] = set.union(*([vc.sources for vc in variant_collections]))
        for key, value in variant_collections[0].to_dict().items():
            # If some optional parameter isn't explicitly specified as an
            # argument to union() or intersection() then use the same value
            # as the first VariantCollection.
            #
            # I'm doing this so that the meaning of VariantCollection.union
            # and VariantCollection.intersection with a single argument is
            # the identity function (rather than setting optional parameters
            # to their default values.
            if key not in kwargs:
                kwargs[key] = value
        return cls(**kwargs)