class FilterModule:
    def map_dict_values_to_subkey(self, m, subkey):
        return dict([
            (key, value[subkey])
            for key, value in m.items()
            if subkey in value
        ])

    def sort_dict_by_keys(self, d):
        return dict([(key,d[key]) for key in sorted(d.keys())])

    def dict_slice(self, dict, keys):
        for key in keys:
            yield dict[key]

    def filters(self):
        return {
            'map_dict_values_to_subkey': self.map_dict_values_to_subkey,
            'sort_dict_by_keys': self.sort_dict_by_keys,
            'dict_slice': self.dict_slice,
        }