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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 dict( self, *, include: 'SetStr' = None, exclude: 'SetStr' = None, by_alias: bool = False, skip_defaults: bool = False ) -> 'DictStrAny': """ Generate a dictionary representation of the model, optionally specifying which fields to include or exclude. """

        get_key = self._get_key_factory(by_alias)
        get_key = partial(get_key, self.fields)

        return_keys = self._calculate_keys(include=include, exclude=exclude, skip_defaults=skip_defaults)
        if return_keys is None:
            return {get_key(k): v for k, v in self._iter(by_alias=by_alias, skip_defaults=skip_defaults)}
        else:
            return {
                get_key(k): v for k, v in self._iter(by_alias=by_alias, skip_defaults=skip_defaults) if k in return_keys
            }