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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 _set_label(self, which, label, **kwargs):
 """Private method for setting labels. Args: which (str):
 The indicator of which part of the plots to adjust. This currently handles `xlabel`/`ylabel`, and `title`. label (str):
 The label to be added. fontsize (int, optional):
 Fontsize for associated label. Default is None. """

        prop_default = {
            'fontsize': 18,
        }

        for prop, default in prop_default.items():
            kwargs[prop] = kwargs.get(prop, default)

        setattr(self.label, which, label)
        setattr(self.label, which + '_kwargs', kwargs)
        return