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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 extra(self, **kwargs):
 """ Add extra keys to the request body. Mostly here for backwards compatibility. """

        s = self._clone()
        if 'from_' in kwargs:
            kwargs['from'] = kwargs.pop('from_')
        s._extra.update(kwargs)
        return s