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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 fetch_all_droplets(self, tag_name=None):
 r""" Returns a generator that yields all of the droplets belonging to the account .. versionchanged:: 0.2.0 ``tag_name`` parameter added :param tag_name: if non-`None`, only droplets with the given tag are returned :type tag_name: string or `Tag` :rtype: generator of `Droplet`\ s :raises DOAPIError: if the API endpoint replies with an error """

        params = {}
        if tag_name is not None:
            params["tag_name"] = str(tag_name)
        return map(self._droplet, self.paginate('/v2/droplets', 'droplets',
                                                params=params))