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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 key_changes(self, from_token, to_token):
 """Gets a list of users who have updated their device identity keys. Args: from_token (str):
 The desired start point of the list. Should be the next_batch field from a response to an earlier call to /sync. to_token (str):
 The desired end point of the list. Should be the next_batch field from a recent call to /sync - typically the most recent such call. """

        params = {"from": from_token, "to": to_token}
        return self._send("GET", "/keys/changes", query_params=params)