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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 _headers(self):
 """Ensure the Authorization Header has a valid Access Token."""

        if not self.access_token or not self.access_token_expires:
            self._basic_login()

        elif datetime.now() > self.access_token_expires - timedelta(seconds=30):
            self._basic_login()

        return {'Accept': HEADER_ACCEPT,
                'Authorization': 'bearer ' + self.access_token}