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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 _refresh(self, _):
 """Refresh self.access_token. Args: _: (ignored) A function matching httplib2.Http.request's signature. """

        # pylint: disable=import-error
        from google.appengine.api import app_identity
        try:
            token, _ = app_identity.get_access_token(self._scopes)
        except app_identity.Error as e:
            raise exceptions.CredentialsError(str(e))
        self.access_token = token