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def get_access_token(self):

    if self._token:
        now = time.time()
        if ((self.token_expires_at - now) > 60):
            return self._token
    json = self.grant_token()
    self._token = json['access_token']
    self.token_expires_at = (int(time.time()) + json['expires_in'])
    return self._token
