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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 set_cache_expiry(response):
 """ Set the cache control headers """

    if response.cache_control.max_age is None and 'CACHE_DEFAULT_TIMEOUT' in config.cache:
        response.cache_control.max_age = config.cache['CACHE_DEFAULT_TIMEOUT']
    return response