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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 cache_info(cache_dir, cache_key):
 """ Returns the cache files mtime or 0 if it does not exists """

    filename = os.path.join(cache_dir, cache_key)
    return os.path.getmtime(filename) if os.path.exists(filename) else 0