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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 token_cache_pkgs(source=None, release=None):
 """Determine additional packages needed for token caching @param source: source string for charm @param release: release of OpenStack currently deployed @returns List of package to enable token caching """

    packages = []
    if enable_memcache(source=source, release=release):
        packages.extend(['memcached', 'python-memcache'])
    return packages