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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 custodian_archive(packages=None):
 """Create a lambda code archive for running custodian. Lambda archive currently always includes `c7n` and `pkg_resources`. Add additional packages in the mode block. Example policy that includes additional packages .. code-block:: yaml policy: name: lambda-archive-example resource: s3 mode: packages: - botocore packages: List of additional packages to include in the lambda archive. """

    modules = {'c7n', 'pkg_resources'}
    if packages:
        modules = filter(None, modules.union(packages))
    return PythonPackageArchive(*sorted(modules))