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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 roster(opts, runner=None, utils=None, whitelist=None):
    '''
    Returns the roster modules
    '''
    return LazyLoader(
        _module_dirs(opts, 'roster'),
        opts,
        tag='roster',
        whitelist=whitelist,
        pack={
            '__runner__': runner,
            '__utils__': utils,
        },
    )