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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 grains():
    '''
    Get grains for proxy minion

    .. code-block: bash

        salt '*' onyx.cmd grains
    '''
    if not DETAILS['grains_cache']:
        ret = system_info()
        log.debug(ret)
        DETAILS['grains_cache'].update(ret)
    return {'onyx': DETAILS['grains_cache']}