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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 cpu():
    '''
    Tests for the CPU performance of minions.

    CLI Examples:

    .. code-block:: bash

        salt '*' sysbench.cpu
    '''

    # Test data
    max_primes = [500, 1000, 2500, 5000]

    # Initializing the test variables
    test_command = 'sysbench --test=cpu --cpu-max-prime={0} run'
    result = None
    ret_val = {}

    # Test beings!
    for primes in max_primes:
        key = 'Prime numbers limit: {0}'.format(primes)
        run_command = test_command.format(primes)
        result = __salt__['cmd.run'](run_command)
        ret_val[key] = _parser(result)

    return ret_val