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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 set_boot_arch(arch='default'):
    '''
    Set the kernel to boot in 32 or 64 bit mode on next boot.

    .. note::
        When this function fails with the error ``changes to kernel
        architecture failed to save!``, then the boot arch is not updated.
        This is either an Apple bug, not available on the test system, or a
        result of system files being locked down in macOS (SIP Protection).

    :param str arch: A string representing the desired architecture. If no
        value is passed, default is assumed. Valid values include:

        - i386
        - x86_64
        - default

    :return: True if successful, False if not
    :rtype: bool

    CLI Example:

    .. code-block:: bash

        salt '*' system.set_boot_arch i386
    '''
    if arch not in ['i386', 'x86_64', 'default']:
        msg = 'Invalid value passed for arch.\n' \
              'Must be i386, x86_64, or default.\n' \
              'Passed: {0}'.format(arch)
        raise SaltInvocationError(msg)

    cmd = 'systemsetup -setkernelbootarchitecture {0}'.format(arch)
    __utils__['mac_utils.execute_return_success'](cmd)

    return __utils__['mac_utils.confirm_updated'](
        arch,
        get_boot_arch,
    )