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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 server_poweroff(host=None,
                    admin_username=None,
                    admin_password=None,
                    module=None):
    '''
    Powers down the managed server.

    host
        The chassis host.

    admin_username
        The username used to access the chassis.

    admin_password
        The password used to access the chassis.

    module
        The element to power off on the chassis such as a blade.
        If not provided, the chassis will be powered off.

    CLI Example:

    .. code-block:: bash

        salt dell dracr.server_poweroff
        salt dell dracr.server_poweroff module=server-1
    '''
    return __execute_cmd('serveraction powerdown',
                         host=host, admin_username=admin_username,
                         admin_password=admin_password, module=module)