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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 config_set(key, value):
    '''
    Set an LXD daemon config option

    CLI Examples:

    To listen on IPv4 and IPv6 port 8443,
    you can omit the :8443 its the default:

    .. code-block:: bash

        salt '*' lxd.config_set core.https_address [::]:8443

    To set the server trust password:

    .. code-block:: bash

        salt '*' lxd.config_set core.trust_password blah

    '''
    cmd = 'lxc config set "{0}" "{1}"'.format(
        key,
        value,
    )

    output = __salt__['cmd.run'](cmd)
    if 'error:' in output:
        raise CommandExecutionError(
            output[output.index('error:') + 7:],
        )

    return 'Config value "{0}" successfully set.'.format(key),