How to set Default Node Monitor - Python f5-SDK

I am trying to set the default node monitor using the F5-SDK.

Here's the code I've tried

from f5.bigip import ManagementRoot
mgmt = ManagementRoot('ip address', 'user', 'password')
mgmt.tm.ltm.defaut_node_monitor.update(rule='/Common/gateway_icmp')

When navigating the API in a browser I see the default-node-monitor is a resource, the update method should work according to the SDK documentation.

https://localhost/mgmt/tm/ltm/default-node-monitor

{
    kind: "tm:ltm:default-node-monitor:default-node-monitorstate",
    selfLink: "https://localhost/mgmt/tm/ltm/default-node-monitor?ver=12.1.2"
}

If I change the default node monitor in the config utility and navigate the API, I notice the rule attribute for the default-node-monitor is changed

{
    kind: "tm:ltm:default-node-monitor:default-node-monitorstate",
    selfLink: "https://localhost/mgmt/tm/ltm/default-node-monitor?ver=12.1.2",
    rule: "/Common/gateway_icmp "
}