Modifying virtual machine custom attributes values using pyvmomi

There is a discussion https://communities.vmware.com/thread/474322?start=0&tstart=0 which talks about creating virtual machine custom attribute using pyvmomi.

I want to set and get virtual machine custom attribute values using pyvmomi. What are the steps I can take to do that. 

For example I create a custom attribute like this

Name : owner

Type : Virtual Machine

Value : {not set}

I want steps to set the value to "Tom" for a specific vm whose name is "myvm". Then read the value for the vm "myvm" to check if it is still "Tom".