Wrong error message in add host process:

Steps:

1. Have an old datacenter with hostname = 'host_yyy' and IP = 'xxx.xxx.xxx.xxx'
2. Try to add a host to a new datacenter in Vcenter, with hostname = 'host_xxx' and IP = 'xxx.xxx.xxx.xxx'

This is how we call addHost:

connectSPEC = vim.host.ConnectSpec(hostName='host_xxx', password=password, userName=userName,
                                               sslThumbprint=sslThumbprint)
             t = self.datacenter.hostFolder.childEntity[0].AddHost_Task(spec=connectSPEC, asConnected=True)
assert task.info.state != vim.TaskInfo.State.error

We get the error:

ERROR root task ClusterComputeResource.addHost completed with state error and error (vim.fault.DuplicateName) {
   dynamicType = <unset>,
   dynamicProperty = (vmodl.DynamicProperty) [],
   msg = "The name 'host_yyy' already exists.",
   faultCause = <unset>,
   faultMessage = (vmodl.LocalizableMessage) [],
   name = 'host_yyy',
   object = 'vim.HostSystem:host-1234'
} 

The error doesn't reflect an IP collision, but a name collision.

Start with the supplied AddHost_Task call and inspect how pyvmomi exposes the returned vim.fault.DuplicateName details. Reproduce the old-datacenter and new-datacenter setup, then determine whether the misleading hostname message originates in pyvmomi or vSphere. Done means identifying the responsible layer and correcting or documenting the reported collision information.