Invalid List Element Type

Getting error when trying to apply an ip address to a created Loopback address.  Any pointers much appreciated. 

The following error is given:- 

ydk.errors.YPYModelError:

  InterfaceConfigurations.interface_configuration: (INVALID_TYPE, Invalid list element type, type = <ydk.models.cisco_ios_xr.Cisco_IOS_XR_ifmgr_cfg.InterfaceConfigurations.InterfaceConfiguration.Ipv4Network.Addresses.Primary object at 0x107521b38>) 

The code I am attempting to run is:- 

from ydk.services import CRUDService

from ydk.providers import NetconfServiceProvider

from ydk.models.cisco_ios_xr import Cisco_IOS_XR_ifmgr_cfg as xr_ifmgr_cfg 

interface_configurations = xr_ifmgr_cfg.InterfaceConfigurations()

interface_configuration = interface_configurations.InterfaceConfiguration()

interface_configuration.active = 'act'
interface_configuration.interface_name = 'Loopback1'
interface_configuration.description = 'A Yang Loopback'

ipv4network = interface_configuration.Ipv4Network.Addresses.Primary()

ipv4network.address = '10.10.10.1'
ipv4network.netmask = '255.255.255.0'

interface_configurations.interface_configuration.append(interface_configuration)

interface_configurations.interface_configuration.append(ipv4network) 

crud.create(provider, interface_configurations)

 Instead of

ipv4network = interface_configuration.Ipv4Network.Addresses.Primary()

 you should have

ipv4network = interface_configuration.Ipv4Network.address.Primary()

Instead of 

 Also, you should indicate that you're creating a virtual interface. See a working example at:

https://git.io/vyNz9

 That should get you going!