Using YDK bgp sessions.session giving output empty list

Using YDK,trying to get output of bgp sessions.session (equivalent CLI - show bgp sessions)

 Script

--------

from ydk.services import CRUDService,CodecService

from ydk.providers import NetconfServiceProvider,CodecServiceProvider

from ydk.models.cisco_ios_xr import Cisco_IOS_XR_shellutil_oper as xr_shellutil_oper

from ydk.models.cisco_ios_xr import Cisco_IOS_XR_ipv4_bgp_oper

from ydk.models.cisco_ios_xr import Cisco_IOS_XR_ipv4_bgp_datatypes

from datetime import timedelta

from ydk.types import READ 

provider = NetconfServiceProvider(address="192.168.10.10",

                                  username="user1",

                                  password="pass1",

                                  protocol="ssh") 

crud = CRUDService() 

q_instance = Cisco_IOS_XR_ipv4_bgp_oper.Bgp.Instances.Instance()

q_instance.instance_name = 'default' 

q_instances = Cisco_IOS_XR_ipv4_bgp_oper.Bgp.Instances()

q_instances.instance.append(q_instance) 

instances = crud.read(provider, q_instances)

for inst in instances.instance:

    print('Instance: %s' % inst.instance_name)

    default_vrf = inst.instance_active.default_vrf

    print dir(default_vrf)

    print dir(default_vrf.sessions.session) 

    for n in default_vrf.sessions.session:

        print "done"

        node=n.neighbor_address

        print('    neighbor %s' % n.neighbor_address)

        print('        remote-as: %s' % n.remote_as) 

provider.close() 

Script output after executing

----------------------------------------

fabric@FabricAutomation:~/jay$ sudo python bgp_einar.py

Instance: default []           

----------------------------------------------------------------------------------------------------> Empty list we are getting.

fabric@FabricAutomation:~/jay$

What XR version are you using on the device?  What YDK version are you using (pip list | grep ydk)?  Your script provides this output for me on a device running XR 6.2.1:

 Instance: default

['Afs', 'Bmp', 'GlobalProcessInfo', 'Information', 'MessageLogs', 'NeighborRanges', 'Neighbors', 'NextHopVrf', 'Postits', 'ProcessInfo', 'Sessions', 'UpdateInboundErrorNeighbors', 'UpdateInboundErrorVrf', 'UpdateInboundFilterNeighbors', 'UpdateInboundFilterVrf', '__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_common_path', '_has_data', '_meta_info', '_prefix', '_revision', 'afs', 'bmp', 'global_process_info', 'i_meta', 'information', 'is_config', 'message_logs', 'neighbor_ranges', 'neighbors', 'next_hop_vrf', 'parent', 'postits', 'process_info', 'sessions', 'update_inbound_error_neighbors', 'update_inbound_error_vrf', 'update_inbound_filter_neighbors', 'update_inbound_filter_vrf']
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__delslice__', '__dict__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__module__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__setslice__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'append', 'count', 'extend', 'index', 'insert', 'name', 'parent', 'pop', 'remove', 'reverse', 'sort']
done
    neighbor 172.16.255.2
        remote-as: 65001

It was run against an XRv9K (virtual) router running XR 6.2.1.  
What version of software are you using on your device. What is your BGP CLI configuration.

Have verified on NCS5500 series router and get the empty list (None value)for the same script. Want to know the details which router model verified the above script.

The issue here isn't really related to YDK.  It seems to be specific to the hardware/software combination on your router.  The XR engineering team should be able to provide a fix.

RP/0/RP0/CPU0:l1#show version

Thu Apr 20 00:33:14.841 EDT 

Cisco IOS XR Software, Version 6.1.31.13I

Copyright (c) 2013-2016 by Cisco Systems, Inc. 

Build Information:

Built By     : hlo

Built On     : Thu Apr 13 23:56:37 PDT 2017

Build Host   : iox-lnx-049

Workspace    : /auto/iox-lnx-049-san1/production/6.1.31.13I.DT_IMAGE/ncs5500/workspace

Version      : 6.1.31.13I

Location     : /opt/cisco/XR/packages/ 

cisco NCS-5500 () processor

System uptime is 5 hours, 14 minutes 

RP/0/RP0/CPU0:# 

YDK version is 6.2.1 

Here router version is 6.1.31 and YDK version is 6.2.1 . 

Is it due to version mismatch , because our script is working with your virtual router . 

No, it's not due to version difference.  It's related to a software defect in your version of Cisco IOS XR.  That defect isn't present in 6.2.1.  Asmentioned before, the XR engineers will provide a fix.