Traceback (most recent call last):
  File "/usr/bin/nova-api", line 42, in <module>
    from nova import service
  File "/opt/stack/nova/nova/service.py", line 34, in <module>
    from nova import conductor
  File "/opt/stack/nova/nova/conductor/__init__.py", line 17, in <module>
    from nova.conductor import api as conductor_api
  File "/opt/stack/nova/nova/conductor/api.py", line 20, in <module>
    from nova.conductor import manager
  File "/opt/stack/nova/nova/conductor/manager.py", line 17, in <module>
    from nova.api.ec2 import ec2utils
  File "/opt/stack/nova/nova/api/ec2/__init__.py", line 31, in <module>
    from nova.api.ec2 import apirequest
  File "/opt/stack/nova/nova/api/ec2/apirequest.py", line 27, in <module>
    from nova.api.ec2 import ec2utils
  File "/opt/stack/nova/nova/api/ec2/ec2utils.py", line 22, in <module>
    from nova import availability_zones
  File "/opt/stack/nova/nova/availability_zones.py", line 20, in <module>
    from nova import db
  File "/opt/stack/nova/nova/db/__init__.py", line 23, in <module>
    from nova.db.api import *
  File "/opt/stack/nova/nova/db/api.py", line 48, in <module>
    from nova.cells import rpcapi as cells_rpcapi
  File "/opt/stack/nova/nova/cells/rpcapi.py", line 27, in <module>
    from nova import exception
  File "/opt/stack/nova/nova/exception.py", line 104, in <module>
    class NovaException(Exception):
  File "/opt/stack/nova/nova/exception.py", line 112, in NovaException
    message = _("An unknown exception occurred.")
NameError: name '_' is not defined