python ttesting.py 
DEBUG:swh.lister.core.lister_base:Loading config from lister_gnu
INFO:swh.core.config:Loading config file /home/archit/.config/swh/lister_gnu.yml
DEBUG:swh.lister.core.lister_base:<swh.lister.gnu.lister.GNULister object at 0x7f526d50dac8> CONFIG={'content_size_limit': 104857600, 'log_db': 'dbname=softwareheritage-log', 'storage': {'cls': 'remote', 'args': {'url': 'http://localhost:5002/'}}, 'scheduler': {'cls': 'remote', 'args': {'url': 'http://localhost:5008/'}}, 'lister': {'cls': 'local', 'args': {'db': 'postgresql:///lister-gnu'}}, 'credentials': [], 'cache_responses': True, 'cache_dir': '/home/archit/.cache/swh/lister/gnu/'}
DEBUG:urllib3.connectionpool:Starting new HTTPS connection (1): ftp.gnu.org:443
DEBUG:urllib3.connectionpool:https://ftp.gnu.org:443 "GET /tree.json.gz HTTP/1.1" 200 568865
DEBUG:root:models: 381
DEBUG:urllib3.connectionpool:Starting new HTTP connection (1): localhost:5002
DEBUG:urllib3.connectionpool:http://localhost:5002 "POST /origin/add_multi HTTP/1.1" 200 20136
DEBUG:urllib3.connectionpool:Starting new HTTP connection (1): localhost:5008
DEBUG:urllib3.connectionpool:http://localhost:5008 "POST /create_tasks HTTP/1.1" 400 2193
Traceback (most recent call last):
  File "ttesting.py", line 5, in <module>
    gnu_lister()
  File "/home/archit/.virtualenvs/swh/lib/python3.6/site-packages/celery-4.3.0rc2-py3.6.egg/celery/local.py", line 191, in __call__
    return self._get_current_object()(*a, **kw)
  File "/home/archit/.virtualenvs/swh/lib/python3.6/site-packages/swh/scheduler/task.py", line 45, in __call__
    return super().__call__(*args, **kwargs)
  File "/home/archit/.virtualenvs/swh/lib/python3.6/site-packages/celery-4.3.0rc2-py3.6.egg/celery/app/task.py", line 390, in __call__
    return self.run(*args, **kwargs)
  File "/home/archit/swh-environment/swh-lister/swh/lister/gnu/tasks.py", line 12, in gnu_lister
    GNULister(**lister_args).run()
  File "/home/archit/swh-environment/swh-lister/swh/lister/core/simple_lister.py", line 74, in run
    response, injected_repos = self.ingest_data(dump_not_used_identifier)
  File "/home/archit/swh-environment/swh-lister/swh/lister/core/simple_lister.py", line 56, in ingest_data
    self.create_missing_origins_and_tasks(models, injected)
  File "/home/archit/swh-environment/swh-lister/swh/lister/core/lister_base.py", line 499, in create_missing_origins_and_tasks
    (task_dicts for (_, _, task_dicts) in tasks.values()))
  File "/home/archit/.virtualenvs/swh/lib/python3.6/site-packages/swh/scheduler/api/client.py", line 45, in create_tasks
    return self.post('create_tasks', {'tasks': tasks})
  File "/home/archit/swh-environment/swh-core/swh/core/api/__init__.py", line 198, in post
    return self._decode_response(response)
  File "/home/archit/swh-environment/swh-core/swh/core/api/__init__.py", line 230, in _decode_response
    raise pickle.loads(decode_response(response))
ModuleNotFoundError: No module named 'psycopg2.errors'