old_contents: #!/usr/bin/env python
  from __future__ import print_function
  
  from argparse import ArgumentParser
  from datetime import (
      datetime,
      timedelta,
      )
  import json
  import os
  import subprocess
  import sys
  
  
  def list_old_juju_containers(hours):
      env = dict(os.environ)
      containers = json.loads(subprocess.check_output([
          'lxc', 'list', '--format', 'json'], env=env))
      now = datetime.now()
      for container in containers:
          name = container['name']
          if not name.startswith('juju-'):
              continue
          # This produces local time.  lxc does not respect TZ=UTC.
          created_at = datetime.strptime(
              container['created_at'][:-6], '%Y-%m-%dT%H:%M:%S')
          age = now - created_at
          if age <= timedelta(hours=hours):
              continue
          yield name, age
  
  
  def main():
      parser = ArgumentParser('Delete old juju containers')
      parser.add_argument('--dry-run', action='store_true',
                          help='Do not actually delete.')
      parser.add_argument('--hours', type=int, default=1,
                          help='Number of hours a juju container may exist.')
      args = parser.parse_args()
      for container, age in list_old_juju_containers(args.hours):
          print('deleting {} ({} old)'.format(container, age))
          if args.dry_run:
              continue
          subprocess.check_call(('lxc', 'delete', '--verbose', '--force',
                                 container))
  
  
  if __name__ == '__main__':
      sys.exit(main())
  
new_contents: #!/usr/bin/env python
  from __future__ import print_function
  
  from argparse import ArgumentParser
  from datetime import (
      datetime,
      timedelta,
      )
  import json
  import os
  import subprocess
  import sys
  
  from dateutil import (
      parser as date_parser,
      tz,
      )
  
  
  def list_old_juju_containers(hours):
      env = dict(os.environ)
      containers = json.loads(subprocess.check_output([
          'lxc', 'list', '--format', 'json'], env=env))
      now = datetime.now(tz.gettz('UTC'))
      for container in containers:
          name = container['name']
          if not name.startswith('juju-'):
              continue
          created_at = date_parser.parse(container['created_at'])
          age = now - created_at
          if age <= timedelta(hours=hours):
              continue
          yield name, age
  
  
  def main():
      parser = ArgumentParser('Delete old juju containers')
      parser.add_argument('--dry-run', action='store_true',
                          help='Do not actually delete.')
      parser.add_argument('--hours', type=int, default=1,
                          help='Number of hours a juju container may exist.')
      args = parser.parse_args()
      for container, age in list_old_juju_containers(args.hours):
          print('deleting {} ({} old)'.format(container, age))
          if args.dry_run:
              continue
          subprocess.check_call(('lxc', 'delete', '--verbose', '--force',
                                 container))
  
  
  if __name__ == '__main__':
      sys.exit(main())
  
subject: Use dateutil to calculate age of container.