code: def lookup_instance(name: str, instance_type: str = '', image_name: str = '',
                      states: tuple = ('running', 'stopped', 'initializing')):
    
  
    ec2 = get_ec2_resource()
  
    instances = ec2.instances.filter(
      Filters=[{'Name': 'instance-state-name', 'Values': states}])
  
    prefix = get_prefix()
    username = get_username()
  
    # look for an existing instance matching job, ignore instances launched
    # by different user or under different resource name
    result = []
    for i in instances.all():
      instance_name = get_name(i)
      if instance_name != name:
        continue
  
      seen_prefix, seen_username = parse_key_name(i.key_name)
      if prefix != seen_prefix:
        print(f"Found {name} launched under {seen_prefix}, ignoring")
        continue
      if username != seen_username:
        print(f"Found {name} launched by {seen_username}, ignoring")
        continue
  
      if instance_type:
        assert i.instance_type == instance_type, f"Found existing instance for job {name} but different instance type ({i.instance_type}) than requested ({instance_type}), terminate {name} first or use new task name."
  
      if image_name:
        assert i.image.name == image_name, f"Found existing instance for job {name} but launched with different image ({i.image.name}) than requested ({image_name}), terminate {name} first or use new task name."
      result.append(i)
  
      assert len(result) < 2, f"Found two instances with name {name}"
      if not result:
        return None
      else:
        return result[0]
docs: Looks up AWS instance for given instance name, like
     simple.worker. If no instance found in current AWS environment, returns None.