Resolver Attributes Error

[arasuthiru]

i getting attributes error.
custom resolver:
ami_finder.py

import abc
import logging

from botocore.exceptions import ClientError
from sceptre.resolvers import Resolver
from sceptre.exceptions import DependencyStackMissingOutputError
from sceptre.exceptions import StackDoesNotExistError

class AmiFinder(Resolver):
"""
Resolver for the configuration in a file.
:param argument: Configuration value to be returned.
:type argument: str
"""

def __init__(self, *args, **kwargs):
    super(AmiFinder, self).__init__(*args, **kwargs)
    self.logger = logging.getLogger(__name__)

def resolve(self):
    self.logger.info(self.argument)
    owner, ami_name = self.argument.split(':')
    try:
        r = self.connection_manager.call(
            service="ec2",
            command="describe_images",
            kwargs={"Owners": [owner], "Filters": [
                {'Name': 'name', 'Values': [ami_name]}]}
        )
    except ClientError as e:
        raise e

    sorted_amazon_amis = sorted(
        r['Images'], key=lambda x: x['CreationDate'])
    return str(sorted_amazon_amis[-1]['ImageId'])

setup.py
from setuptools import setup

setup(
name='ami_finder',
py_modules=['ami_finder'],
entry_points={
'sceptre.resolvers': [
'ami_finder = ami_finder:AmiFinder',
],
}
)

Stack config:

template_path: bastion.j2

parameters:
ImageId: !ami_finder 137112412989:amzn2-ami-hvm-*-x86_64-gp2
KeyName: "thiru-stage-key"
ParamEnv: thiru-stage
SubnetId: !stack_output stage/vpc.yaml::DMZSubnetA
VpcId: !stack_output stage/vpc.yaml::Vpc

sceptre_user_data:
Whitelist:
- 88.217.255.228/32

Stack outputs:

File "/home/thiru/.local/lib/python3.6/site-packages/ami_finder.py", line 28, in resolve
r = self.connection_manager.call(
AttributeError: 'AmiFinder' object has no attribute 'connection_manager'