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Python script returns error in AWS Lambda

Hi,

I'm currently working in AWS and trying to use a Lambda function to automate the creation of my AMIs. I'm doing this via the use of the Python script below, but when I test it it returns an error. Can anyone shed any light on what I should be looking at please?

Script:

import boto3
import collections
import datetime
import sys
import pprint

ec = boto3.client('ec2')
#image = ec.Image('id')

def lambda_handler(event, context):
   
    reservations = ec.describe_instances(
        Filters=[
            {'Name': 'tag-key', 'Values': ['backup', 'Backup']},
        ]
    ).get(
        'Reservations', []
    )

    instances = sum(
        [
            [i for i in r['Instances']]
            for r in reservations
        ], [])

    print "Found %d instances that need backing up" % len(instances)

    to_tag = collections.defaultdict(list)

for instance in instances:
    try:
        retention_days = [
            int(t.get('Value')) for t in instance['Tags']
            if t['Key'] == 'Retention'][0]
    except IndexError:
        retention_days = 7

    finally:

        #for dev in instance['BlockDeviceMappings']:
        #    if dev.get('Ebs', None) is None:
        #        continue
        #    vol_id = dev['Ebs']['VolumeId']
        #    print "Found EBS volume %s on instance %s" % (
        #        vol_id, instance['InstanceId'])

            #snap = ec.create_snapshot(
            #    VolumeId=vol_id,
            #)
           
            #create_image(instance_id, name, description=None, no_reboot=False, block_device_mapping=None, dry_run=False)
            # DryRun, InstanceId, Name, Description, NoReboot, BlockDeviceMappings
            create_time = datetime.datetime.now()
           create_fmt = create_time.strftime('%Y-%m-%d')
       
            AMIid = ec.create_image(InstanceId=instance['InstanceId'], Name="Lambda - " + instance['InstanceId'] + " from " + create_fmt, Description="Lambda created AMI of instance " + instance['InstanceId'] + " from " + create_fmt, NoReboot=True, DryRun=False)

           
            pprint.pprint(instance)
            #sys.exit()
            #break
       
            #to_tag[retention_days].append(AMIid)
           
            to_tag[retention_days].append(AMIid['ImageId'])
           
            print "Retaining AMI %s of instance %s for %d days" % (
                AMIid['ImageId'],
                instance['InstanceId'],
                retention_days,
            )

    print to_tag.keys()
   
    for retention_days in to_tag.keys():
        delete_date = datetime.date.today() + datetime.timedelta(days=retention_days)
        delete_fmt = delete_date.strftime('%m-%d-%Y')
        print "Will delete %d AMIs on %s" % (len(to_tag[retention_days]), delete_fmt)
       
        #break
   
        ec.create_tags(
            Resources=to_tag[retention_days],
            Tags=[
                {'Key': 'DeleteOn', 'Value': delete_fmt},
            ]
        )
import boto3
import collections
import datetime
import sys
import pprint

ec = boto3.client('ec2')
#image = ec.Image('id')

def lambda_handler(event, context):
   
    reservations = ec.describe_instances(
        Filters=[
            {'Name': 'tag-key', 'Values': ['backup', 'Backup']},
        ]
    ).get(
        'Reservations', []
    )

    instances = sum(
        [
            [i for i in r['Instances']]
            for r in reservations
        ], [])

    print "Found %d instances that need backing up" % len(instances)

    to_tag = collections.defaultdict(list)

for instance in instances:
    try:
        retention_days = [
            int(t.get('Value')) for t in instance['Tags']
            if t['Key'] == 'Retention'][0]
    except IndexError:
        retention_days = 7

    finally:

        #for dev in instance['BlockDeviceMappings']:
        #    if dev.get('Ebs', None) is None:
        #        continue
        #    vol_id = dev['Ebs']['VolumeId']
        #    print "Found EBS volume %s on instance %s" % (
        #        vol_id, instance['InstanceId'])

            #snap = ec.create_snapshot(
            #    VolumeId=vol_id,
            #)
           
            #create_image(instance_id, name, description=None, no_reboot=False, block_device_mapping=None, dry_run=False)
            # DryRun, InstanceId, Name, Description, NoReboot, BlockDeviceMappings
            create_time = datetime.datetime.now()
           create_fmt = create_time.strftime('%Y-%m-%d')
       
            AMIid = ec.create_image(InstanceId=instance['InstanceId'], Name="Lambda - " + instance['InstanceId'] + " from " + create_fmt, Description="Lambda created AMI of instance " + instance['InstanceId'] + " from " + create_fmt, NoReboot=True, DryRun=False)

           
            pprint.pprint(instance)
            #sys.exit()
            #break
       
            #to_tag[retention_days].append(AMIid)
           
            to_tag[retention_days].append(AMIid['ImageId'])
           
            print "Retaining AMI %s of instance %s for %d days" % (
                AMIid['ImageId'],
                instance['InstanceId'],
                retention_days,
            )

    print to_tag.keys()
   
    for retention_days in to_tag.keys():
        delete_date = datetime.date.today() + datetime.timedelta(days=retention_days)
        delete_fmt = delete_date.strftime('%m-%d-%Y')
        print "Will delete %d AMIs on %s" % (len(to_tag[retention_days]), delete_fmt)
       
        #break
   
        ec.create_tags(
            Resources=to_tag[retention_days],
            Tags=[
                {'Key': 'DeleteOn', 'Value': delete_fmt},
            ]
        )





The error returned:

START RequestId: 9e402ce9-cfeb-11e8-aea6-6da14ad56074 Version: $LATEST
module initialization error: name 'instances' is not defined

END RequestId: 9e402ce9-cfeb-11e8-aea6-6da14ad56074
REPORT RequestId: 9e402ce9-cfeb-11e8-aea6-6da14ad56074      Duration: 525.08 ms      Billed Duration: 600 ms       Memory Size: 128 MB      Max Memory Used: 56 MB      
module initialization error
name 'instances' is not defined

Many Thanks in advance!
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Indent all of your code starting from line 32 until the end.  from this line
for instance in instances:

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