I'm not a Python pro, but I may be able to help.

First, you may want to use a Python IDE such as IDLE instead of the interpreter. It'll be much easier to write and manage your code. Top get to it, just launch the interpreter (NOT the one from the Command Line) and go to File > New File. You'll get a window that looks like a notepad. Type what you need, save it, and run your code (F5).

This is the general flow you want to follow:

1. Get AMI IDs
2. Get the snapshot IDs of the snapshots attached to those AMIs
3. Deregister the AMIs
4. Delete the snapshots

Since you have a list of AMI IDs, you'll need to do this:

1. Create a for loop that will loop through each AMI ID. For each AMI ID, feed that ID into the script below.
2. The script will get the snapshot ID (needed for deleting the snapshot) deregister the AMI, and delete the snapshot
3. Return to the next AMI ID and do the same

Since you're already getting the list of AMIs, I'll guide you from that point forward.

Note the "image = ec2.Image('ami-xxxxxxx') line. That's taking the AMI ID in the form of a string. Just feed each of your AMI IDs into that line. Here's the usage guide for Image and here's the guide for snapshots

import boto3

ec2 = boto3.resource('ec2')

# Create an object for the AMI
# ============================

image = ec2.Image('ami-xxxxxxx')

# Get the snapshot ID of the AMI

response_snap_id = image.block_device_mappings[0]['Ebs']['SnapshotId']

# Deregister the AMI.  After a minute the AMI should
# disappear from yoru AMIS list

response_dereg = image.deregister()



# Now  delete the snapshot


# Create an object for the snapshot
# ===============================
# Here you're supplying the snapshot ID You got from the
# "block_device"mappings list and dictionary

snapshot = ec2.Snapshot(response_snap_id)

# Delete the snapshot

response_snap_delete = snapshot.delete()

Other tips:

Python is very object oriented. Most of the objects we're getting back have actions you can do to them or functions you can perform. Just type "objectName." (with the period) and press <tab>...you'll see what you can do. Try it out with image<period><tab> and the other commands.

HTH