block-followers.py

import os, argparse, twitter

parser = argparse.ArgumentParser()
parser.add_argument('screen_name')
args = parser.parse_args()

api = twitter.Api(  # oauth credentials
    os.environ['CONSUMER_KEY'], os.environ['CONSUMER_SECRET'],
    os.environ['ACCESS_TOKEN_KEY'], os.environ['ACCESS_TOKEN_SECRET'],
    sleep_on_rate_limit=True  # just pause execution
)

cursor = -1
while cursor:
    next, prev, data = api.GetFollowerIDsPaged(  # Fetch page of followers
        screen_name=args.screen_name, cursor=cursor
    )
    cursor = next
    for user_id in data:
        result = api.CreateBlock(user_id=user_id)  # Send block request
        print(f"Blocked {result.name} (@{result.screen_name})")

This snippet relies on this library for the Twitter stuff: https://python-twitter.readthedocs.io/en/latest/