Same algorithm as Sandcastle (https://github.com/0xSearches/sandcastle), but less clunky (and with annoying status messages). Also keeps flushing messages.

sandcastle.py

#!/usr/bin/env python3
import requests as rq
import sys

if len(sys.argv) < 3:
    print("Usage: python sandcastle.py companyname wordlist.txt", flush=True)
    exit()

company = sys.argv[1]
wordlist_dir = sys.argv[2]

with open(wordlist_dir, 'r') as f:
        wordlist = f.read().split("\n")

print(f"Attempting {len(wordlist)} combinations.", flush=True)

for index, attempt in enumerate(wordlist):
    r = rq.head(f"http://{company}{attempt}.s3.amazonaws.com")
    if r.status_code != 404:
        print(f"success: {company}{attempt} ({r.status_code})", flush=True)
    elif index % 25 == 0:
        print(f"status: {index}", flush=True)