Here's a really hack-y method of decoding multiple encoded Base64 strings. Useful for some very basic CTFs.
#!/usr/bin/env python3
import base64
from itertools import repeat
base64_string = input("Enter Base64 String: ")
decode_times = int(input("Enter number of times to decode: "))
for x in repeat(None, decode_times):
base64_string = base64.b64decode(base64_string)
print (base64_string)
Your mileage may vary.