Unsubscribe from a mailing list that implements the one-click List-Unsubscribe RFC 8058, in Python with no external libraries. Takes raw email text as stdin.

unsubscribe.py

'''
automatically trigger a one-click unsubscribe
in an email, according to RFC 8058
'''
from email.header import make_header, decode_header
from email.parser import HeaderParser
import sys
import re
import urllib.request

text = sys.stdin.read()
post = 'List-Unsubscribe=One-Click'

z = HeaderParser().parsestr(text)
if z["List-Unsubscribe-Post"] != post:
    print("Does not support (RFC 8058)", file=sys.stderr)
    sys.exit(1)
data = str(make_header(decode_header(z["List-Unsubscribe"])))
url = re.search("<(https://.+?)>", data).group(1)
print(url, file=sys.stderr)
with urllib.request.urlopen(url, data=post.encode('ascii')) as f:
    print(f.read().decode('utf-8'))