from pathlib import Path
path=Path('/etc/caddy/Caddyfile')
s=path.read_text()
old='''reverse_proxy http://127.0.0.1:8090 http://103.114.163.226:48090 {\n\t\t\tlb_policy weighted_round_robin 10 4 4'''
new='''reverse_proxy http://127.0.0.1:8090 http://103.114.163.226:48090 {\n\t\t\tlb_policy weighted_round_robin 10 4'''
if old not in s:
    raise SystemExit('target weighted upstream block not found')
path.write_text(s.replace(old,new,1))