python替換一個文件里面的特定內容

f = open("1.txt", "r", encoding="utf-8")
f_new = open("2.txt", "w", encoding="utf-8")
find_str = "wangzai"
replace_str = "doubi"
for line in f:
    if find_str in line:
        line = line.replace(find_str, replace_str)
    f_new = write(line)
f.close()
f_new.close()
os.remove("config.txt")
os.rename("config1.txt", "config.txt")