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")