Python写空白

I'm trying to make a program which would replace tags in a markdown file (.md) as follow : If it's an opening $ tag, replace it by \(, if it's a closing $ tag, replace it by \), copy every other characters.

不幸的是，当我尝试时，写入的文件确实很奇怪。有些行被复制，而其他行则没有。首先，我的每个测试文件的第一行和最后一行都没有被复制。中间的其他行也不太好。不同行上的相同文本不会同时复制。

这是我的程序：

import os

def conv1(path):
    """convert $$ tags to \( \)"""
    file = open(path, mode ='r') # open lesson with $ (.md)
    new = open(path + '.tmp', mode = 'w') # open blank file
    test = 0
    for lines in file:
        line = file.readline()
        i = 0
        length = len(line)
        while i < length:
            if line[i] == '$':
                if test % 2 == 0: # replace opening tag
                    line = line[:i] + '\(' + line [i + 1:]
                elif test % 2 == 1: # replace closing tag
                    line = line[:i] + '\)' + line [i + 1:]
                test +=1
                i += 2
                length += 1
            else :
                i += 1
        new.write(line + '\n')
    file.close()
    new.close()
    os.rename(str(path) + '.tmp', str(path))
    print('Done!')

您知道如何解决我的问题吗？

提前致谢

EloiLmr