Python isdigit无法识别数字

Question

因此，在Python中，我使用.isdigit()检查它是否是一个数字，如果是，我将忽略它。但是，我的代码正在删除一行中的每个数字，除了第一个数字1。我已经做完了。它不仅仅是捕捉1。为什么会发生这种情况？为什么我的程序会删除除1之外的所有其他数字

下面是一个示例文件

1
00:00:09,068 --> 00:00:11,068
Ordinarily,
I'm a rule follower,

2
00:00:11,103 --> 00:00:12,369
But when someone tells me

3
00:00:12,404 --> 00:00:14,338
I can't bring my own snacks
into their stadium,

这就是结果。其中1不应包括在内

1
Ordinarily,
I'm a rule follower,
But when someone tells me
I can't bring my own snacks
into their stadium,

下面是我的代码

for line in lines:
    line = line.strip()
    if len(line.strip()) != 0 and line != 1 and line != "1":
        if (not line.isdigit()) and ('-->' not in line):
            line = del_brackets(line)
            line = ' '.join(''.join(' ' if ch in exclude else ch for ch in line).split())
            line = re.sub(r'\.\.\.', ' ', line)
            outfile.write(line.lstrip() + "\n")