how to translate indent title to numbering title in python code

I have a table of content in the form of indent to keep relation like:

- title1
-- title1-1
-- title1-2
--- title1-2-1
--- title1-2-2
- title2
-- title2-1
-- title2-2
- title3
- title4

What I want to is to translate then into form of numbering format like:

1 title1
1.1 title1-1
1.2 title1-2
1.2.1 title1-2-1
1.2.2 title1-2-2
2 title2
2.1title2-1
2.2 title2-2
3 title3
4 title4

I have tried myself, but mostly they were transferred into desired format, but some could not, anyone can provide the perfect code, thanks advanced!

>Solution :

You could use the replacer callback of re.sub to implement the logic. In that callback use a stack (that is maintained across multiple replacements) to track the chapter numbers of upper "levels".

Code:

import re

def add_numbers(s):
    stack = [0]
    
    def replacer(s):
        indent = len(s.group(0)) - 1
        del stack[indent+1:]
        if indent >= len(stack):
            stack.append(0)
        stack[indent] += 1
        return ".".join(map(str,stack))
        

    return re.sub(r"^-+", replacer, s, flags=re.M)

Here is how you would call it on your example:

message_string = """- title1
-- title1-1
-- title1-2
--- title1-2-1
--- title1-2-2
- title2
-- title2-1
-- title2-2
- title3
- title4"""

res = add_numbers(message_string)
print(res)

This prints:

1 title1
1.1 title1-1
1.2 title1-2
1.2.1 title1-2-1
1.2.2 title1-2-2
2 title2
2.1 title2-1
2.2 title2-2
3 title3
4 title4