Suffix in pathlib is not behaving like a file extension

Bug report

Bug description:

According to the docs here a suffix is defined as:

The file extension of the final component, if any

But pathlib doesn't behave as expected, illustrating that on Python 3.12.4:

>>> Path("Mr. Smith resume for review").suffix
'. Smith resume for review'

This is particularly problematic for methods like with_suffix. According to the docs here that should:

Return a new path with the suffix changed. If the original path doesn’t have a suffix, the new suffix is appended instead. If the suffix is an empty string, the original suffix is removed

But as established above, that results in:

>>> Path("Mr. Smith resume for review").with_suffix(".pdf")
PosixPath('Mr.pdf')

I've characterized that as a bug as that is not working as described, but could also be a matter of documentation improvement.

I see a few ways:

1. Implement add_suffix, or an argument to with_suffix, but I know that has been discussed before and was ultimately decided against. Also this is a matter of how suffix is defined, not how it's processed.
2. Sanity check what a suffix can be, e.g. suffix can't have white space. But ultimately difficult without making assumption.
3. Adjust the documentation: Clarify that suffix is not equal to file extension but something like last segment separated by a dot or similar. Maybe even with a warning that this can have unexpected behavior as showcased above.

CPython versions tested on:

3.12

Operating systems tested on:

Linux, Windows

Bắt đầu bằng cách tái hiện các ví dụ Python 3.12 cho pathlib về PurePath.suffix và with_suffix, sau đó kiểm tra phần triển khai và tài liệu của pathlib để xác định các hậu tố được định nghĩa như thế nào. So sánh hành vi quan sát được với cách diễn đạt trong tài liệu về phần mở rộng tệp và xác định xem vấn đề được giải quyết bằng cách thay đổi hành vi hay làm rõ tài liệu.