`threading.Thread`'s group parameter is a nuisance

For some background: on DPO, someone suggested a threading.run function. I was in favor of the idea on the basis that threading.Thread has a clunky constructor. That aside, I think we can try to improve it.

In particular, the group parameter is an annoying sharp edge. It's the first positional argument, so threading.Thread(my_function) doesn't work, and instead you get a cryptic error message saying group argument must be None for now. I've fallen victim to this many times.

The docs say that group is reserved for a future ThreadGroup class:

group must be None as it is reserved for future extension when a ThreadGroup class is implemented.

I did some digging, and it seems it was proposed to add a ThreadGroup back in 2014: #66212. Many were not in favor of the idea, as it looked like a worse version of ThreadPoolExecutor. Other than the existence of this parameter, I can't see much reason to ever add a ThreadGroup. So, what do we do about group?

I think it's feasible to deprecate and remove it entirely. We can do this by changing the default group parameter to a private sentinel value, and then if a user passes anything to it (including None), we emit a deprecation warning. In five years, we remove the parameter, making target the first positional parameter and thus allowing Thread(my_function) to work.

Most people use the threading.Thread(target=...) pattern for creating threads, and they won't be broken by a deprecation or a removal. For the people who do use the Thread(None, function) pattern, migrating is fairly trivial.

What do others think? Would a removal result in too much breakage?

Bắt đầu với hàm khởi tạo threading.Thread và tài liệu liên kết với nó, sau đó xem xét issue #66212 và cuộc thảo luận DPO được liên kết để tìm hiểu các mối lo ngại thiết kế trước đây. Xác định hành vi về khả năng tương thích, cảnh báo và di chuyển đối với các cách sử dụng đối số vị trí hiện có; công việc được xem là hoàn tất khi đạt được sự thống nhất về việc có nên ngừng sử dụng tham số group hay không và nếu có thì sẽ loại bỏ tham số này như thế nào.