PEP 677: Runtime Behavior Specification

[stroxler]

I had forgotten to port the detailed spec from
https://docs.google.com/document/d/15nmTDA_39Lo-EULQQwdwYx_Q1IYX4dD5WPnHbFG71Lk/edit

(It was originally separate because I was concerned there might be too much debate and thrash to put it in the PEP, but that did not turn out to be true).

[stroxler]

Updates:

• Flatten the proposal somewhat:
  • Use an is_async flag so we only need one callable type
  • Use Ellipses to indicate AnyArguments
• Use python pseudocode where possible, English is neither concise nor specific enough
• Add a runtime section to rejected alternatives discussing other choices we could make
  • I'd be happy to put up a second PR flipping things if we prefer one of the alternatives

[gvanrossum]

I’m going to have to take a backseat for now, but one source of inspiration could be the ’inspect’ module.

[stroxler]

Updates:

• Switch to an inspect-like approach where arguments is either Ellipses or a tuple of thinks that know their "kind"
• Change even more of the discussion to use Python pseudocode rather than text
• Update the "Rejected Alternatives" section, including why we use "arguments" rather than "parameters"

[gvanrossum]

(Some of my more substantive comments can wait for the python-dev discussion if you prefer.)

[gvanrossum]

That makes for very long enum names. Although perhaps @global_enum could help?

[stroxler]

I didn't know @global_enum was a thing!

Should https://docs.python.org/3.11/library/enum.html say something about it?

I had to do a code search on CPython to confirm it exists, search engines appear to be unaware of it.

[stroxler]

Updates:

• Add some type annotations, remove others
• Adjust wording in a few places as suggested in code review
• Add missing get_parameters function to the backward-compatible API section

[gvanrossum]

(Rest looks good, just need to fix two declarations.)

[gvanrossum]

Okay, merging now.