Update design FAQ 'switch' entry mention of `match-case`.

[dascritch]

Documentation

Describe the bug
I did a search to remember what was the switch keyword in Python, and the very first link I got is a not up-to-date page from Python 3.11 documentation, explaining that elif is great.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://docs.python.org/3.12/faq/design.html
2. Click on Why isn’t there a switch or case statement in Python?
3. match case isn't cited, but the catastrophic elif cascade is still the “reference”

Expected behavior
Correct it and explain why match case is a really better coding practice instead of cascaded elif (unreadable, unmaintainable, confuse)

Sidenote :
Found here what I was looking at.

Even on this not related page the author use return, and didn't think to replace elif with simplier if !

Linked PRs

• gh-111307 Updating match..case in design documentation #111312
• gh-111307: Update design FAQ 'switch' entry #115899
• [3.12] gh-111307: Update design FAQ 'switch' entry (GH-115899) #116703
• [3.11] gh-111307: Update design FAQ 'switch' entry (GH-115899) #116704

[hugovk]

Sounds like a good idea to recommend match at https://docs.python.org/3/faq/design.html?highlight=switch#why-isn-t-there-a-switch-or-case-statement-in-python, mentioning it's new in 3.10.

Would you like to propose something in a PR?

[dascritch]

I suppose it is in https://github.com/python/cpython/blob/main/Doc/faq/design.rst ? I try

[mdboom]

Cc @brandtbucher

[terryjreedy]

The diatribe against if-elif-else is wrong-headed. Match-case statements are executed as if case matches, do action, elif next case matches, do action, .... else _, do last action. People must understand this to read and write such properly. If-else is better for value range matching, which is quite common, since one otherwise has to add an if-clause to case statements anyway.

I write if-elif-else with return rather than if-if-if return since it is clearer at a glance that case-analysis is being done and exactly one condition will match and one suite executed. In simple cases, such can be reduced to return true_val if condition else false_val.

[terryjreedy]

The existing doc, at the time of the PR, does not say the 'elif is great'. I does say that that one "can do this easily enough", which I consider true. Contrary to "match case isn't cited", the entry says in the 2nd sentence, "For literal values, or constants within a namespace, you can also use a match ... case statement." So I do not see any urgent need for revision, but I do see room for improvement. PR #115899 mentions match-case first as Python's new switch-case statement and de-emphasizes if-else.