Improve syntax error for mixing keyword/positional in max patterns

[pablogsal]

BPO	44456
Nosy	@pablogsal, @miss-islington, @brandtbucher
PRs	bpo-44456: Improve the syntax error when mixing keyword and positional patterns #26793 [3.10] bpo-44456: Improve the syntax error when mixing keyword and positional patterns (GH-26793) #26900

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2021-06-24.15:36:01.476>
created_at = <Date 2021-06-18.21:07:47.426>
labels = []
title = 'Improve syntax error for mixing keyword/positional in max patterns'
updated_at = <Date 2021-06-24.15:36:05.975>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2021-06-24.15:36:05.975>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2021-06-24.15:36:01.476>
closer = 'pablogsal'
components = []
creation = <Date 2021-06-18.21:07:47.426>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 44456
keywords = ['patch']
message_count = 6.0
messages = ['396088', '396090', '396091', '396100', '396493', '396495']
nosy_count = 3.0
nosy_names = ['pablogsal', 'miss-islington', 'brandtbucher']
pr_nums = ['26793', '26900']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue44456'
versions = []

[pablogsal]

This got me confused for a sec when doing some live demo:

>>> match x:
...    case A(y=1, foo):
  File "<stdin>", line 2
    case A(y=1, foo):
                   ^
SyntaxError: invalid syntax

I propose to improve this to:

>>> match x:
...    case A(y=1, foo):
  File "<stdin>", line 2
    case A(y=1, foo):
                ^^^
SyntaxError: cannot mix keyword patterns and positional patterns

[pablogsal]

Btw, I noticed this is allowed:

>>> match x:
...    case A(foo, t=3):
...        ...
...

but this is not:

>>> match x:
...    case A(foo=3, t):

Is that on pourpose?

[pablogsal]

If this is supposed to mirror function calls, maybe the error should be::

>>> match a:
...    case A(foo=3, t):
  File "<stdin>", line 2
    case A(foo=3, t):
                  ^
SyntaxError: positional patterns follow keyword patterns

[brandtbucher]

Yep, it's intentional.

And yep, I like the new error message better. :)

[pablogsal]

New changeset 0acc258 by Pablo Galindo in branch 'main':
bpo-44456: Improve the syntax error when mixing keyword and positional patterns (GH-26793)
0acc258

[miss-islington]

New changeset 11f1a30 by Miss Islington (bot) in branch '3.10':
bpo-44456: Improve the syntax error when mixing keyword and positional patterns (GH-26793)
11f1a30