#31070: Add a check for URLconfs that mix named and unnamed capture groups
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Reporter: Baptiste Mispelon | Owner: nobody
Type: New feature | Status: new
Component: Core (System checks) | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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When using `re_path()`, Django supports the following types of capture
groups:
1) Named: `(?P<year>\d+)/(?P<month>\d+)/`
2) Unnamed: `(\d+)/(?\d+)/`
3) Mixed: `(?P<year>\d+)/(\d+)/`
If you have a view with the following signature: `def view(request, *args,
**kwargs)` and a URL `/2019/11/`, then the view will be called with the
following arguments (respectively):
1) `args=(), kwargs={'year': '2019', 'month': '11'}`
2) `args=('2019', '11'), kwargs={}`
3) `args=(), kwargs={'year': '2019'}`
Case number 3 is a bit surprising but it's documented both in the
reference docs [1]:
When a match is made, captured groups from the regular expression are
passed to the view – as named arguments if the groups are named, and as
positional arguments otherwise.
and in the topics docs [2]:
When both styles are mixed, any unnamed groups are ignored and only
named groups are passed to the view function.
The topics doc actually discourages the use of unnamed capture group:
This usage isn’t particularly recommended as it makes it easier to
accidentally introduce errors between the intended meaning of a match and
the arguments of the view.
I propose introducing a new `urls.W009` check for the URLConfs that would
warn the user when they've configured a route that mixes both named and
unnamed capture groups. As a remedy, it would suggest converting the
unnamed groups to non-capturing groups (`(?:\d+)` syntax with our current
example).
[1] https://docs.djangoproject.com/en/dev/ref/urls/#re-path
[2] https://docs.djangoproject.com/en/dev/topics/http/urls/#using-unnamed-
regular-expression-groups
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Ticket URL: <https://code.djangoproject.com/ticket/31070>
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