#17492 closed Bug (fixed)
url backreferencing can not be reversed.
| Reported by: | Nate Bragg | Owned by: | Nate Bragg |
|---|---|---|---|
| Component: | Core (Other) | Version: | 1.3 |
| Severity: | Normal | Keywords: | |
| Cc: | Triage Stage: | Unreviewed | |
| Has patch: | yes | Needs documentation: | no |
| Needs tests: | no | Patch needs improvement: | no |
| Easy pickings: | no | UI/UX: | no |
Description
If a url pattern uses backreferencing (i.e., "(?P=previously_named_group)"), the reversal fails, throwing up "Non-reversible reg-exp portion" ValueError. The problem occurs in django.utils.regex_helper.normalize which gives up on any character following a "(?P" other than "<".
Attachments (2)
Change History (9)
comment:1 by , 13 years ago
| Owner: | changed from to |
|---|---|
| Status: | new → assigned |
comment:3 by , 13 years ago
After being encouraged to on IRC - here's my rationale:
I had something like this in my urlpatterns:
url(r'^static_text/(?P<group_one>[a-z][a-z_]*)/(?P<group_two>\d+)/(?P=group_one)_(?P=group_two)_(?P<group_three>\w+)/$', views.a_view)
Because "(?P=" wasn't being parsed, it was choking on reversing... a DIFFERENT pattern. So, I figured the right thing to do would be to recognize this pattern too, since backreferences are so simple (i.e., they have to only have an identifier name between '=' and ')', and that identifier name had to previously have occurred).
Now, in my patch, I don't check that the backreference actually occurred! BUT - that's okay, because if your url pattern has that problem, it didn't compile anyhow, and you never got to 'reverse' anyhow (that, and I reasoned that this behavior is in line with other omissions that 'normalize' allows).
by , 13 years ago
| Attachment: | 17492.diff added |
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comment:4 by , 13 years ago
| Patch needs improvement: | set |
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I've added in a urlpatterns_reverse test, and it identifies a problem. See the commented test line in there:
Currently, reversing a named pattern still works with a list of arguments as well as a dictionary. Using a named backreference doesn't work with a list of arguments in the same way (you shouldn't have to provide the name twice).
Unless this can be resolved, I'm not quite sure that this can be added.
by , 13 years ago
| Attachment: | regex_backreference.diff added |
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A patch to regex_helper.py, along with unit tests for normalize.
comment:5 by , 13 years ago
| Patch needs improvement: | unset |
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Very good catch! Thankfully, it has a simple solution - None can be passed in as the variable, which excludes it. With my replacement patch, your test cases now both pass.
This patch resolves the error, allowing for named group backreferencing in url patterns.
It also includes unittests for regex_helper.normalize, testing most of its functionality (namely: empty pattern, escaped characters, ignored groups, non-capturing group, positional group, named group, and finally, backreferenced group, of course).