#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.