网址捕获的正则表达式（\\ w +）与某些网址不匹配

Question

The two lines of the urls.py config file for my_app are shown below. They're almost the same, only the second has a uuid4 appended to it

# preview views to allow us to preview stuff
url(r'^(?P<hash>\w+)/preview/$', Start.as_view(), {'preview':True}, name='preview'),
url(r'^(?P<hash>\w+)/preview/(?P<uuid>[a-f0-9]{8}-?[a-f0-9]{4}-?4[a-f0-9]{3}-?[89ab][a-f0-9]{3}-?[a-f0-9]{12})/$', PreviewController.as_view(), name='previewcontroller'),

The following urls work without error:

• http://example.com/my_app/2307099758/preview/
• http://example.com/my_app/2660962971/preview/
• http://example.com/my_app/475966143/preview/

The following urls yield the below error (all hash values are valid, but that shouldn't affect the url resolution):

• http://example.com/my_app/841211121/preview/
• http://example.com/my_app/2398929036/preview/

Internal Server Error: /my_app/841211121/preview/

NoReverseMatch at /my_app/841211121/preview/ Reverse for 'previewcontroller' with arguments '()' and keyword arguments '{'uuid': None, 'hash': '841211121'}' not found. 1 pattern(s) tried: ['my_app/(?P\\w+)/preview/(?P[a-f0-9]{8}-?[a-f0-9]{4}-?4[a-f0-9]{3}-?[89ab][a-f0-9]{3}-?[a-f0-9]{12})/$']

Request Method: GET Request URL: http://example.com/my_app/841211121/preview/ Django Version: 1.10...

Regex101.com says that the url should match (with escaped slashes, of course). Why on earth are the second group of urls not matching the preview url, and what is provoking the url resolver to attempt to match them to previewcontroller when there is no uuid string appended to the url?

Answer 1

Django is correctly resolving the /my_app/841211121/preview/ and running the correct view.

The problem is occurring when Django runs the Start view. It looks like a reverse() call or {% url %} template tag is failing.