Thursday, February 27, 2014

Re: View function and URL Conf basic question

On Wednesday, February 26, 2014 9:24:51 AM UTC-4:30, Daniel Roseman wrote:
On Wednesday, 26 February 2014 08:10:40 UTC, ApathyBear wrote:
Here is my
from django.conf.urls.defaults import *  from mysite.views import hello, current_datetime, hours_ahead    urlpatterns = patterns('',      url(r'^hello/$', hello),      url(r'^time/$', current_datetime),      url(r'^time/plus/(\d{1,2})/$', hours_ahead),  )
And here is my View function associated with hours_ahead
from django.http import Http404, HttpResponse  import datetime    def hours_ahead(request, offset):      try:          offset = int(offset)      except ValueError:          raise Http404()      dt = + datetime.timedelta(hours=offset)      html = "<html><body>In %s hour(s), it will be %s.</body></html>" % (offset, dt)      return HttpResponse(html)
Now what is throwing me off is how 'offset' is a second argument to  the hours_ahead function. Yet I am not quite sure how it being the second argument makes it the case that it is associated with whatever is entered as a URL. Let me use an example to illustrate my confusion.

Say I request the URL: . Why is it the case that offset is '2'? I am not seeing why '2' is plucked out? What happened with 'time' and 'plus'? How does python/django know that the '2' is referring to offset?
That is what the regular expression does in your first snippet. `time` and `plus` are just matched, but not captured: the only thing that is captured is `(\d{1,2})`, because it is surrounded in parentheses.

If that's not clear for you, you should read a guide to regexes:  is a good one.

As Daniel points out, this is related to regular expressions. You can read a full explanation here:

You sholud also take a look at the 're' Python module. 


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