what is reverse in Django

Question

When I read django code sometimes  I see in some templates reverse    I am not quite sure what this is but it is used together with HttpResponseRedirect  How and when is this reverse   supposed to be used   It would nice if someone gave an answer with some examples

User · Answer

The existing answers are quite clear  Just in case you do not know why it is called reverse  It takes an input of a url name and gives the actual url  which is reverse to having a url first and then give it a name

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reverse     Django documentation    Let s suppose that in your urls py you have defined this   url r  foo    some view  name  url name      In a template you can then refer to this url as    lt  -- django  lt   1 4 -- gt   lt a href     url url name     gt link which calls some view lt  a gt    lt  -- django  gt   1 5 or with    load url from future    in your template -- gt   lt a href     url  url name      gt link which calls some view lt  a gt    This will be rendered as    lt a href   foo   gt link which calls some view lt  a gt    Now say you want to do something similar in your views py - e g  you are handling some other url  not  foo   in some other view  not some view  and you want to redirect the user to  foo   often the case on successful form submission    You could just do   return HttpResponseRedirect   foo      But what if you want to change the url in future  You d have to update your urls py and all references to it in your code  This violates DRY  Don t Repeat Yourself   the whole idea of editing one place only  which is something to strive for   Instead  you can say   from django urls import reverse return HttpResponseRedirect reverse  url name      This looks through all urls defined in your project for the url defined with the name url name and returns the actual url  foo    This means that you refer to the url only by its name attribute - if you want to change the url itself or the view it refers to you can do this by editing one place only - urls py

User · Answer

The reverse   is used to adhere the django DRY principle i e if you change the url in future then you can reference that url using reverse urlname

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The function supports the dry principle - ensuring that you don t hard code urls throughout your app  A url should be defined in one place  and only one place - your url conf  After that you re really just referencing that info   Use reverse   to give you the url of a page  given either the path to the view  or the page name parameter from your url conf  You would use it in cases where it doesn t make sense to do it in the template with    url  my-page       There are lots of possible places you might use this functionality  One place I ve found I use it is when redirecting users in a view  often after the successful processing of a form -  return HttpResponseRedirect reverse  thanks-we-got-your-form-page     You might also use it when writing template tags   Another time I used reverse   was with model inheritance  I had a ListView on a parent model  but wanted to get from any one of those parent objects to the DetailView of it s associated child object  I attached a get  child url   function to the parent which identified the existence of a child and returned the url of it s DetailView using reverse

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Existing answers did a great job at explaining the what  of this reverse   function in Django    However  I d hoped that my answer shed a different light at the why  why use reverse   in place of other more straightforward  arguably more pythonic approaches in template-view binding  and what are some legitimate reasons for the popularity of this  redirect via reverse   pattern  in Django routing logic   One key benefit is the reverse construction of a url  as others have mentioned  Just like how you would use    url  profile  profile id    to generate the url from your app s url configuration file  e g  path   lt int profile id gt  profile   views profile  name  profile     But as the OP have noted  the use of reverse   is also commonly combined with the use of HttpResponseRedirect  But why      I am not quite sure what this is but it is used together with HttpResponseRedirect  How and when is this reverse   supposed to be used    Consider the following views py   from django http import HttpResponseRedirect from django urls import reverse  def vote request  question id       question   get object or 404 Question  pk question id      try          selected   question choice set get pk request POST  choice        except KeyError            handle exception         pass     else          selected votes    1         selected save           return HttpResponseRedirect reverse  polls polls-results                                       args  question id               And our minimal urls py   from django urls import path from   import views  app name    polls  urlpatterns         path   lt int question id gt  results    views results  name  polls-results        path   lt int question id gt  vote    views vote  name  polls-vote       In the vote   function  the code in our else block uses reverse along with HttpResponseRedirect in the following pattern   HttpResponseRedirect reverse  polls polls-results                                           args  question id    This first and foremost  means we don t have to hardcode the URL  consistent with the DRY principle  but more crucially  reverse   provides an elegant way to construct URL strings by handling values unpacked from the arguments  args  question id  is handled by URLConfig   Supposed question has an attribute id which contains the value 5  the URL constructed from the reverse   would then be     polls 5 results     In normal template-view binding code  we use HttpResponse   or render   as they typically involve less abstraction  one view function returning one template   def index request       return render request   polls index html      But in many legitimate cases of redirection  we typically care about constructing the URL from a list of parameters  These include cases such as    HTML form submission through POST request User login post-validation Reset password through JSON web tokens   Most of these involve some form of redirection  and a URL constructed through a set of parameters  Hope this adds to the already helpful thread of answers

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This is an old question  but here is something that might help someone     From the official docs      Django provides tools for performing URL reversing that match the   different layers where URLs are needed  In templates  Using the url   template tag  In Python code  Using the reverse   function  In higher   level code related to handling of URLs of Django model instances  The   get absolute url   method    Eg  in templates  url tag    lt a href     url  news-year-archive  2012     gt 2012 Archive lt  a gt    Eg  in python code  using the reverse function    return HttpResponseRedirect reverse  news-year-archive   args  year

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There is a doc for that  https   docs djangoproject com en dev topics http urls  reverse-resolution-of-urls  it can be used to generate an URL for a given view  main advantage is that you do not hard code routes in your code

[django] what is reverse() in Django

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