django – why is the request.POST object immutable?

by

It’s a bit of a mystery, isn’t it? Several superficially plausible theories turn out to be wrong on investigation:

  1. So that the POST object doesn’t have to implement mutation methods? No: the POST object belongs to the django.http.QueryDict class, which implements a full set of mutation methods including __setitem__, __delitem__, pop and clear. It implements immutability by checking a flag when you call one of the mutation methods. And when you call the copy method you get another QueryDict instance with the mutable flag turned on.

  2. For performance improvement? No: the QueryDict class gains no performance benefit when the mutable flag is turned off.

  3. So that the POST object can be used as a dictionary key? No: QueryDict objects are not hashable.

  4. So that the POST data can be built lazily (without committing to read the whole response), as claimed here? I see no evidence of this in the code: as far as I can tell, the whole of the response is always read, either directly, or via MultiPartParser for multipart responses.

  5. To protect you against programming errors? I’ve seen this claimed, but I’ve never seen a good explanation of what these errors are, and how immutability protects you against them.

In any case, POST is not always immutable: when the response is multipart, then POST is mutable. This seems to put the kibosh on most theories you might think of. (Unless this behaviour is an oversight.)

In summary, I can see no clear rationale in Django for the POST object to be immutable for non-multipart requests.

More Related Contents:

  1. 405 POST method not allowed
  2. Exception: You cannot access body after reading from request’s data stream
  3. How to upload a file in Django? [closed]
  4. How do I do an OR filter in a Django query?
  5. Django rest framework, use different serializers in the same ModelViewSet
  6. Setting the selected value on a Django forms.ChoiceField
  7. Load a Django template tag library for all views by default
  8. Output Django queryset as JSON
  9. Prevent Django SQLite db from being overwritten while pushing to Heroku
  10. Django: How can I call a view function from template?
  11. How to Unit test with different settings in Django?
  12. Django m2m form save ” through ” table
  13. How to get Django and ReactJS to work together?
  14. Django – how to specify a database for a model?
  15. How to reset migrations in Django 1.7
  16. “Post Image data using POSTMAN”
  17. Django model: delete() not triggered
  18. Django 1.8: Create initial migrations for existing schema
  19. Heroku app database resetting
  20. django @login_required decorator for a superuser
  21. What is the right way to validate if an object exists in a django view without returning 404?
  22. Authorization Credentials Stripped — django, elastic beanstalk, oauth
  23. How to use if/else condition on Django Templates?
  24. Django Order By Date, but have “None” at end?
  25. Django query case-insensitive list match
  26. How to limit file types on file uploads for ModelForms with FileFields?
  27. Django: access the parent instance from the Inline model admin
  28. Django/DRF – 405 Method not allowed on DELETE operation
  29. django : Serving static files through nginx
  30. Django: Using F arguments in datetime.timedelta inside a query

Leave a Comment