newforms.Form.clean_data is not read-only

[jfindlay@…]

Is it possible to make newforms.Form.clean_data immutable? I'm kind of surprised it isn't, but I don't know the meaning or purpose of all things.

$ python manage.py shell
Python 2.4.4c1 (#2, Oct 11 2006, 21:51:02) 
[GCC 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from django import newforms
>>> class form(newforms.Form):
...   a = newforms.IntegerField()
...   b = newforms.CharField()
... 
>>> d = {'a': 1, 'b': 'field b'}
>>> f = form(d)
>>> f.is_valid()
True
>>> f.clean_data
{'a': 1, 'b': u'field b'}
>>> f.clean_data['a'] = 2
>>> f.clean_data
{'a': 2, 'b': u'field b'}

[anonymous]

Here's my example again, unwikified, or wikified depending on how you think.

$ python manage.py shell
Python 2.4.4c1 (#2, Oct 11 2006, 21:51:02) 
[GCC 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from django import newforms
>>> class form(newforms.Form):
...   a = newforms.IntegerField()
...   b = newforms.CharField()
... 
>>> d = {'a': 1, 'b': 'field b'}
>>> f = form(d)
>>> f.is_valid()
True
>>> f.clean_data
{'a': 1, 'b': u'field b'}
>>> f.clean_data['a'] = 2
>>> f.clean_data
{'a': 2, 'b': u'field b'}
>>> 

[Adrian Holovaty]

Hmm, I could go either way on this. Making clean_data an immutable dictionary would introduce a tiny bit of overhead, as we'd have to define our own ImmutableDict class. Do you really think having clean_data be mutable is a huge problem?

[anonymous]

I supposed that validated form data would have been treated in the same read-only manner as request.GET and request.POST and also considering the following paragraph from ​http://www.djangoproject.com/documentation/newforms/.

If you have a bound Form instance and want to change the data somehow, or if you want to bind an unbound Form instance to some data, create another Form instance. There is no way to change data in a Form instance. Once a Form instance has been created, you should consider its data immutable, whether it has data or not.

It seemed contradictory to me to have form data be considered immutable but then be able to modify it because the clean_data dict is not read-only.

[Adrian Holovaty]

(Fixed formatting in description.)

[Adrian Holovaty]

I implemented this in my local Django checkout but changed my mind at the last minute -- I don't see a good reason to make clean_data immutable, and I think it might be more of an annoyance than a protection. (And what would it protect from, anyway?)

For posterity, I've uploaded a patch of the changes I made, in case we change our minds in the future.

[Adrian Holovaty]

Implementation of immutable clean_dict

[Adrian Holovaty]

Note that the 3376_immutable_clean_dict.diff has a small problem -- it mistakenly removes the render_value unit tests.