id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34148	Removing a field from form.fields previously added to _bound_fields_cache has no effect	Jan Pieter Waagmeester	Francesco Panico	"The fix for issue ""`BaseForm.__getitem__()` does unneeded work in the happy path"" (#32901) added to main in https://github.com/django/django/commit/edde2a069929c93e37835dc3f7c9a229040058e2, A shortcut was added to retrieve bound fields from `form._bound_fields_cache`.

If a form removes a field after the cache entry for that field was created, the field can be still retrieved from the cache, even though the field is not in `form.fields` anymore:

{{{
import django
from django import forms
from django.test import SimpleTestCase

class Form(forms.Form):
    action = forms.CharField()

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        # The form was iterated (in my case, separating basic and advanced fields)
        [field for field in self if getattr(field, 'advanced', False)]

        # After that, we remove a field (i.e. because it is not relevant for admins)
        del self.fields[""action""]


class FormTestCase(SimpleTestCase):
    def test_form(self):
        """"""
        The field should be removed from the instance,
        but it can be still retrieved from self._bound_fields_cache.
        """"""
        print(""django version"", django.VERSION)
        form = Form()

        with self.assertRaises(KeyError):
            form[""action""]
}}}

This succeeds with `django==3.2`:



{{{
pip install django==3.2.16
...
./manage.py test tests
System check identified no issues (0 silenced).
django version (3, 2, 16, 'final', 0)
.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK
}}}



But fails with `django==4.0.8` (and `django==4.1.3`):

{{{
pip install django==4.0.8
...
./manage test tests
Found 1 test(s).
System check identified no issues (0 silenced).
django version (4, 0, 8, 'final', 0)
F
======================================================================
FAIL: test_form (test_forms.FormTestCase)
The field should be removed from the instance,
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/Users/jieter/workspace/django-test/tests/test_forms.py"", line 27, in test_form
    form[""action""]
AssertionError: KeyError not raised

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)
}}}

"	Bug	closed	Forms	4.0	Normal	fixed		Chris Jerdonek	Ready for checkin	1	0	0	0	0	0