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Opened 3 years ago

Closed 3 years ago

#15127 closed Bug (fixed)

form.fields is still tied to class variables

Reported by: absoludity Owned by: nobody
Component: Forms Version: master
Severity: Normal Keywords:
Cc: wil@… Triage Stage: Ready for checkin
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description (last modified by kmtracey)

From django.forms.forms.BaseForm.__init__, it seems the intention is that a form's self.fields should be safe to update

        # The base_fields class attribute is the *class-wide* definition of
        # fields. Because a particular *instance* of the class might want to
        # alter self.fields, we create self.fields here by copying base_fields.
        # Instances should always modify self.fields; they should not modify
        # self.base_fields.
        self.fields = deepcopy(self.base_fields)

Yet

In [1]: from django import forms


In [5]: class MyForm(forms.Form):
    title = forms.ChoiceField(choices=(('mr', 'Mr.'), ('mrs', 'Mrs.')))
   ...:     def __init__(self, *args, **kwargs):
   ...:         super(MyForm, self).__init__(*args, **kwargs)
   ...:         self.fields['title'].choices += [('you', 'who')]
   ...: 

In [7]: f1 = MyForm()

In [8]: f1.fields['title'].choices
Out[8]: [('mr', 'Mr.'), ('mrs', 'Mrs.'), ('you', 'who')]

In [9]: f2 = MyForm()

In [10]: f2.fields['title'].choices
Out[10]: [('mr', 'Mr.'), ('mrs', 'Mrs.'), ('you', 'who'), ('you', 'who')]

In [11]: f3 = MyForm()

In [12]: f3.fields['title'].choices
Out[12]: 
[('mr', 'Mr.'),
 ('mrs', 'Mrs.'),
 ('you', 'who'),
 ('you', 'who'),
 ('you', 'who')]

In [17]: f3.base_fields['title']
Out[17]: <django.forms.fields.ChoiceField object at 0x26cc910>

In [18]: f3.fields['title']
Out[18]: <django.forms.fields.ChoiceField object at 0x26ccb10>

In [19]: f3.base_fields['title'].choices
Out[19]: 
[('mr', 'Mr.'),
 ('mrs', 'Mrs.'),
 ('you', 'who'),
 ('you', 'who'),
 ('you', 'who')]

So it seems that the instance field is definitely a deep copy, but the attributes of are not. A friend then pointed out Field.__deepcopy__:

http://code.djangoproject.com/browser/django/trunk/django/forms/fields.py#L193

which explains why the attributes are shared, but not whether this affect is intentional.

Attachments (2)

choicefield-deepcopy-v1.diff (2.0 KB) - added by dready 3 years ago.
deepcopy ChoiceField._choices with regression test
15127-form-field-choices-deepcopy.diff (2.5 KB) - added by julien 3 years ago.

Download all attachments as: .zip

Change History (9)

comment:1 Changed 3 years ago by kmtracey

  • Description modified (diff)
  • Needs documentation unset
  • Needs tests unset
  • Patch needs improvement unset

comment:2 Changed 3 years ago by russellm

  • Triage Stage changed from Unreviewed to Accepted

comment:3 Changed 3 years ago by lrekucki

  • Severity set to Normal
  • Type set to Bug

Changed 3 years ago by dready

deepcopy ChoiceField._choices with regression test

comment:4 Changed 3 years ago by dready

  • Cc wil@… added
  • Easy pickings unset
  • Has patch set
  • UI/UX unset

Could someone review the patch I just attached?

Changed 3 years ago by julien

comment:5 Changed 3 years ago by julien

  • Triage Stage changed from Accepted to Ready for checkin

The patch looks good, thanks! I've just made the tests slightly more explicit ;)

comment:6 Changed 3 years ago by dready

nice, thanks for that :)

comment:7 Changed 3 years ago by jezdez

  • Resolution set to fixed
  • Status changed from new to closed

In [16416]:

Fixed #15127 -- Properly copy the choices of choice fields. Thanks, dready and Julian Phalip.

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