#15127: form.fields is still tied to class variables
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Reporter: absoludity | Owner: nobody
Status: new | Milestone:
Component: Forms | Version: SVN
Keywords: | Stage: Unreviewed
Has_patch: 0 |
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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.
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Ticket URL: <http://code.djangoproject.com/ticket/15127>
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