[Django] #31961: forms.ChoiceField calls choices callback multiple times.
Django
--------------------------------------+------------------------
Reporter: Roy Smith | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
--------------------------------------+------------------------
I'm running:
Python 3.7
Django 2.2
Debian 4.9
If I configure a forms ChoiceField with a callback function for choices,
it gets called twice each time I render the form:
{{{
from unittest import TestCase
from django import forms
def callback():
print("callback")
return [('foo', 'bar')]
class MyForm(forms.Form):
f = forms.ChoiceField(choices=callback)
class FormTest(TestCase):
MyForm().as_p()
}}}
prints:
{{{
./manage.py test spi.test_f
callback
callback
System check identified no issues (0 silenced).
----------------------------------------------------------------------
Ran 0 tests in 0.000s
OK
}}}
This is the same sort of problem described in #26665 and/or #11390. It's
an obvious performance issue, but more than that, if can beak behavior if
the callback is non-idempotent.
I discovered this because I had patched my callback using unttest.mock to
return a sequence of return values and got hard-to-diagnose test failures.
Specifically, my test failed because it raised StopIteration when it ran
out of values to return.
--
Ticket URL: <https://code.djangoproject.com/ticket/31961>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Reporter: Roy Smith | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.2
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Description changed by Roy Smith:
Old description:
New description:
I'm running:
Python 3.7
Django 2.2
Debian 4.9
If I configure a forms ChoiceField with a callback function for choices,
it gets called twice each time I render the form:
{{{
from unittest import TestCase
from django import forms
def callback():
print("callback")
return [('foo', 'bar')]
class MyForm(forms.Form):
f = forms.ChoiceField(choices=callback)
class FormTest(TestCase):
MyForm().as_p()
}}}
prints:
{{{
./manage.py test spi.test_f
callback
callback
System check identified no issues (0 silenced).
----------------------------------------------------------------------
Ran 0 tests in 0.000s
OK
}}}
This is the same sort of problem described in #26665 and/or #11390. It's
an obvious performance issue, but more than that, it can beak behavior if
the callback is non-idempotent.
I discovered this because I had patched my callback using unttest.mock to
return a sequence of return values and got hard-to-diagnose test failures.
Specifically, my test failed because it raised StopIteration when it ran
out of values to return.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/31961#comment:1>
Django
Reporter: Roy Smith | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.2
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Comment (by Roy Smith):
fixed typo
--
Ticket URL: <https://code.djangoproject.com/ticket/31961#comment:2>
Django
Reporter: Roy Smith | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.2
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Comment (by Carlton Gibson):
Hi Roy.
Thanks for the report. Short of a concrete suggestion here, I’m struggling
to see how this isn’t just a duplicate of #11390.
[https://code.djangoproject.com/ticket/11390#comment:16 The conclusion
there seems unchanged]:
> ...I'm not sure how or if it's possible to combine the two remaining
calls...
> One's the in memory model being instantiated and the other's the
ModelForm field/widget populating it's values. They seem separate and I'm
not sure where any memoisation of this value would go or if it would be a
great idea.
Russel’s initial reply seems the appropriate workaround.
What would be your thought there?
--
Ticket URL: <https://code.djangoproject.com/ticket/31961#comment:3>
Django
Reporter: Roy Smith | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.2
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Comment (by Roy Smith):
I'm not familiar with the django code internals, so I can't make any
concrete suggestions about how to fix it. At the very least, however, it
should be documented.
--
Ticket URL: <https://code.djangoproject.com/ticket/31961#comment:4>
Django
Reporter: Roy Smith | Owner: nobody
Component: Forms | Version: 2.2
Severity: Normal | Resolution: duplicate
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Changes (by Carlton Gibson):
* status: new => closed
* resolution: => duplicate
Comment:
Let's close as a duplicate of #11390.
The `ChoiceField` docs already mention the evaluation during the form
initialization. I've [https://github.com/django/django/pull/13376 opened a
PR with a possible clarification].
--
Ticket URL: <https://code.djangoproject.com/ticket/31961#comment:5>