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
3300	newforms Select widget only renders choices once when using generator	m_fremont@…	Adrian Holovaty	"The newforms Select widget (newforms.django.widgets.Select) only renders the select list choices on the first call when using a generator for the choices constructor argument. Here's an example adapted from tests/regressiontests/forms/tests.py:

{{{
>>> def get_choices():
...     for i in range(5):
...         yield (i, i)
>>> w = Select(choices=get_choices())
>>> print w.render('num',2)
<select name=""num"">
<option value=""0"">0</option>
<option value=""1"">1</option>
<option value=""2"" selected=""selected"">2</option>
<option value=""3"">3</option>
<option value=""4"">4</option>
</select>
>>> print w.render('num',2)
<select name=""num"">
</select>
}}}


Platform: Python v. 2.4.3 on cygwin

I think this problem occurs because a generator object created by a generator function or a generator expression can only be iterated over once.

A work-around is to create a sequence type from the generator:


{{{
>>> def get_choices():
...     for i in range(5):
...         yield (i, i)
>>> w = Select(choices=tuple(get_choices()))
>>> print w.render('num',2)
<select name=""num"">
<option value=""0"">0</option>
<option value=""1"">1</option>
<option value=""2"" selected=""selected"">2</option>
<option value=""3"">3</option>
<option value=""4"">4</option>
</select>
>>> print w.render('num',2)
<select name=""num"">
<option value=""0"">0</option>
<option value=""1"">1</option>
<option value=""2"" selected=""selected"">2</option>
<option value=""3"">3</option>
<option value=""4"">4</option>
</select>
}}}

The documentation should either state that the choices argument to Select.__init__() should not be a generator, or the widget should convert the generator object to a sequence and save a copy so that the behavior of Select.render() is consistent regardless of how many times it is called."	defect	closed	Forms	dev	normal	fixed	newforms  Select  widget		Accepted	0	0	0	0	0	0