dictsort and dictsortreversed template filters broken

[ionut bizau]

Using dictsort or dictsortreversed template filters for a list of dictionaries which contain dates will break if some of the dates are None, even if the sort field is not one of the date fields! This happens when the list contains at least two dictionaries for which the sort keys are equal.

Example:

In [1]: from django.template import defaultfilters

In [3]: from datetime import datetime

In [4]: defaultfilters.dictsort([{'a': 1, 'b': datetime.now()}, {'a': 2, 'b': None}, {'a': 1, 'b': None}], "a")
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/XXX/<ipython console> in <module>()

/System/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/django/template/defaultfilters.pyc in dictsort(value, arg)
    470     var_resolve = Variable(arg).resolve
    471     decorated = [(var_resolve(item), item) for item in value]
--> 472     decorated.sort()
    473     return [item[1] for item in decorated]
    474 dictsort.is_safe = False

TypeError: can't compare datetime.datetime to NoneType

My patch fixes this problem for both dictsort and dictsortreversed.

[ionut bizau]

@Alex What's wrong with my patch?

[Alex Gaynor]

It should use the key argument, not the cmp one, as cmp has been deprecated. It also lacks tests.

[Chris Beaven]

Where do the Python docs say cmp has been deprecated? At the very least, they show that key was introduced in 2.4 so we can't rely on that.

[ionut bizau]

OK. I was afraid to use key for compatibility reasons (Python 2.3 doesn't support it). Will look into the tests.

[ionut bizau]

It's only been deprecated since 2.6. So it's a question of whether Django needs to run on 2.3 or not. Also, seems cmp will be removed from 3.0. Does Django support 3.0 officially?

[Alex Gaynor]

Oh, I hadn't realized 2.3 didn't have it, though Django 1.1 will support 2.3, this almost certainly won't get in until 1.2 at which point 2.3 will no longer be supported.

[eronen]

The patch here fixes another problem in dictsort, too: unlike Python's sort,
it's not stable sort (doesn't preserve the order when the sorting key is the same).
See ticket #12110.

[nathan]

I've run into this on numerous occasions. Any idea on when this'll be applied?

[Julien Phalip]

This is actually working fine now. Probably fixed in [15316].