base.Model __str__ sometimes returns unicode on Python 2

[Kevin Turner]

base.py contains from __future__ import unicode_literals

so the "" that Model.__str__ returns is a unicode object in the case where hasattr(self, '__unicode__') is False.

There's a force_text().encode() on the other case; probably both cases should use smart_str.

Discovered under Django 1.7 but this looks to still be the case in the master branch.

[Simon Charette]

Hi @keturn,

Is this just something you assumed from reading the source?

Could you provide a failing test case because from my understanding force_text().encode('utf-8') returns an utf-8 encoded bytestring.

[Simon Charette]

Ahh I think I see what you mean by unicode string returned.

The default __str__ implementation returns u'%s object' % self.__class__.__name__ if not hasattr(self, '__unicode__').

This isn't really an issue because self.__class__.__name__ can only contain ASCII characters on Python 2 and thus the returned string is always successfully coerced to a bytestring when required unless I'm missing something.

It wouldn't hurt to simply prefix the default format with a b but I don't think it's worth a backport. Most calls to __str__ are made implicitly through str() which automatically tries to encode('ascii') when fed unicode which will never fail given the nature of self.__class__.__name__ on Python 2.

[Kevin Turner]

Returning the wrong type will gum things up even if the content of that response is only ascii characters, as in ​this example.

Those format operations aren't always in places where you can change them over to all use __unicode__, because they're embedded in things like ​TestCase messages, which is where I encountered it.

Having the test-failure message fail to format itself and crash is pretty annoying when you're trying to write or fix a test.

(edited to fix URL of example)

[Simon Charette]

Didn't know about Python 2 behavior in this case.

b'%s' % u'foo' # works

b'%s' % u'bär' # works

b'%s' % u'bär'.encode('utf-8') # works

b'%s - %s' % (u'foo', u'bär'.encode('utf-8')) # fails

It looks like this issue exists since we added Python 3 support in Django 1.5

[Simon Charette]

Created a ​PR.

[Simon Charette <charette.s@…>]

In 4cd5d84:

Fixed #25730 -- Made Model.str() always return str instances.

Thanks to Kevin Turner for the report and Tim for the review.

[Simon Charette <charette.s@…>]

In 946e7679:

[1.9.x] Fixed #25730 -- Made Model.str() always return str instances.

Thanks to Kevin Turner for the report and Tim for the review.

Backport of 4cd5d846d4a0a62bba6edf435a8ae9c6dcfacb43 from master