When number argument is not an integer ungettext_lazy's return value evaluates to False

[Michał Przybyś]

When I tried to pass ungettext_lazy as the message argument for MinLengthValidator:

MinLengthValidator(4, ungettext_lazy(
    'Name has to be at least %(limit_value)d character long.',
    'Name has to be at least %(limit_value)d characters long.', 'limit_value'
))

the default message was still used. After fiddling around I found out, that it's because ungettext_lazy's return value's __len__ returns 0 which makes it evaluate to False and fail a check in BaseValidator's constructor.

>>> len(ungettext_lazy('%(number)d object', '%(number)d objects', 'number'))
0
>>> len(ungettext_lazy('%(number)d object', '%(number)d objects', 1))
17
>>> bool(ungettext_lazy('%(number)d object', '%(number)d objects', 'number'))
False
>>> bool(ungettext_lazy('%(number)d object', '%(number)d objects', 1))
True

I'm not sure if this behaviour is a bug, or is it by design and it's a bug in BaseValidator's constructor, but I assume it's the former.

Using django 1.8.5, checked on python 2.7.9 and 3.4.3.

[Claude Paroz]

Yes, that's a bug. Possible resolution: ​PR

[Claude Paroz <claude@…>]

In 8b5acda:

Fixed #25571 -- Fixed boolean evaluation of ungettext_lazy