Select widget doesn't accept non-string as value

[Nguyễn Hồng Quân]

I made a model, with age_bracket field, which accepts values from choices like this:

AGE_BRACKET = (
    # The value in the first column will be saved in Postgres Range field,
    # so the upper boundary is not counted, i.e for (18, 25) range, the value 25
    # is not counted.
    ((None, 18), _('Under 18')),
    ((18, 25), _('18 - 24')),
    ((25, 36), _('25 - 35')),
    ((36, 46), _('36 - 45')),
    ((46, 56), _('46 - 55')),
    ((46, 66), _('56 - 65')),
    ((66, None), _('Above 65')),
)

However, when being rendered as form, all values become empty string. This happens since Django 1.11. In Django 1.10, it was OK.
I found the cause is the widget template select_option.html

<option value="{{ widget.value|stringformat:'s' }}"{% include "django/forms/widgets/attrs.html" %}>{{ widget.label }}</option>

The stringformat filter turns every non-string value to empty string.
My suggestion is that, update stringformat so that it returns str(value) if value is not a string. Is it right way to do?

[Claude Paroz]

I also think that stringformat should be improved to accept tuples as its base value. In Python the printf syntax special cases tuples as it considers them as a list of placeholder values. This does not make sense in stringformat as the string containing the placeholder is always a single placeholder.

[Srinivas Reddy Thatiparthy]

PR - ​https://github.com/django/django/pull/8914

[Claude Paroz <claude@…>]

In a64f88f:

Refs #28502 -- Completed stringformat filter tests

[Claude Paroz <claude@…>]

In 4ead705c:

Fixed #28502 -- Made stringformat template filter accept tuples

[Tim Graham <timograham@…>]

In ed77bea:

Refs #28502 -- Complemented stringformat tuple handling/test.

An additional test and a code change were suggested in a late review.

[Tim Graham <timograham@…>]

In dd82f1df:

[1.11.x] Fixed #28502 -- Made stringformat template filter accept tuples.

Backport of 4ead705cb3cf04bb7551ac037d1e11f682b62bcf and
ed77bea58274e11e5a9e4c8b9650f50deb8a2b26 from master