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
14039	FileField special-casing breaks MultiValueField including a FileField	Carl Meyer	Carl Meyer	"There are a couple places where !FileField is special-cased using {{{ isinstance }}} in the forms code: specifically, in [[http://code.djangoproject.com/browser/django/trunk/django/forms/forms.py#L280 BaseForm._clean_fields]], a !FileField's clean method is passed the initial value as well as the data, and in [[http://code.djangoproject.com/browser/django/trunk/django/forms/forms.py#L438 BoundField.as_widget ]] the initial value is used as the rendered data even when the form is bound.

This handling of !FileFields is correct, and makes them behave more naturally with redisplayed bound forms. But, as usual, the use of {{{ isinstance }}} makes things more brittle than necessary. Specifically, in [[http://bitbucket.org/carljm/django-form-utils django-form-utils]] I've implemented a !ClearableFileField via !MultiValueField and !MultiWidget (because the !ClearableFileField contains both a !FileField and a checkbox for clearing it). The isinstance special-casing means the !ClearableFileField can't get the right behavior to parallel a !FileField (because it's not a !FileField subclass, it's a !MultiValueField subclass containing a !FileField).

It would be better if the special !FileField behavior were implemented with a class attribute flag or a polymorphic method on Field, rather than an {{{ isinstance }}} check, so that any field could trigger the appropriate behavior regardless of its inheritance ancestry.

(This is obviously low priority, not expecting anyone else to work on it, just recording it here as a I may find some time to work on a patch)."	Bug	new	Forms	dev	Normal		sprintSep2010	mail@… bradleyayers	Accepted	1	1	0	0	0	0