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
22412	Clarify expectation around template filters and exceptions	Carl Meyer	nobody	"In the [https://docs.djangoproject.com/en/1.4/howto/custom-template-tags/#writing-custom-template-filters custom template filters documentation], we say ""Filter functions should always return something. They shouldn’t raise exceptions. They should fail silently. In case of error, they should return either the original input or an empty string – whichever makes more sense.""

Then we immediately proceed to show (with approval, not as a counter-example) a template filter which fails to implement this recommendation. (If passed anything without a `replace` method, it will fail loudly.)

If we really mean to say that template filters should never raise exceptions, then a) we should provide a utility decorator that helps to implement that recommendation (something like [https://github.com/mariocesar/sorl-thumbnail/blob/master/sorl/thumbnail/templatetags/thumbnail.py#L26 sorl-thumbnail's safe_filter]), and we should use it in all of our example filters.

Personally I think this is a bad recommendation and we should change it. Template filters, like any other code, should catch errors that they can reasonably expect and handle with a fallback value, but a blanket catching of all exceptions is just as bad in template filters as in any other code (because it is likely to hide bugs)."	Cleanup/optimization	closed	Documentation	1.6	Normal	fixed			Ready for checkin	0	0	0	0	0	0