Allow Media objects to have their own MEDIA_TYPES

[Keryn Knight <django@…>]

Currently, ​instances of Media look to the module scope to get the known ​MEDIA_TYPES. This makes it difficult to subclass Media to add extra render_x/add_x methods because MEDIA_TYPES is hardcoded in ​__init__, ​render, ​__getitem__ and ​__add__ and isn't easily available for a subclass to add to without monkeypatching the module constant. As far as I can tell, the only use of MEDIA_TYPES is in the widgets module, and could be shifted to the class itself, leaving the module level one to raise a deprecation warning.

Rationale is that I want to be able to add inline_css and inline_js, or text (for JS templates etc) to a Media object, and currently that's more difficult than just adjusting a subclass' attribute and adding the appropriate methods.

[Aymeric Augustin]

See also #13978.

[Michael Kelly]

Pull request submitted: ​https://github.com/django/django/pull/2562

[Hiroki Kiyohara]

this patch may need improvement.
you should consider the case when combining CustomMedias which has different MEDIA_TYPES,
see more ​https://github.com/django/django/pull/2562#issuecomment-42101462

[Michael Kelly]

Good point! Either throwing an exception on combining Media subclasses with different Media types, or throwing one when there's a name conflict in the MEDIA_TYPES list sound like good options to me; I'd probably lean towards the latter simply because it's more flexible and not really that complex to add.

However, I'm hesitant to make changes to the patch before #22298 is resolved, as if form media is going away, improvements aren't terribly relevant anymore. (I submitted the patch before someone pointed that issue out to me, of course :P).

[Hiroki Kiyohara]

@Osmose thanks for your reply. the after one sounds greater! > throwing one when there's a name conflict in the MEDIA_TYPES list

#22298 discussion looks hassle a little (´Д｀), the patch will probably have to wait for a while.
But you've done a great job. im pretty sure.