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
14823	Unexpected behavior with core.serializers.register_serializer and unregister_serializer	miker985@…	nobody	"Almost all the functions in {{{serializers/__init__.py}}} begin with the lines
{{{
if not _serializers:
    _load_serializers()
}}}
but register_serializer and unregister_serializer do not.

When only using the built-in serializers you didn't have to manually register them but if you used an additional serializer you either have to

 1. Include it in settings.SERIALIZATION_MODULES (probably the ""right way"" to do things, but then why make register_serializer public?)
 1. call _load_serializers (non-public API)
 1. manually register both the built-ins and those listed in settings.SERIALIZATION_MODULES (duplicating _load_serializers)
 1. call any public function in {{{__init__.py}}} except register_serializer or unregister_serializer before registering (strange order of operations)

To reproduce (from a fresh `python manage.py shell`)
{{{
from django.core import serializers
serializers.register_serializer('json2', 'django.core.serializers.json')
serializers.get_public_serializer_formats() # ['json2']
serializers.get_serializer('xml') # KeyError: 'xml'
}}}

I've attached a patch that adds the same {{{if not _serializers:}}} check for register_serializer and unregister_serializer. It keeps with the general mentality of the existing code (e.g., not using a separate boolean value to check for registration) but introduces an edge case where code that attempts to unregister all built-in serializers before registering it's own will effectively do nothing. e.g.

{{{
from django.core import serializers
serializers.unregister_serializer('json') # loads json/python/xml (assume no yaml), then unregisters json
serializers.unregister_serializer('xml')
serializers.unregister_serializer('python') # _serializers is now an empty dict
serializers.register_serializer('foo', 'foo.bar.baz') # re-registers json/python/xml, then registers foo.
}}}
Under the existing code you'd get a {{{KeyError}}} when attempting to unregister json (since it hasn't been loaded yet).

Alternatively, it could be determined that register_serializer and unregister_serializer aren't stable API (they're not documented on the Serialization topic page). If that's the case it may make more sense to just prefix them with an _ and/or leave a note similar to the thread-safe notes."		closed	Core (Serialization)	dev		fixed			Ready for checkin	1	0	0	0	0	0