The plug-in serializers are listed in rdfextras.plugins:
register('n3', Serializer,
'rdflib.plugins.serializers.n3','N3Serializer')
register('turtle', Serializer,
'rdflib.plugins.serializers.turtle', 'TurtleSerializer')
register('nt', Serializer,
'rdflib.plugins.serializers.nt', 'NTSerializer')
register('xml', Serializer,
'rdflib.plugins.serializers.rdfxml', 'XMLSerializer')
register('pretty-xml', Serializer,
'rdflib.plugins.serializers.rdfxml', 'PrettyXMLSerializer')
register('trix', Serializer,
'rdflib.plugins.serializers.trix', 'TriXSerializer')
register('nquads', Serializer,
'rdflib.plugins.serializers.nquads', 'NQuadsSerializer')
ConjunctiveGraph().parse(data=s, format='n3')
ConjunctiveGraph().parse(data=s, format='nquads')
ConjunctiveGraph().parse(data=s, format='nt')
ConjunctiveGraph().parse(data=s, format='xml')
ConjunctiveGraph().parse(data=s, format='trix')
ConjunctiveGraph().parse(data=s, format='turtle')
ConjunctiveGraph().parse(data=s, format='pretty-xml')