rdflib.collections issues

[gromgull]

Adding the same element twice to a collection triggers an exception when serializing the graph, but this shouldn't be a problem:

/usr/local/lib/python2.7/dist-packages/rdflib/collection.pyc in __len__(self)
     77         links=set()
     78         for item in self.graph.items(self.uri):
---> 79             assert item not in links,"There is a loop in the RDF list! (%s has been processed before)"%item
     80             links.add(item)
     81             count += 1

AssertionError: There is a loop in the RDF list! (http://www.w3.org/2000/01/rdf-schema#Class has been processed before)

There is also no way to close the list, appending RDF.nil adds another bnode with first->nil and rest->nil.

[gromgull]

Also, no type rdf:List statement is added ...

[gromgull]

Correction, the list is ALWAYS closed (nil is always the rest of the last element), there is no way to leave the list open though.

[wwaites]

This one just bit me

[gromgull]

@wwaites if you find a fix in the next weeks we can get it into 4.2.2!

[wwaites]

Near as I can tell, it is safe to remove this assertion. Graph.items checks for recursion on the list structure itself . This check is simply incorrect for rdf:List that is quite unrestricted. There is no type that I know of with set semantics so I can't see where the assertion can ever be correct even for containers.