TypeError: unorderable types: SequencePath() < SequencePath()

[jpotoniec]

Hi,
I believe there is some error in the SPARQL parser during reordering triples with property paths
Minimal working example leading to the error:

#!/usr/bin/env python3

import rdflib

query = '''
prefix owl: <http://www.w3.org/2002/07/owl#> 
prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
select ?x
where
{   
    ?x rdf:rest/rdf:first _:6.
    ?x rdf:rest/rdf:first _:5.
}
'''
print(rdflib.__version__)
g = rdflib.Graph()
result = g.query(query)

I am using rdflib installed with pip as described in README. The output of the above script is:

4.2.0
Traceback (most recent call last):
  File "./query.py", line 17, in <module>
    result = g.query(query)
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/graph.py", line 1080, in query
    query_object, initBindings, initNs, **kwargs))
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/plugins/sparql/processor.py", line 73, in query
    query = translateQuery(parsetree, base, initNs)
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/plugins/sparql/algebra.py", line 744, in translateQuery
    P, PV = translate(q[1])
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/plugins/sparql/algebra.py", line 533, in translate
    M = translateGroupGraphPattern(q.where)
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/plugins/sparql/algebra.py", line 278, in translateGroupGraphPattern
    g[-1]["triples"] += triples(p.triples)
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/plugins/sparql/algebra.py", line 131, in triples
    for x in range(0, len(l), 3))
  File "/home/smaug/tmp/venv/lib/python3.4/site-packages/rdflib/plugins/sparql/algebra.py", line 113, in reorderTriples
    1], varsknown, varscount), x[1]) for x in l[i:])
TypeError: unorderable types: SequencePath() < SequencePath()

I am to believe that the syntax of the SPARQL query is correct, as other SPARQL engines can deal with it (e.g. http://factforge.net/sparql?sample=prefix+owl%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F2002%2F07%2Fowl%23%3E+%0D%0Aprefix+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E%0D%0Aselect+%3Fx%0D%0Awhere%0D%0A%7B+++%0D%0A++++%3Fx+rdf%3Arest%2Frdf%3Afirst+_%3A6.%0D%0A++++%3Fx+rdf%3Arest%2Frdf%3Afirst+_%3A5.%0D%0A%7D%0D%0Alimit+1)

[gromgull]

Yep - someone has to make up some kind of ordering and implement __lt__ for the path objects.

[bollwyvl]

Wow, this hit me like a train. How can I help?

[joernhees]

just make a pull request? sorry, i didn't find any time to think about this yet

[bollwyvl]

Is there another implementation i should look at for guidance?

On 09:04, Fri, Sep 18, 2015 Jörn Hees notifications@github.com wrote:

just make a pull request? sorry, i didn't find any time to think about
this yet

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#492 (comment).

[joernhees]

i guess all of https://github.com/RDFLib/rdflib/blob/master/rdflib/plugins/sparql/algebra.py and https://github.com/RDFLib/rdflib/tree/master/rdflib/plugins/sparql/operators.py

[gromgull]

No no - it's actually very easy. On py2 everything is orderable:

In [26]: RDF.type/RDF.first
Out[26]: Path(http://www.w3.org/1999/02/22-rdf-syntax-ns#type /
http://www.w3.org/1999/02/22-rdf-syntax-ns#first)

In [27]: p1 = RDF.type/RDF.first

In [28]: p2 = RDF.type|RDF.first

In [29]: p2
Out[29]: Path(http://www.w3.org/1999/02/22-rdf-syntax-ns#type |
http://www.w3.org/1999/02/22-rdf-syntax-ns#first)

In [30]: p1>p2
Out[30]: False

In [31]: p2<p1
Out[31]: False

BUT on py3 only explicitly comparable things are:

p1=RDF.type/RDF.type
p2=RDF.type|RDF.type
p1>p2
Traceback (most recent call last):
File "", line 1, in
TypeError: unorderable types: SequencePath() > AlternativePath()

To fix this you have to implement lt, gt, ge etc.
You can shortcut and only implement equals and lt and use
https://docs.python.org/2/library/functools.html#functools.total_ordering

The actual order doesn't matter, they just have to be sortable, just make
up something.
This is already done for instance for terms:

https://github.com/RDFLib/rdflib/blob/master/rdflib/term.py#L169
and
https://github.com/RDFLib/rdflib/blob/master/rdflib/term.py#L1587-L1593

• Gunnar

On 23 September 2015 at 16:14, Jörn Hees notifications@github.com wrote:

i guess all of
https://github.com/RDFLib/rdflib/blob/master/rdflib/plugins/sparql/algebra.py
and
https://github.com/RDFLib/rdflib/tree/master/rdflib/plugins/sparql/operators.py

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#492 (comment).

http://gromgull.net

[joernhees]

@gromgull thanks for the pointer...

[bollwyvl]

Ah, didn't realize this was a 2/3 issue. I didn't think clause ordering
mattered. Thanks!

On Wed, Sep 23, 2015 at 12:40 PM Jörn Hees notifications@github.com wrote:

@gromgull https://github.com/gromgull thanks for the pointer...

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#492 (comment).