Merge pull request #271 from RDFLib/slice

Slices as syntactic sugar for graphs / resources

examples/foafpaths.py

@@ -7,9 +7,9 @@
 
 p1 / p2 => Path sequence
 p1 | p2 => Path alternative
-p1 % '*' => chain of 0 or more p's
-p1 % '+' => chain of 1 or more p's
-p1 % '?' => 0 or 1 p 
+p1 * '*' => chain of 0 or more p's
+p1 * '+' => chain of 1 or more p's
+p1 * '?' => 0 or 1 p 
 ~p1 => p1 is inverted order (s p1 o) <=> (o ~p1 s)
 -p1 => NOT p1, i.e. any property by p1
 

rdflib/graph.py

@@ -365,6 +365,57 @@ def triples(self, (s, p, o)):
         for (s, p, o), cg in self.__store.triples((s, p, o), context=self):
             yield (s, p, o)
 
+    @py3compat.format_doctest_out
+    def __getitem__(self, item): 
+        """
+        A graph can be "sliced" as a shortcut for the triples method
+        The python slice syntax is (ab)used for specifying triples. 
+        A generator over matching triples is returned
+
+        >>> import rdflib
+        >>> g = rdflib.Graph()
+        >>> g.add((rdflib.URIRef('urn:bob'), rdflib.RDFS.label, rdflib.Literal('Bob')))
+
+        >>> list(g[rdflib.URIRef('urn:bob')]) # all triples about bob
+        [(rdflib.term.URIRef(%(u)s'urn:bob'), rdflib.term.URIRef(%(u)s'http://www.w3.org/2000/01/rdf-schema#label'), rdflib.term.Literal(%(u)s'Bob'))]
+        
+        >>> list(g[:rdflib.RDFS.label]) # all label triples
+        [(rdflib.term.URIRef(%(u)s'urn:bob'), rdflib.term.URIRef(%(u)s'http://www.w3.org/2000/01/rdf-schema#label'), rdflib.term.Literal(%(u)s'Bob'))]
+
+        >>> list(g[::rdflib.Literal('Bob')]) # all label triples
+        [(rdflib.term.URIRef(%(u)s'urn:bob'), rdflib.term.URIRef(%(u)s'http://www.w3.org/2000/01/rdf-schema#label'), rdflib.term.Literal(%(u)s'Bob'))]
+
+        Combined with SPARQL paths, more complex queries can be
+        written concisely:
+
+        Name of all Bobs friends: 
+
+        g[bob : FOAF.knows/FOAF.name ]
+
+        Some label for Bob:
+
+        g[bob : DC.title|FOAF.name|RDFS.label]
+
+        All friends and friends of friends of Bob
+
+        g[bob : FOAF.knows * '+']
+
+        etc.
+
+        """
+
+        if isinstance(item, slice): 
+
+            s,p,o=item.start,item.stop,item.step
+            return self.triples((s,p,o))
+
+        elif isinstance(item, Node):
+
+            return self.triples((item,None,None))
+
+        else: 
+            raise TypeError("You can only index a graph by a single rdflib term or a slice of rdflib terms.")
+
     def __len__(self):
         """Returns the number of triples in the graph
 

rdflib/resource.py

@@ -303,7 +303,7 @@
 
 """)
 
-from rdflib.term import BNode, URIRef
+from rdflib.term import Node, BNode, URIRef
 from rdflib.namespace import RDF
 
 __all__ = ['Resource']
@@ -434,6 +434,31 @@ def _cast(self, node):
         else:
             return node
 
+    def __getitem__(self, item):
+        """
+        Resources can be sliced like graphs, but the subject is fixed. 
+        
+        r[RDFS.label] returns triples for (self.identifier, RDFS.label, None)
+        r[RDFS.label : Literal("Bob")] for (self.identifier, RDFS.label, "Bob")
+        etc. 
+
+        """
+
+        if isinstance(item, slice): 
+            if item.step: 
+                raise TypeError("Resources fix the subject for slicing, and can only be sliced by predicate/object. ")
+            p,o=item.start,item.stop
+            s=(self.identifier,)
+            return self.triples((s,p,o))
+
+        elif isinstance(item, Node):
+
+            return self.triples((self.identifier, item, None))
+
+        else: 
+            raise TypeError("You can only index a resource by a single rdflib term, a slice of rdflib terms.")
+
+
     def _new(self, subject):
         return type(self)(self._graph, subject)
 

test/test_slice.py

@@ -0,0 +1,82 @@
+
+from rdflib import Graph, URIRef
+import unittest
+
+class GraphSlice(unittest.TestCase):
+
+    def testSlice(self):
+        """
+         We pervert the slice object, 
+         and use start, stop, step as subject, predicate, object
+
+         all operations return generators over full triples 
+        """
+
+        sl=lambda x,y: self.assertEquals(len(list(x)),y)
+        soe=lambda x,y: self.assertEquals(set([a[2] for a in x]),set(y)) # equals objects
+        g=self.graph
+
+        # Single terms are all trivial:
+
+        # single index slices by subject, i.e. return triples((x,None,None))
+        # tell me everything about "tarek"
+        sl(g[self.tarek],2)
+
+        # single slice slices by s,p,o, with : used to split
+        # tell me everything about "tarek" (same as above)
+        sl(g[self.tarek::],2)
+
+        # give me every "likes" relationship
+        sl(g[:self.likes:],5)
+
+        # give me every relationship to pizza
+        sl(g[::self.pizza],3)
+
+        # give me everyone who likes pizza
+        sl(g[:self.likes:self.pizza],2)
+
+        # does tarek like pizza?
+        sl(g[self.tarek:self.likes:self.pizza],1)
+
+        # More intesting is using paths
+
+        # everything hated or liked
+        sl(g[:self.hates|self.likes], 7)
+
+
+
+
+
+    def setUp(self):
+        self.graph = Graph()
+
+        self.michel = URIRef(u'michel')
+        self.tarek = URIRef(u'tarek')
+        self.bob = URIRef(u'bob')
+        self.likes = URIRef(u'likes')
+        self.hates = URIRef(u'hates')
+        self.pizza = URIRef(u'pizza')
+        self.cheese = URIRef(u'cheese')
+
+        self.addStuff()
+
+    def addStuff(self):
+        tarek = self.tarek
+        michel = self.michel
+        bob = self.bob
+        likes = self.likes
+        hates = self.hates
+        pizza = self.pizza
+        cheese = self.cheese
+
+        self.graph.add((tarek, likes, pizza))
+        self.graph.add((tarek, likes, cheese))
+        self.graph.add((michel, likes, pizza))
+        self.graph.add((michel, likes, cheese))
+        self.graph.add((bob, likes, cheese))
+        self.graph.add((bob, hates, pizza))
+        self.graph.add((bob, hates, michel)) # gasp!
+
+
+if __name__ == '__main__':
+    unittest.main()