Fix parser bug and add test (#2943)

* Fix parser bug and add test

* Fix import order in unrelated file to make CI happy

* Simply fix, add explanatory comment

* Apply black formatter

---------

Co-authored-by: Ashley Sommer <[email protected]>

Author: bovlb

rdflib/plugins/sparql/parser.py

@@ -81,7 +81,11 @@ def expandTriples(terms: ParseResults) -> List[Any]:
                 if len(t) > 1:
                     res += t  # Don't update last_subject/last_predicate
                 # is this bnode the subject of more triples?
-                if i + 1 < l_ and terms[i + 1] not in ".,;":
+                if i + 1 < l_ and terms[i + 1] not in [
+                    ".",
+                    ",",
+                    ";",
+                ]:  # term might not be a string
                     last_subject, last_predicate = t[0], None
                     res.append(t[0])
             elif isinstance(t, ParseResults):

test/data/translate_algebra/test_graph_patterns__bnode_subject.txt

@@ -0,0 +1,4 @@
+PREFIX : <http://example.org/>
+SELECT ?x ?y WHERE {
+[ :p1 ?x ] :p2 ?y .
+}

test/test_sparql/test_translate_algebra.py

@@ -105,6 +105,10 @@ def _format_query(query: str) -> str:
         "test_graph_patterns__bgp",
         "Test if basic graph patterns are properly translated into the query text.",
     ),
+    AlgebraTest(
+        "test_graph_patterns__bnode_subject",
+        "Test if a blank node subject gets properly translated into the query text.",
+    ),
     AlgebraTest(
         "test_graph_patterns__extend",
         'Test if "extend" (=Bind explicitly or implicitly in projection)'