Correctly detect an empty query sent to the backend

Closes ticket #46.

NEWS

@@ -1,3 +1,9 @@
+What's new in psycopg 2.4.1
+---------------------------
+
+  - Correctly detect an empty query sent to the backend (ticket #46).
+
+
 What's new in psycopg 2.4
 -------------------------
 

psycopg/pqpath.c

@@ -1359,6 +1359,13 @@ pq_fetch(cursorObject *curs)
         /* don't clear curs->pgres, because it contains the results! */
         break;
 
+    case PGRES_EMPTY_QUERY:
+        PyErr_SetString(ProgrammingError,
+            "can't execute an empty query");
+        IFCLEARPGRES(curs->pgres);
+        ex = -1;
+        break;
+
     default:
         Dprintf("pq_fetch: uh-oh, something FAILED: pgconn = %p", curs->conn);
         pq_raise(curs->conn, curs, NULL);

tests/test_cursor.py

@@ -37,6 +37,12 @@ class CursorTests(unittest.TestCase):
     def tearDown(self):
         self.conn.close()
 
+    def test_empty_query(self):
+        cur = self.conn.cursor()
+        self.assertRaises(psycopg2.ProgrammingError, cur.execute, "")
+        self.assertRaises(psycopg2.ProgrammingError, cur.execute, " ")
+        self.assertRaises(psycopg2.ProgrammingError, cur.execute, ";")
+
     def test_executemany_propagate_exceptions(self):
         conn = self.conn
         cur = conn.cursor()