Fixed empty strings handling in composite caster

Closes ticket #141.

NEWS

@@ -33,6 +33,7 @@ What's new in psycopg 2.4.5
   - Discard any result produced by 'executemany()' (ticket #133).
   - Fixed pickling of FixedOffsetTimezone objects (ticket #135).
   - Release the GIL around PQgetResult calls after COPY (ticket #140).
+  - Fixed empty strings handling in composite caster (ticket #141).
 
 
 What's new in psycopg 2.4.5

lib/extras.py

@@ -852,9 +852,9 @@ class CompositeCaster(object):
         for m in self._re_tokenize.finditer(s):
             if m is None:
                 raise psycopg2.InterfaceError("can't parse type: %r" % s)
-            if m.group(1):
+            if m.group(1) is not None:
                 rv.append(None)
-            elif m.group(2):
+            elif m.group(2) is not None:
                 rv.append(self._re_undouble.sub(r"\1", m.group(2)))
             else:
                 rv.append(m.group(3))

tests/test_types_extras.py

@@ -501,6 +501,7 @@ class AdaptTypeTestCase(unittest.TestCase):
             self.assertEqual(CompositeCaster.tokenize(s), v)
 
         ok("(,)", [None, None])
+        ok('(,"")', [None, ''])
         ok('(hello,,10.234,2010-11-11)', ['hello', None, '10.234', '2010-11-11'])
         ok('(10,"""")', ['10', '"'])
         ok('(10,",")', ['10', ','])
@@ -555,6 +556,26 @@ class AdaptTypeTestCase(unittest.TestCase):
             self.assertEqual(v.astring, "hello")
             self.assertEqual(v.adate, date(2011,1,2))
 
+    @skip_if_no_composite
+    def test_empty_string(self):
+        # issue #141
+        self._create_type("type_ss", [('s1', 'text'), ('s2', 'text')])
+        curs = self.conn.cursor()
+        psycopg2.extras.register_composite("type_ss", curs)
+
+        def ok(t):
+            curs.execute("select %s::type_ss", (t,))
+            rv = curs.fetchone()[0]
+            self.assertEqual(t, rv)
+
+        ok(('a', 'b'))
+        ok(('a', ''))
+        ok(('', 'b'))
+        ok(('a', None))
+        ok((None, 'b'))
+        ok(('', ''))
+        ok((None, None))
+
     @skip_if_no_composite
     def test_cast_nested(self):
         self._create_type("type_is",