Fixes #355: Python2 buffer PrimaryKey returns as read-write buffer

pony/orm/dbapiprovider.py

@@ -641,7 +641,8 @@ def validate(converter, val, obj=None):
         if isinstance(val, str): return buffer(val)
         throw(TypeError, "Attribute %r: expected type is 'buffer'. Got: %r" % (converter.attr, type(val)))
     def sql2py(converter, val):
-        if not isinstance(val, buffer):
+        if not isinstance(val, buffer) or \
+                (PY2 and converter.attr.pk_offset is not None and 'read-write' in repr(val)):  # Issue 355
             try: val = buffer(val)
             except: pass
         return val

pony/orm/tests/test_bug_355.py

@@ -0,0 +1,23 @@
+import unittest
+
+from pony import orm
+from pony.py23compat import buffer
+
+class Test(unittest.TestCase):
+    def test_1(self):
+        db = orm.Database('sqlite', ':memory:')
+
+        class Buf(db.Entity):
+            pk = orm.PrimaryKey(buffer)
+
+        db.generate_mapping(create_tables=True)
+
+        x = buffer(b'123')
+
+        with orm.db_session:
+            Buf(pk=x)
+            orm.commit()
+
+        with orm.db_session:
+            t = Buf[x]
+