Fixed a regression caused by :ticket:`2410` whereby a

:class:`.CheckConstraint` would apply itself back to the
original table during a :meth:`.Table.tometadata` operation, as
it would parse the SQL expression for a parent table. The
operation now copies the given expression to correspond to the
new table.
[ticket:2633]

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/sqlalchemy/util/langhelpers.py b/lib/sqlalchemy/util/langhelpers.py
index f43cb0b3a..203b39c37 100644
--- a/lib/sqlalchemy/util/langhelpers.py
+++ b/lib/sqlalchemy/util/langhelpers.py
@@ -303,6 +303,8 @@ def generic_repr(obj, additional_kw=(), to_inspect=None):
     if to_inspect is None:
         to_inspect = obj
 
+    missing = object()
+
     def genargs():
         try:
             (args, vargs, vkw, defaults) = \
@@ -322,16 +324,16 @@ def generic_repr(obj, additional_kw=(), to_inspect=None):
                 yield repr(getattr(obj, arg, None))
             for (arg, defval) in zip(args[-default_len:], defaults):
                 try:
-                    val = getattr(obj, arg, None)
-                    if val != defval:
+                    val = getattr(obj, arg, missing)
+                    if val is not missing and val != defval:
                         yield '%s=%r' % (arg, val)
                 except:
                     pass
         if additional_kw:
             for arg, defval in additional_kw:
                 try:
-                    val = getattr(obj, arg, None)
-                    if val != defval:
+                    val = getattr(obj, arg, missing)
+                    if val is not missing and val != defval:
                         yield '%s=%r' % (arg, val)
                 except:
                     pass