Accommodate tuples for ColumnDefault.__repr__

Fixed bug where ``__repr__`` of :class:`.ColumnDefault` would fail
if the argument were a tuple.  Pull request courtesy Nicolas Caniart.

Change-Id: I08aa2448ef91054c43d6068ac54cedbdf7a83d64
Pull-request: https://bitbucket.org/zzzeek/sqlalchemy/pull-requests/1
Fixes: #4126
(cherry picked from commit 5acc9b149a)

doc/build/changelog/unreleased_11/4126.rst

@@ -0,0 +1,7 @@
+.. change::
+    :tags: bug, sql
+    :tickets: 4126
+    :versions: 1.2.0b4
+
+    Fixed bug where ``__repr__`` of :class:`.ColumnDefault` would fail
+    if the argument were a tuple.  Pull request courtesy Nicolas Caniart.

lib/sqlalchemy/sql/schema.py

@@ -2081,7 +2081,7 @@ class ColumnDefault(DefaultGenerator):
     __visit_name__ = property(_visit_name)
 
     def __repr__(self):
-        return "ColumnDefault(%r)" % self.arg
+        return "ColumnDefault(%r)" % (self.arg, )
 
 
 class Sequence(DefaultGenerator):

test/sql/test_metadata.py

@@ -550,6 +550,7 @@ class MetaDataTest(fixtures.TestBase, ComparesTables):
              "CheckConstraint("
              "%s"
              ", name='someconstraint')" % repr(ck.sqltext)),
+            (ColumnDefault(('foo', 'bar')), "ColumnDefault(('foo', 'bar'))")
         ):
             eq_(
                 repr(const),