Used CommandError in createcachetable command.

Raising CommandError whenever a management command meets an error
condition is the standard way to handle errors in commands.

django/core/management/commands/createcachetable.py

 from optparse import make_option
 
 from django.core.cache.backends.db import BaseDatabaseCache
-from django.core.management.base import LabelCommand
+from django.core.management.base import LabelCommand, CommandError
 from django.db import connections, router, transaction, models, DEFAULT_DB_ALIAS
 from django.db.utils import DatabaseError
 
@@ -55,11 +55,10 @@ class Command(LabelCommand):
         try:
             curs.execute("\n".join(full_statement))
         except DatabaseError as e:
-            self.stderr.write(
+            transaction.rollback_unless_managed(using=db)
+            raise CommandError(
                 "Cache table '%s' could not be created.\nThe error was: %s." %
                     (tablename, e))
-            transaction.rollback_unless_managed(using=db)
-        else:
-            for statement in index_output:
-                curs.execute(statement)
-            transaction.commit_unless_managed(using=db)
+        for statement in index_output:
+            curs.execute(statement)
+        transaction.commit_unless_managed(using=db)

tests/regressiontests/cache/tests.py

@@ -7,7 +7,6 @@ from __future__ import absolute_import
 import hashlib
 import os
 import re
-import StringIO
 import tempfile
 import time
 import warnings
@@ -820,9 +819,14 @@ class DBCacheTests(BaseCacheTests, TransactionTestCase):
         self.perform_cull_test(50, 18)
 
     def test_second_call_doesnt_crash(self):
-        err = StringIO.StringIO()
-        management.call_command('createcachetable', self._table_name, verbosity=0, interactive=False, stderr=err)
-        self.assertTrue(b"Cache table 'test cache table' could not be created" in err.getvalue())
+        with self.assertRaisesRegexp(management.CommandError,
+                "Cache table 'test cache table' could not be created"):
+            management.call_command(
+               'createcachetable',
+                self._table_name,
+                verbosity=0,
+                interactive=False
+            )
 
 
 @override_settings(USE_TZ=True)