Fixes stdout --sql output in python2

When output_encoding is set, wraps the output buffer into a io.TextIOWrapper class
This means that the output_buffer has to be a io.IOBase instance
in order to work along with the TextIOWrapper

Handles wrapping when the buffer is Python2 stdtout, which has 'file' type
Adds test for this situation

1 files changed, 6 insertions, 5 deletions

diff --git a/alembic/migration.py b/alembic/migration.py
index 2b47c91..657e60d 100644
--- a/alembic/migration.py
+++ b/alembic/migration.py
@@ -6,7 +6,7 @@ from sqlalchemy import MetaData, Table, Column, String, literal_column
 from sqlalchemy import create_engine
 from sqlalchemy.engine import url as sqla_url
 
-from .compat import callable
+from .compat import callable, writable_buffer
 from . import ddl, util
 
 log = logging.getLogger(__name__)
@@ -71,13 +71,14 @@ class MigrationContext(object):
             self.connection = connection
         self._migrations_fn = opts.get('fn')
         self.as_sql = as_sql
+
         self.output_buffer = opts.get("output_buffer", sys.stdout)
 
-        if opts.get('output_encoding'):
+        if "output_encoding" in opts:
             self.output_buffer = io.TextIOWrapper(
-                                    self.output_buffer,
-                                    opts['output_encoding']
-                                )
+                opts.get("output_buffer") or writable_buffer(sys.stdout),
+                opts.get('output_encoding')
+            )
 
         self._user_compare_type = opts.get('compare_type', False)
         self._user_compare_server_default = opts.get(