adjust for loop style

CHANGES

@@ -40,8 +40,8 @@ Major release, unreleased
 - Allow IP address as exact session cookie domain. (`#2282`_)
 - ``SESSION_COOKIE_DOMAIN`` is set if it is detected through ``SERVER_NAME``.
   (`#2282`_)
-- Auto-detect 0-argument app factory called ``create_app`` or ``make_app`` from
-  ``FLASK_APP``. (`#2297`_)
+- Auto-detect zero-argument app factory called ``create_app`` or ``make_app``
+  from ``FLASK_APP``. (`#2297`_)
 
 .. _#1489: https://github.com/pallets/flask/pull/1489
 .. _#1898: https://github.com/pallets/flask/pull/1898

flask/cli.py

@@ -35,7 +35,7 @@ def find_best_app(module):
     from . import Flask
 
     # Search for the most common names first.
-    for attr_name in 'app', 'application':
+    for attr_name in ('app', 'application'):
         app = getattr(module, attr_name, None)
         if isinstance(app, Flask):
             return app
@@ -55,7 +55,7 @@ def find_best_app(module):
         )
 
     # Search for app factory callables.
-    for attr_name in 'create_app', 'make_app':
+    for attr_name in ('create_app', 'make_app'):
         app_factory = getattr(module, attr_name, None)
 
         if callable(app_factory):