Don't require FLASK_APP to have .py extension

CHANGES

@@ -82,6 +82,9 @@ Major release, unreleased
 - Fix incorrect JSON encoding of aware, non-UTC datetimes. (`#2374`_)
 - Template auto reloading will honor the ``run`` command's ``debug`` flag even
   if ``app.jinja_env`` was already accessed. (`#2373`_)
+- The ``flask`` command no longer requires that the ``FLASK_APP`` environment
+  variable have a ``.py`` extension. (`#2383`_)
+
 - The following old deprecated code was removed. (`#2385`_)
 
     - ``flask.ext`` - import extensions directly by their name instead of
@@ -123,6 +126,7 @@ Major release, unreleased
 .. _#2362: https://github.com/pallets/flask/pull/2362
 .. _#2374: https://github.com/pallets/flask/pull/2374
 .. _#2373: https://github.com/pallets/flask/pull/2373
+.. _#2383: https://github.com/pallets/flask/pull/2383
 .. _#2385: https://github.com/pallets/flask/issues/2385
 
 Version 0.12.2

flask/cli.py

@@ -177,6 +177,14 @@ def prepare_exec_for_file(filename):
 
     return '.'.join(module[::-1])
 
+def prepare_exec_for_dir(dirpath):
+    """Given a directory this will put the parent directory on the python path
+    and return the directory name. Used for when FLASK_APP is a module that
+    contains an app
+    """
+    sys.path.append(os.path.join(dirpath, os.pardir))
+    return os.path.basename(dirpath)
+
 
 def locate_app(script_info, app_id, raise_if_not_found=True):
     """Attempts to locate the application."""
@@ -223,8 +231,11 @@ def find_default_import_path():
     app = os.environ.get('FLASK_APP')
     if app is None:
         return
-    if os.path.isfile(app):
-        return prepare_exec_for_file(app)
+    if os.path.isdir(app):
+        return prepare_exec_for_dir(app)
+    for path in [app, app + '.py']:
+        if os.path.isfile(path):
+            return prepare_exec_for_file(path)
     return app