Merge pull request #2378 from miguelgrinberg/default-flask-app

Import app from wsgi.py or app.py if FLASK_APP is not defined

docs/cli.rst

@@ -25,10 +25,14 @@ your Flask application's :attr:`Flask.cli` instance as well as some
 built-in commands that are always there.  Flask extensions can also
 register more commands there if they desire so.
 
-For the :command:`flask` script to work, an application needs to be
-discovered.  This is achieved by exporting the ``FLASK_APP`` environment
-variable.  It can be either set to an import path or to a filename of a
-Python module that contains a Flask application.
+For the :command:`flask` script to work, an application needs to be discovered.
+Flask looks for a module named :file:`wsgi.py` or :file:`app.py` by default,
+and if it finds one it assumes the application is defined in it.
+
+You can instruct Flask to look for the application in a different module by
+exporting the ``FLASK_APP`` environment variable. It can be either set to an
+import path or to a filename of a Python module that contains a Flask
+application.
 
 In that imported file the name of the app needs to be called ``app`` or
 optionally be specified after a colon.  For instance

flask/cli.py

@@ -172,13 +172,16 @@ def prepare_exec_for_file(filename):
         if not os.path.isfile(os.path.join(dirpath, '__init__.py')):
             break
 
-    sys.path.insert(0, dirpath)
+    if sys.path[0] != dirpath:
+        sys.path.insert(0, dirpath)
+
     return '.'.join(module[::-1])
 
 
-def locate_app(script_info, app_id):
+def locate_app(script_info, app_id, raise_if_not_found=True):
     """Attempts to locate the application."""
     __traceback_hide__ = True
+
     if ':' in app_id:
         module, app_obj = app_id.split(':', 1)
     else:
@@ -192,15 +195,23 @@ def locate_app(script_info, app_id):
         # Determine this by checking whether the trace has a depth > 1.
         if sys.exc_info()[-1].tb_next:
             stack_trace = traceback.format_exc()
-            raise NoAppException('There was an error trying to import'
-                    ' the app (%s):\n%s' % (module, stack_trace))
+            raise NoAppException(
+                'There was an error trying to import the app ({module}):\n'
+                '{stack_trace}'.format(
+                    module=module, stack_trace=stack_trace
+                )
+            )
+        elif raise_if_not_found:
+            raise NoAppException(
+                'The file/path provided (%s) does not appear to exist. Please'
+                ' verify the path is correct. If app is not on PYTHONPATH,'
+                ' ensure the extension is .py.'.format(module=module)
+            )
         else:
-            raise NoAppException('The file/path provided (%s) does not appear'
-                                 ' to exist.  Please verify the path is '
-                                 'correct.  If app is not on PYTHONPATH, '
-                                 'ensure the extension is .py' % module)
+            return
 
     mod = sys.modules[module]
+
     if app_obj is None:
         return find_best_app(script_info, mod)
     else:
@@ -326,14 +337,26 @@ class ScriptInfo(object):
         if self.create_app is not None:
             rv = call_factory(self.create_app, self)
         else:
-            if not self.app_import_path:
+            if self.app_import_path:
+                rv = locate_app(self, self.app_import_path)
+            else:
+                for module in ['wsgi.py', 'app.py']:
+                    import_path = prepare_exec_for_file(module)
+                    rv = locate_app(
+                        self, import_path, raise_if_not_found=False
+                    )
+
+                    if rv:
+                        break
+
+            if not rv:
                 raise NoAppException(
                     'Could not locate Flask application. You did not provide '
-                    'the FLASK_APP environment variable.\n\nFor more '
-                    'information see '
-                    'http://flask.pocoo.org/docs/latest/quickstart/')
-
-            rv = locate_app(self, self.app_import_path)
+                    'the FLASK_APP environment variable, and a wsgi.py or '
+                    'app.py module was not found in the current directory.\n\n'
+                    'For more information see '
+                    'http://flask.pocoo.org/docs/latest/quickstart/'
+                )
 
         debug = get_debug_flag()
 

tests/test_apps/helloworld/hello.py

@@ -0,0 +1,6 @@
+from flask import Flask
+app = Flask(__name__)
+
+@app.route("/")
+def hello():
+    return "Hello World!"

tests/test_apps/helloworld/wsgi.py

@@ -0,0 +1 @@
+from hello import app

tests/test_cli.py

@@ -181,6 +181,9 @@ def test_locate_app(test_apps):
         script_info, "cliapp.factory:create_app ()")
     pytest.raises(
         NoAppException, locate_app, script_info, "cliapp.importerrorapp")
+    assert locate_app(
+        script_info, "notanpp.py", raise_if_not_found=False
+    ) is None
 
 
 def test_find_default_import_path(test_apps, monkeypatch, tmpdir):
@@ -214,7 +217,7 @@ def test_get_version(test_apps, capsys):
     assert py_ver in out
 
 
-def test_scriptinfo(test_apps):
+def test_scriptinfo(test_apps, monkeypatch):
     """Test of ScriptInfo."""
     obj = ScriptInfo(app_import_path="cliapp.app:testapp")
     assert obj.load_app().name == "testapp"
@@ -228,6 +231,25 @@ def test_scriptinfo(test_apps):
     assert app.name == "createapp"
     assert obj.load_app() == app
 
+    obj = ScriptInfo()
+    pytest.raises(NoAppException, obj.load_app)
+
+    # import app from wsgi.py in current directory
+    monkeypatch.chdir(os.path.abspath(os.path.join(
+        os.path.dirname(__file__), 'test_apps', 'helloworld'
+    )))
+    obj = ScriptInfo()
+    app = obj.load_app()
+    assert app.name == 'hello'
+
+    # import app from app.py in current directory
+    monkeypatch.chdir(os.path.abspath(os.path.join(
+        os.path.dirname(__file__), 'test_apps', 'cliapp'
+    )))
+    obj = ScriptInfo()
+    app = obj.load_app()
+    assert app.name == 'testapp'
+
 
 def test_with_appcontext(runner):
     """Test of with_appcontext."""