improve find_best_app method

src/flask/cli.py

@@ -30,55 +30,46 @@ class NoAppException(click.UsageError):
 
 
 def find_best_app(module):
-    """Given a module instance this tries to find the best possible
+    """Given a module instance, this function tries to find the best possible
     application in the module or raises an exception.
     """
-    from . import Flask
 
-    # Search for the most common names first.
-    for attr_name in ("app", "application"):
-        app = getattr(module, attr_name, None)
+    def find_app_by_attribute(attr_name):
+        return getattr(module, attr_name, None)
 
-        if isinstance(app, Flask):
-            return app
-
-    # Otherwise find the only object that is a Flask instance.
+    def find_app_by_instance():
         matches = [v for v in module.__dict__.values() if isinstance(v, Flask)]
+        return matches[0] if len(matches) == 1 else None
 
-    if len(matches) == 1:
-        return matches[0]
-    elif len(matches) > 1:
-        raise NoAppException(
-            "Detected multiple Flask applications in module"
-            f" '{module.__name__}'. Use '{module.__name__}:name'"
-            " to specify the correct one."
-        )
-
-    # Search for app factory functions.
-    for attr_name in ("create_app", "make_app"):
+    def find_app_by_factory(attr_name):
         app_factory = getattr(module, attr_name, None)
-
         if inspect.isfunction(app_factory):
             try:
                 app = app_factory()
-
-                if isinstance(app, Flask):
-                    return app
+                return app if isinstance(app, Flask) else None
             except TypeError as e:
                 if not _called_with_wrong_args(app_factory):
                     raise
 
-                raise NoAppException(
-                    f"Detected factory '{attr_name}' in module '{module.__name__}',"
-                    " but could not call it without arguments. Use"
-                    f" '{module.__name__}:{attr_name}(args)'"
-                    " to specify arguments."
-                ) from e
+    app = None
+
+    for attr_name in ("app", "application"):
+        app = find_app_by_attribute(attr_name)
+        if isinstance(app, Flask):
+            return app
+
+    app = find_app_by_instance()
+    if app:
+        return app
+
+    for attr_name in ("create_app", "make_app"):
+        app = find_app_by_factory(attr_name)
+        if app:
+            return app
 
     raise NoAppException(
-        "Failed to find Flask application or factory in module"
-        f" '{module.__name__}'. Use '{module.__name__}:name'"
-        " to specify one."
+        f"Failed to find Flask application or factory in module '{module.__name__}'."
+        f" Use '{module.__name__}:name' to specify one."
     )