update get_app doc

Author: LiamConnors

dash/_get_app.py

@@ -39,6 +39,13 @@ def wrap(*args, **kwargs):
 
 
 def get_app():
+ """
+ Return the current Dash app instance.
+
+ Useful in multi-page apps when Python files within the `pages/` folder
+ need to reference the `app` object but importing it directly would cause
+ a circular import error.
+ """
  try:
  ctx_app = app_context.get()
  if ctx_app is not None: