Proper place to get the init data before page rendered

[jixian01]

Hey all,
I want to have a ui page defined in separated python file, and before the page get rendered fetch some data e.g. result from parse big txt file which could be cpu bound operation. I am wondering where is the best place to fetch the data. Some pseudocode to describe the scenario:
option 1: fetch data before @ui.page decorated function and use data inside the function
option2: fetch data inside the @ui.page decorated function
Question:
which option is better and why? or the two options are not properly, there is another better way to do?

Thank you!

#main.py
import my_page.py
from nicegui import ui
ui.run()

#my_page.py

from nicegui import ui

#option 1: fetch data before @ui.page decorator
data = fetchdata() #this could be cpu bound task

@ui.page("/)
def get_page():
#bind and use the data from option 1 with ui component

#option 2: fetch data inside get_page() 
data = fetchdata()
#then bind and use data here

[falkoschindler]

It depends: Does the data change? Then you should fetch it regularly (e.g. using app.timer) or on every page load (option 2). If it doesn't change while the app is running, you can do it once in global scope (option 1).

[jixian01]

thank you for the info!
what is difference between the two options?
option 1 would be executed in backend? option 2 would be executed in browser? and if it is cpu bound task the option 2 will block page rendering?

[falkoschindler]

Option 1 runs once when the app starts.
Option 2 runs whenever a page is requested by a browser.
Both run in the backend.

And yes, CPU-bound tasks would delay the page response and, thus, the rendering. You should create some UI first, await the client connection (which delivers the initial UI and creates a socket connection) and then do the CPU-bound tasks using run.cpu_bound.