Naming Variables

Question

I can't understand what goes wrong with the variable [ user_id ]. Isn't user_id is a valid variable? To me it's valid because it doesn't start with NUMBER, doesn't include any SPACE or any other invalid characters I know. But system is showing it as an invalid variable. Please make me understand. Oh, third brackets are used just to highlight.

Answer 1

Can you share your code as per this guide? Maybe there's something else.

https://sololearn.com/compiler-playground/Wek0V1MyIR2r/?ref=app

Answer 2

I can't share that code as it was from LEARN PYTHON in this Sololearn. Also as I am not a pro user, I couldn't check that explanation of the mistake. Thank you for your will to help.