How to keep looping until the user input is valid ?

[Yoriz]

In your function get_valid_cable_size you dont need a try except and you are not asking for a value in your loop so it gets stuck in a n infinite loop.
do the following.

1. start a while loop
   
2. call the function get_valid_input to get a value from user input
   
3. check if the value is in acceptable cable sizes
   • if it is return the value
     
   • else tell the user to input a correct value and it will go back to the start of this loop