There are three problems with this-
1. the def analyzeWeight function shouldn't return anything, it should print the values. Also you asked the user to enter strings, the numbers do not need quotations usually.
2. the -1 you have in the weight is like an endpoint. It should be under a while loop in your main function.
3. Your 2nd and 3rd elifs, both cases the weight can be equals to 10, python will get confused.
So it would something like this in your main,
1. prompt the user
2. Until the user enters -1, call the analyze function then prompt the user to enter the weight again. When you're calling to the function, it will check and print the appropriate statement.
3. print the last line where you thank the user outside the while loop...