[Tutor] Python help

[Steven D'Aprano]

On Mon, Apr 02, 2018 at 11:44:39PM +0100, Shannon Evans via Tutor wrote:
> Hi, I am trying to write a code with if statements but the code keeps just
> repeating and not carrying on.
> I am trying to get user to input a grade, either A, B, C, D, E or F and
> trying to have an error message if anything but these values are inputted.
> This is what i've wrote so far:
> 
> while True:
>     try:
>         Grade = int(raw_input("Please enter your Grade: "))

Here you convert the user's input into an integer, a number such as 1, 
2, 57, 92746 etc. If that *fails*, you run this block:

>     except ValueError:
>         print("Error, Please enter A, B, C, D, E or F")
>         continue

and start again.

If it succeeds, because the user entered (let's say) 99, then you run 
another test:

>     if Grade <> 'A','B','C','D','E','F':
>         print ("Error, Please enter A, B, C, D, E or F")
>         continue

That will ALWAYS fail, because you are trying to compare the integer 99 
(for example) with the tuple of six characters:

    99 <> ('A', 'B','C','D','E','F')

which is always false. So that block will ALWAYS fail, and you always go 
back to the start.




-- 
Steve