CS circles Coding Exercise: 26 Letters

Question

This coding exercise is giving me a lot of trouble and I need help.

Here is the problem.

Write a program which does the reverse of the example above: it should take a character as input and output the corresponding number (between 1 and 26). Your program should only accept capital letters. As error-checking, print invalid if the input is not a capital letter.

Here is what I have so far.

inp = input()

if (len(inp) > 1 or inp != inp.upper()):
    print("invalid input")

else:
    print(ord(inp)-ord("A")+1)

Answer 1

As clarified in the comment, the problem appears to be that the validation doesn't cover enough cases.

To check that the number you calculate is a valid upper-case character you could just check if it is between 1 and 26:

if 1 < ord(inp) - ord("A") + 1 < 26:
    print(ord(inp) - ord("A") + 1)
else:
    print("Invalid input")

To add this to your current validation:

inp = input()

if (len(inp) > 1 or inp != inp.upper() or 
    ord(inp) - ord("A") + 1 < 1 or ord(inp) - ord("A") + 1 > 26):
    print("invalid input")

else:
    print(ord(inp)-ord("A")+1)