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pythonadditionletters

Crazy Challenge: Rotating Letters in Python Encipher Function

I'm trying to write a function rot(c,n) that rotates a single character c forward by n spots in the alphabet.

def rot(c,n):
""" rotate c forward by n characters,
    wrapping as needed; only letters change
"""

if 'a' <= c <= 'z':          # lower-case
    new_ord = ord(c) + n
    if new_ord > ord('z'):
        new_ord = new_ord - (2*n)
elif 'A' <= c <= 'Z':        # upper-case
    new_ord = ord(c) + n 
    if new_ord > ord('Z'):
        new_ord = new_ord - (2*n)

else:                        # non-alpha
    new_ord = ord(c)
return chr(new_ord)

However my desired outputs are as follow:

>>> rot('a', 2)
'c'
>>> rot('y', 2)
'a'
>>> rot('A', 3)
'D'
>>> rot('Y', 3)
'B'
>>> rot('!', 4)
'!'

I keep getting the wrong outputs. Can someone tell me what I'm doing wrong?

Solution

  • Your problem is here:

    new_ord = new_ord - (2*n)

    The idea is that when you go past z, you have to remove exactly the whole alphabet and not remove twice what you just added.

    Try:

    new_ord = new_ord - 26