Python / Language / Strings

cypher.py

# A Caesar cypher is a weak form on encryption
# It involves "rotating" each letter by a number (shift it through the alphabet)
# A rotated by 3 is D; Z rotated by 1 is A
# In a SF movie the computer is called HAL, which is IBM rotated by -1

# Write a function rotate_word()
# Use built-in functions ord (char to code_number), chr (codes to char)

# SOLUTION

def rotate(word, no):
    rotated = ""
    for i in range(len(word)):
        char = ord(word[i]) + no
        new = chr(char)
        rotated = rotated + new
    return rotated

print(rotate("abc", 1))  # bcd 
print(rotate("abc", 3))  # def 
print(rotate("IBM", -1))  # HAL 
print(rotate("HAL", 1))  # IBM
print(rotate("Hello World", 13))  # Uryy|-d|yq



# EXTRA - DECRYPT (without cypher)

def decrypt(word, no):
    return rotate(word, -no)

for i in range(26):
    print(decrypt("Uryy|-d|yq", i))

"""
...
Jgnnq"Yqnf
Ifmmp!Xpme
Hello Wold
GdkknVnkc
...
"""