Python For Kids For Dummies

PROJECT 7

Cryptopy

The muscles you used in the 1337 sp34k3r project get flexed in this project, too. You encrypt and decrypt messages using Python and a little something called a Caesar Cipher.

Julius Caesar was a Roman general. Ciphers are what real-life spies use to make and break codes. A cipher is a procedure or a device that changes readable text (called plaintext) into unreadable text (called ciphertext). Caesar encrypted, or coded, his messages by shifting letters along the alphabet. If he had a plaintext d, he would replace it with an a. For an e he would write b, and so on.

In this project you

• Take a plaintext message.
• Encrypt the message.
• Present the encrypted message.
• Decrypt a ciphertext message into plaintext.
• Present the plaintext.

Your cipher is going to handle uppercase and lowercase letters, plus punctuation marks and numbers. Caesar got off easy. He didn’t have to worry about punctuation or uppercase letters.

Printable characters

How do you get the printable characters? The string module from the standard library includes a list of all of the printable characters as one of its attributes. Type the following to see them:

>>> import string

>>> string.printable

'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c'

 

Everything seems sensible except for the last few. What are all the slashes? These ...