1. String
X=“Python Rocks!”
X.index(“O”)

2. Character Encoding ASCII code
A – 65; B – 66; … ; Z – 90
>>> ord(‘A’) # ASCII value or order of letter
>>> chr(65) # opposite of ord()

3. Cryptography
Encoding and Decoding Messages

4. Translation Cipher Replace each character by ord(character)+constant
A B C D E F …. X Y Z … …
26 or over -> wrap around

5. EncoderDecoder.py (p.99)
message = input(“Enter a message to encode: \n”)
message = message.upper() # make all uppercase
cipher = “”
for letter in message:
if letter.isupper():
val = ord(letter)+13
newlet = chr(val)
if not newlet.isupper():
newlet = chr(val-26)
cipher = cipher + newlet
print(“Cipher text: “, cipher)

6. Update with Modulo Function
EncoderDecoder.py
Update with Modulo Function
message = input(“Enter a message to encode: \n”)
message = message.upper()
cipher = “”
for letter in message:
if letter.isupper():
val = ord(letter)+13
newlet = chr(val)
if not newlet.isupper():
newlet = chr(val-26)
cipher = cipher + newlet
print(“Cipher text: “, cipher)
message = input(“Enter a message to encode: \n”)
message = message.upper()
cipher = “”
for letter in message:
cipher = cipher + newlet
print(“Cipher text: “, cipher)

7. Encryption Key

8. Vigenere Square

9. A Card Game Computer draws a card for me and one for you
Wins whichever has a higher face value

10. HighCard.py (p. 125) import random
faces = [“two”,”three”,”four”,”five”,”six”,”seven”,”eight”,”nine”,”ten”,”jack”,”queen”,”kin g”,”ace”]
keep_going=1
while keep_going>0:
my_face = random.choice(faces)
your_face = random.choice(faces)
if faces.index(my_face) > faces.index(your_face):
print (“I win!”)
elif faces.index(my_face)<faces.index(your_face):
print(“You win!”)
else:
print(“A tie!”)
keep_going=eval(input(“Enter 0 to stop, 1 to continue”))

11. HW 3 Due next Wed (10/14) 10:00 AM Do two problems
Chap. 5 #2: User-defined keys (p. 102)
Instead of constant 13 to translate, use a number a user enters in the keyboard
Use the modulo operator to replace a letter by a cipher letter
Chap. 6 #3: War
two programs to