Five-minute starter task

1. Five-minute starter task • Write a function that takes a string argument and returns a spaced out version of the string • E.g. spaceOut("Hello") H e l l o

2. The spaceOut task • You can iterate over a string, like you can a list: • for x in myString: • do something • You cannot change the letters of a string one by one like this: • for x in myString • x = x + ' ' • You have to build up a NEW STRING and then RETURN IT • newStr = "" • for x in myString • newStr = ….

3. Examples of string functions in Python Find full documentation here: http://docs.python.org/3/library/string.html

4. Caesar Ciphers

5. Examples • Plain text:The quick brown fox jumps over the lazy dog • Cipher text:uifrvjdlcspxogpykvnqtpwfsuifmbazeph

6. Clues: You may find these lines of code useful (they are not in order!) • for x in plainText: • # do something with each letter • y = string.ascii_lowercase.find(x) + 1 • cipherText = cipherText + string.ascii_lowercase[y] • plainText = plainText.lower() • You may also find the % operator useful…

7. More clues for every character in plain text: index = number of the character in the alphabet index = index + 1 cipher character = index'th letter of alphabet add cipher character to cipher text This will work in most cases, but you will have a problem when you come across a 'z' and when you come across an upper case letter, and when you come across a space or some punctuation character.

8. Extension tasks • My example only returns cipher text in lower case. Can you write a function that returns mixed cases? • My example will raise an error if the plain text contains punctuation. Can you make your function cope with it? • Write a function that will encrypt txt using ANY rotation. • Write a function that will decrypt anything encrypted using a Caesar cipher.

9. Transposition Ciphers