X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=slides%2Fcaesar-encipher.html;h=a4d5b2df15bbec0f783b85e6a2d2658314a32742;hb=761cbffc8c433e61da10bd9ccdfed11cb21711dd;hp=4f99cc2e34f4f7f3e364ee1bb457cbe6a2ba24a3;hpb=6f7db403eb131c5f6807cdbd5d4c5d570617fee9;p=cipher-training.git diff --git a/slides/caesar-encipher.html b/slides/caesar-encipher.html index 4f99cc2..a4d5b2d 100644 --- a/slides/caesar-encipher.html +++ b/slides/caesar-encipher.html @@ -5,16 +5,69 @@

-class: center, middle
-
 # Caesar ciphers
 
-* Letter-by-letter enciphering
+![centre-aligned Caesar wheel](caesarwheel1.gif)
+
+Letter-by-letter enciphering
+
+---
+
+# Enciphering and deciphering
+
+## Arithmetic on letters
+
+Convert .plaintext[letter] â .plaintext[number] â 
+.ciphertext[number] â .ciphertext[letter]
+
+Functions you will need
+
+```python
+ord()
+
+chr()
+
+mod()
+```
+
+* What are good test cases?
 
 ---
 
@@ -22,6 +75,7 @@ class: center, middle
 
 ```python
 import string
+
 string.ascii_letters
 string.ascii_lowercase
 string.ascii_uppercase
@@ -29,6 +83,11 @@ string.digits
 string.punctuation
 ```
 
+---
+# DRY and YAGNI
+
+Is your code DRY?
+
 ---
 
 # Doctest
@@ -36,6 +95,43 @@ string.punctuation
 * Why document?
 * Why test?
 
+```python
+def caesar_encipher_letter(letter, shift):
+    """Encipher a letter, given a shift amount
+
+    >>> caesar_encipher_letter('a', 1)
+    'b'
+    """
+    if letter in string.ascii_letters:
+```
+
+---
+
+# My tests
+
+```python
+def caesar_encipher_letter(letter, shift):
+    """Encipher a letter, given a shift amount
+
+    >>> caesar_encipher_letter('a', 1)
+    'b'
+    >>> caesar_encipher_letter('a', 2)
+    'c'
+    >>> caesar_encipher_letter('b', 2)
+    'd'
+    >>> caesar_encipher_letter('x', 2)
+    'z'
+    >>> caesar_encipher_letter('y', 2)
+    'a'
+    >>> caesar_encipher_letter('z', 2)
+    'b'
+    >>> caesar_encipher_letter('z', -1)
+    'y'
+    >>> caesar_encipher_letter('a', -1)
+    'z'
+    """
+    if letter in string.ascii_letters:
+```
 ---
 
 # The magic doctest incantation
@@ -50,6 +146,17 @@ if __name__ == "__main__":
 
 # Doing all the letters
 
+## Test-first developement
+
+1. Write the tests.
+    * They will fail. There is no code.
+2. Write code until the tests pass.
+3. Refactor.
+
+---
+
+# Doing all the letters
+
 ## Abysmal
 
 ```python
@@ -62,7 +169,7 @@ for i in range(len(plaintext)):
 
 # Doing all the letters
 
-## (Merely) Bad
+## Bad
 
 ```python
 ciphertext = ''
@@ -89,7 +196,13 @@ ciphertext = map(lambda p: caesar_encipher_letter(p, key), plaintext)
 ```python
 ciphertext = [caesar_encipher_letter(p, key) for p in plaintext]
 ```
+---
+
+# Not all iterables are equal
 
+```python
+''.join()
+```