Title

X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=slides%2Fcaesar-encipher.html;h=4afd78dad4f3367c5107a99d0f40ff8f1e0aa037;hb=7203ac94911556e2b4bf4caab6f5285445faed3b;hp=4f99cc2e34f4f7f3e364ee1bb457cbe6a2ba24a3;hpb=6f7db403eb131c5f6807cdbd5d4c5d570617fee9;p=cipher-training.git diff --git a/slides/caesar-encipher.html b/slides/caesar-encipher.html index 4f99cc2..4afd78d 100644 --- a/slides/caesar-encipher.html +++ b/slides/caesar-encipher.html @@ -1,20 +1,112 @@ - Title + Caesar cipher

-class: center, middle
-
 # Caesar ciphers
 
-* Letter-by-letter enciphering
+![centre-aligned Caesar wheel](caesarwheel1.gif)
+
+Letter-by-letter enciphering
+
+---
+
+layout: true
+
+.indexlink[[Index](index.html)]
+
+---
+
+# 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()
+
+%
+```
+
+* What are good test cases?
+
+---
+
+# Using the tools
+
+Before doing anything, create a new branch in Git
+
+* This will keep your changes isolated
+
+Experiment in IPython (ephemeral, for us)
+
+Once you've got something working, copy the code into a `.py` file (permanent and reusable)
+
+```python
+from imp import reload
+
+import test
+reload(test)
+from test import *
+```
+
+Re-evaluate the second cell to reload the file into the IPython notebook
+
+When you've made progress, make a Git commit
+
+* Commit early and often!
+
+When you've finished, change back to `master` branch and `merge` the development branch
 
 ---
 
@@ -22,6 +114,7 @@ class: center, middle
 
 ```python
 import string
+
 string.ascii_letters
 string.ascii_lowercase
 string.ascii_uppercase
@@ -31,11 +124,30 @@ string.punctuation
 
 ---
 
+# DRY and YAGNI
+
+Is your code DRY?
+
+---
+
 # Doctest
 
 * 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:
+    .
+    .
+    .
+```
+
 ---
 
 # The magic doctest incantation
@@ -48,7 +160,18 @@ if __name__ == "__main__":
 
 ---
 
-# Doing all the letters
+# Doing the whole message
+
+## Test-first developement
+
+1. Write the tests.
+    * They will fail. There is no code.
+2. Write code until the tests pass.
+3. Refactor.
+
+---
+
+# Doing the whole message
 
 ## Abysmal
 
@@ -58,11 +181,13 @@ for i in range(len(plaintext)):
     ciphertext += caesar_encipher_letter(plaintext[i], key)
 ```
 
+Try it in IPython
+
 ---
 
-# Doing all the letters
+# Doing the whole message
 
-## (Merely) Bad
+## Bad
 
 ```python
 ciphertext = ''
@@ -70,9 +195,11 @@ for p in plaintext:
     ciphertext += caesar_encipher_letter(p, key)
 ```
 
+...but easily generalisable
+
 ---
 
-# Doing all the letters
+# Doing the whole message
 
 ## Good (but unPythonic)
 
@@ -82,20 +209,26 @@ ciphertext = map(lambda p: caesar_encipher_letter(p, key), plaintext)
 
 ---
 
-# Doing all the letters
+# Doing the whole message
 
 ## Best
 
 ```python
 ciphertext = [caesar_encipher_letter(p, key) for p in plaintext]
 ```
+---
 
+# Not all iterables are equal
+
+```python
+''.join()
+```

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