<!DOCTYPE html>
<html>
<head>
- <title>Title</title>
+ <title>Caesar cipher</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<style type="text/css">
/* Slideshow styles */
font-weight: 400;
margin-bottom: 0;
}
- h1 { font-size: 4em; }
+ h1 { font-size: 3em; }
h2 { font-size: 2em; }
h3 { font-size: 1.6em; }
a, a > code {
- /* color: rgb(249, 38, 114); */
text-decoration: none;
}
code {
border-radius: 5px;
font-size: 16px;
}
+ .plaintext {
+ background: #272822;
+ color: #80ff80;
+ text-shadow: 0 0 20px #333;
+ padding: 2px 5px;
+ }
+ .ciphertext {
+ background: #272822;
+ color: #ff6666;
+ text-shadow: 0 0 20px #333;
+ padding: 2px 5px;
+ }
</style>
</head>
<body>
-* Letter-by-letter enciphering
+Letter-by-letter enciphering
+
+---
+
+# Enciphering and deciphering
+
+## Arithmetic on letters
+
+Convert .plaintext[letter] → .plaintext[number] →
+.ciphertext[number] → .ciphertext[letter]
+
+Functions you will need
+
+```python
+ord()
+
+chr()
+
+%
+```
+
+* What are good test cases?
---
```python
import string
+
string.ascii_letters
string.ascii_lowercase
string.ascii_uppercase
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
---
+# Accents
+
+```python
+>>> caesar_encipher_letter('é', 1)
+```
+What does it produce?
+
+What should it produce?
+
+## Unicode, combining codepoints, and normal forms
+
+Text encodings will bite you when you least expect it.
+
+* urlencoding is the other pain point.
+
+---
+
+# Five minutes on StackOverflow later...
+
+```python
+def unaccent(text):
+ """Remove all accents from letters.
+ It does this by converting the unicode string to decomposed compatibility
+ form, dropping all the combining accents, then re-encoding the bytes.
+
+ >>> unaccent('hello')
+ 'hello'
+ >>> unaccent('HELLO')
+ 'HELLO'
+ >>> unaccent('héllo')
+ 'hello'
+ >>> unaccent('héllö')
+ 'hello'
+ >>> unaccent('HÉLLÖ')
+ 'HELLO'
+ """
+ return unicodedata.normalize('NFKD', text).\
+ encode('ascii', 'ignore').\
+ decode('utf-8')
+```
+
+---
+
+# 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
# Doing all the letters
-## (Merely) Bad
+## Bad
```python
ciphertext = ''
ciphertext += caesar_encipher_letter(p, key)
```
+...but easily generalisable
+
---
# Doing all the letters
## Good (but unPythonic)
```python
-ciphertext = map(lambda p: caesar_encipher_letter(p, key),
- plaintext)
+ciphertext = map(lambda p: caesar_encipher_letter(p, key), plaintext)
```
---
## Best
```python
-ciphertext = [caesar_encipher_letter(p, key)
- for p in plaintext]
+ciphertext = [caesar_encipher_letter(p, key) for p in plaintext]
```
+---
+# Not all iterables are equal
+
+```python
+''.join()
+```
</textarea>
<script src="http://gnab.github.io/remark/downloads/remark-0.6.0.min.js" type="text/javascript">
</script>
<script type="text/javascript">
- var slideshow = remark.create();
+ var slideshow = remark.create({ ratio: "16:9" });
</script>
</body>
</html>
\ No newline at end of file
projects / cipher-training.git / blobdiff