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+ <head>
+ <title>Affine ciphers</title>
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+ .ciphertext {
+ background: #272822;
+ color: #ff6666;
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+
+# Breaking keyword ciphers
+
+a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z
+--|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|--
+k | e | y | w | o | r | d | a | b | c | f | g | h | i | j | l | m | n | p | q | s | t | u | v | x | z
+
+----
+
+# Duplicate and extend your `affine_break()` function
+
+* How to cycle through all the keys? What _are_ all the keys?
+
+* Look at `words.txt`
+
+---
+
+# Test it.
+
+* `2013/4a.ciphertext`
+* `2013/4b.ciphertext`
+
+This will take a while. Fire up a system monitor. What's wrong?
+
+---
+
+# Python, threads, and the GIL
+
+Thread-safe shared-memory code is hard.
+
+Python's Global Interpreter Lock prevents shooting yourself in the foot.
+
+Where you want true parallelism, need different threads (Python processes).
+* Thread-safe shared-memory code is hard.
+
+The `multiprocessing` library makes this easier.
+
+But before we get there, a couple of diversions...
+
+---
+
+# `map()`
+
+A common task is to apply a function to each item in a sequence, returning a sequence of the results.
+
+```python```
+def double(x):
+ return x * 2
+
+>>> map(double, [1,2,3])
+[2,4,6]
+```
+
+* `map()` is a higher-order function: its first argument is the function that's applied.
+
+How can we use this for keyword cipher breaking?
+
+---
+
+# Mapping keyword decipherings
+
+Define a function that takes a possible key (keyword and cipher type) and returns the key and its fitness.
+
+Use `map()` and `max()` to find the best key
+
+---
+
+# `print()`
+
+How many arguments does this take?
+
+How do you write a function that takes this many arguments?
+
+---
+
+# Function arguments
+
+## Positional, keyword
+
+* Common or garden parameters, as you're used to.
+* `def keyword_encipher(message, keyword, wrap_alphabet=0):`
+
+## Excess positional
+* `def mean(x, *xs):`
+
+First number goes in `x`, remaining go in the tuple `xs`
+
+## Excess keyword
+
+* `def myfunc(arg1=0, **kwargs):`
+
+`kwargs` will be a Dict of the remaining keywords (not `arg1`)
+
+---
+
+# Back to `multiprocessing`
+
+What does `Pool.starmap()` do?
+
+ </textarea>
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