Add code used in presentation

Author: gjbex

source_code/presentation/operators-functools/README.md

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+OperatorsFunctools
+==================
+
+Python has a number of packages that are useful for functional style
+programming, some of these are illustrated here.
+
+What is it?
+-----------
+1. `sort.py`: illustrates sorting a list of nested tuples using a lambda
+    function, and `operator`'s `itemgetter` higher order function.
+1. `reduce.py`: illustrates `functools`'s `reduce` function by computing
+    the factorial function.

source_code/presentation/operators-functools/reduce.py

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+#!/usr/bin/env python
+
+import functools
+import operator
+
+if __name__ == '__main__':
+    for i in range(0, 11):
+        print(i, functools.reduce(operator.mul, range(1, i + 1), 1))

source_code/presentation/operators-functools/sort.py

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+#!/usr/bin/env python
+
+from operator import itemgetter
+
+data = [
+    ('c', (19, 1)),
+    ('b', (12, 2)),
+    ('d', (13, 4)),
+    ('a', (17, 3)),
+]
+
+
+def print_data(msg, data):
+    print(msg)
+    data_str = '\t' + '\n\t'.join([str(x) for x in data])
+    print(data_str)
+
+if __name__ == '__main__':
+    print_data('original list', data)
+    sorted_data = sorted(data, key=lambda x: x[1][0])
+    print_data('lambda sort', sorted_data)
+    sorted_data = sorted(data, key=itemgetter(1, 0))
+    print_data('itemgetter sort', sorted_data)