Merge lp:~brunogirin/python-snippets/sets101 into lp:~jonobacon/python-snippets/trunk

[Bruno Girin]

Added snippet that demonstrates set operators (union, intersection, etc).

Unmerged revisions

100. By Bruno Girin on 2010-05-03

Added snippets to demonstrate set operators.

=== added file 'pythoncore/sets101.py'
--- pythoncore/sets101.py	1970-01-01 00:00:00 +0000
+++ pythoncore/sets101.py	2010-05-03 20:20:51 +0000
@@ -0,0 +1,93 @@
+#!/usr/bin/env python
+#
+# [SNIPPET_NAME: Sets 101]
+# [SNIPPET_CATEGORIES: Python Core]
+# [SNIPPET_DESCRIPTION: Basic and not so basic set operations]
+# [SNIPPET_AUTHOR: Bruno Girin <[e-mail]>]
+# [SNIPPET_LICENSE: GPL]
+
+# This snippet demonstrates how the basics on sets: how to create sets, add,
+# remove items, and use set operations.
+# The set operators demonstrated in this snippet are courtesy of a very good
+# article by Carl Chenet in the April 2010 French edition of Linux Magazine.
+
+#
+# First, let's create simple list. A list is an ordered collection of items
+# and can have duplicates.
+#
+print "Create a simple list"
+simpleList = ["Karmic", "Lucid", "Hardy", "Jaunty", "Intrepid", "Lucid"]
+# print it
+print simpleList
+# 
+# Create a set from the list. A set is an un-ordered collection of items and
+# cannot have duplicates. So creating a set from a list is a quick way to
+# remove any duplicates. However, you lose the ordering when you do that.
+#
+simpleSet = set(simpleList)
+# print it
+print simpleSet
+# order it based on the natural ordering of the elements and print it
+print sorted(simpleSet)
+#
+# Interrogate the set
+#
+print "\nInterrogate the set"
+# get the length of the set
+print "Number of items in the set: ", len(simpleSet)
+# is Maverick in the set?
+print "Maverick is in the set:", ("Maverick" in simpleSet)
+# iterate over the set
+print "\nIterate over the set"
+for v in simpleSet:
+    print v
+#
+# Modify the set
+#
+print "\nModify the set"
+# add another item
+simpleSet.add("Maverick")
+print simpleSet
+# remove an item
+simpleSet.remove("Intrepid")
+print simpleSet
+#
+# Set operators
+# In the code below, all sets are sorted when printed to make it easier to show
+# what the operators do but you don't have to do this in actual code.
+#
+print "\nSet operators"
+# create two sets
+lts = set(["Dapper", "Hardy", "Lucid"])
+recent = set(["Hardy", "Intrepid", "Jaunty", "Karmic", "Lucid"])
+print "LTS:", sorted(lts)
+print "Recent:", sorted(recent)
+# set union
+union = lts | recent
+print sorted(union)
+# set intersection
+inter = lts & recent
+print sorted(inter)
+# symetrical difference (items in either set but not both)
+sym = lts ^ recent
+print sorted(sym)
+# difference
+diff = recent - lts
+print sorted(diff)
+# the operators above also have versions to update in the set in place
+print "\nIn place set operators"
+latest = set(["Karmic", "Lucid", "Maverick"])
+print "Latest:", sorted(latest)
+# union
+union |= latest
+print sorted(union)
+# intersection
+inter &= latest
+print sorted(inter)
+# symetrical difference
+sym ^= latest
+print sorted(sym)
+# difference
+diff -= latest
+print sorted(diff)
+