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quoting attribute values is a hard habit to break

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Mark Pilgrim
2009-05-20 17:34:24 -04:00
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@@ -184,7 +184,7 @@ gen = ord_map(unique_characters)</code></pre>
<h2 id=permutations>Calculating Permutations&hellip; The Lazy Way!</h2>
<p>First of all, what the heck are permutations? Permutations are a mathematical concept. (There are actually several definitions, depending on what kind of math you&#8217;re doing. Here I&#8217;m talking about combinatorics, but if that doesn&#8217;t mean anything to you, don&#8217;t worry about it. As always, <a href="http://en.wikipedia.org/wiki/Permutation">Wikipedia is your friend</a>.)
<p>First of all, what the heck are permutations? Permutations are a mathematical concept. (There are actually several definitions, depending on what kind of math you&#8217;re doing. Here I&#8217;m talking about combinatorics, but if that doesn&#8217;t mean anything to you, don&#8217;t worry about it. As always, <a href=http://en.wikipedia.org/wiki/Permutation>Wikipedia is your friend</a>.)
<p>The idea is that you take a list of things (could be numbers, could be letters, could be dancing bears) and find all the possible ways to split them up into smaller lists. All the smaller lists have the same size, which can be as small as 1 and as large as the total number of items. Oh, and nothing can be repeated. Mathematicians say things like &#8220;let&#8217;s find the permutations of 3 different items taken 2 at a time,&#8221; which means you have a sequence of 3 items and you want to find all the possible ordered pairs.
@@ -559,11 +559,11 @@ NameError: name '__import__' is not defined</samp></pre>
<h2 id=furtherreading>Further Reading</h2>
<ul>
<li><a href="http://blip.tv/file/1947373/">Watch Raymond Hettinger&#8217;s "Easy AI with Python" talk</a> at PyCon 2009
<li><a href="http://code.activestate.com/recipes/576615/">Recipe 576615: Alphametics solver</a>, Raymond Hettinger&#8217;s original alphametics solver for Python 2
<li><a href="http://code.activestate.com/recipes/users/178123/">More of Raymond Hettinger&#8217;s recipes</a> in the ActiveState Code repository
<li><a href="http://en.wikipedia.org/wiki/Verbal_arithmetic">Alphametics on Wikipedia</a>
<li><a href="http://www.tkcs-collins.com/truman/alphamet/index.shtml">Alphametics Index</a>, including <a href="http://www.tkcs-collins.com/truman/alphamet/alphamet.shtml">lots of puzzles</a> and <a href="http://www.tkcs-collins.com/truman/alphamet/alpha_gen.shtml">a generator to make your own</a>
<li><a href=http://blip.tv/file/1947373/>Watch Raymond Hettinger&#8217;s &#8220;Easy AI with Python&#8221; talk</a> at PyCon 2009
<li><a href=http://code.activestate.com/recipes/576615/>Recipe 576615: Alphametics solver</a>, Raymond Hettinger&#8217;s original alphametics solver for Python 2
<li><a href=http://code.activestate.com/recipes/users/178123/>More of Raymond Hettinger&#8217;s recipes</a> in the ActiveState Code repository
<li><a href=http://en.wikipedia.org/wiki/Verbal_arithmetic>Alphametics on Wikipedia</a>
<li><a href=http://www.tkcs-collins.com/truman/alphamet/index.shtml>Alphametics Index</a>, including <a href="ttp://www.tkcs-collins.com/truman/alphamet/alphamet.shtml>lots of puzzles</a> and <a href=http://www.tkcs-collins.com/truman/alphamet/alpha_gen.shtml>a generator to make your own</a>
</ul>
<p>Many, many thanks to Raymond Hettinger for agreeing to relicense his code so I could port it to Python 3 and use it as the basis for this chapter.