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changed alphametics to use set() instead of set comprehensions, which neatly dovetails with my irrational reluctance to explain comprehensions

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This commit is contained in:
Mark Pilgrim
2009-07-15 09:54:39 -04:00
parent f14715ed37
commit 2193602838
3 changed files with 11 additions and 10 deletions
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advanced-iterators.html
+9 -9
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@@ -50,7 +50,7 @@ import itertools
def solve(puzzle):
words = re.findall('[A-Z]+', puzzle.upper())
unique_characters = {c for c in ''.join(words)}
unique_characters = set(join(words))
assert len(unique_characters) <= 10
first_letters = {word[0] for word in words}
n = len(first_letters)
@@ -127,30 +127,30 @@ if __name__ == '__main__':
<h2 id=unique-items>Finding the unique items in a sequence</h2>
<p>Set comprehensions make it trivial to find the unique items in a sequence. [FIXME-not sure if I&#8217;m going to cover set comprehensions in an earlier chapter; if not, this is certainly an abrupt and inadequate introduction to the topic.]
<p><a href=native-datatypes.html#sets>Sets</a> make it trivial to find the unique items in a sequence.
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>a_list = ['a', 'c', 'b', 'a', 'd', 'b']</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>{c for c in a_list}</kbd> <span class=u>&#x2460;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>set(a_list)</kbd> <span class=u>&#x2460;</span></a>
<samp class=pp>{'a', 'c', 'b', 'd'}</samp>
<samp class=p>>>> </samp><kbd class=pp>a_string = 'EAST IS EAST'</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>{c for c in a_string}</kbd> <span class=u>&#x2461;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>set(a_string)</kbd> <span class=u>&#x2461;</span></a>
<samp class=pp>{'A', ' ', 'E', 'I', 'S', 'T'}</samp>
<samp class=p>>>> </samp><kbd class=pp>words = ['SEND', 'MORE', 'MONEY']</kbd>
<a><samp class=p>>>> </samp><kbd class=pp>''.join(words)</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>''.join(words)</kbd> <span class=u>&#x2462;</span></a>
<samp class=pp>'SENDMOREMONEY'</samp>
<a><samp class=p>>>> </samp><kbd class=pp>{c for c in ''.join(words)}</kbd> <span class=u>&#x2463;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>set(''.join(words))</kbd> <span class=u>&#x2463;</span></a>
<samp class=pp>{'E', 'D', 'M', 'O', 'N', 'S', 'R', 'Y'}</samp></pre>
<ol>
<li>Given a list of several strings, a set comprehension with the identity function will return a set of unique strings from the list. This makes sense if you think of it like a <code>for</code> loop. Take the first item from the list, put it in the set. Second. Third. Fourth&nbsp;&mdash;&nbsp;wait, that&#8217;s in the set already, so it only gets listed once. Fifth. Sixth&nbsp;&mdash;&nbsp;again, a duplicate, so it only gets listed once. The end result? All the unique items in the original list, without any duplicates. The original list doesn&#8217;t even need to be sorted first.
<li>Given a list of several strings, the <code>set()</code> function will return a set of unique strings from the list. This makes sense if you think of it like a <code>for</code> loop. Take the first item from the list, put it in the set. Second. Third. Fourth&nbsp;&mdash;&nbsp;wait, that&#8217;s in the set already, so it only gets listed once, because Python sets don&#8217;t allow duplicates. Fifth. Sixth&nbsp;&mdash;&nbsp;again, a duplicate, so it only gets listed once. The end result? All the unique items in the original list, without any duplicates. The original list doesn&#8217;t even need to be sorted first.
<li>The same technique works with strings, since a string is just a sequence of characters.
<li>Given a list of strings, <code>''.join(<var>a_list</var>)</code> concatenates all the strings together into one.
<li>So, given a list of strings, this set comprehension returns all the unique characters across all the strings, with no duplicates.
<li>So, given a list of strings, this line of code returns all the unique characters across all the strings, with no duplicates.
</ol>
<p>The alphametics solver uses this technique to get a list of all the unique characters in the puzzle.
<pre class=nd><code class=pp>unique_characters = {c for c in ''.join(words)}</code></pre>
<pre class=nd><code class=pp>unique_characters = set(''.join(words))</code></pre>
<p>This list is later used to assign digits to characters as the solver iterates through the possible solutions.
diveintopython3.org
+1
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@@ -7,6 +7,7 @@
* Closures & Generators
* Classes & Iterators
* TODO 2nd draft Advanced Iterators
SCHEDULED: <2009-07-15 Wed>
* TODO 2nd draft Unit Testing
* TODO 1st draft Advanced Unit Testing
* TODO 2nd draft Refactoring
examples/alphametics.py
Regular → Executable
+1 -1
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@@ -9,7 +9,7 @@ import itertools
def solve(puzzle):
words = re.findall('[A-Z]+', puzzle.upper())
unique_characters = {c for c in ''.join(words)}
unique_characters = set(''.join(words))
assert len(unique_characters) <= 10
first_letters = {word[0] for word in words}
n = len(first_letters)