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Mark Pilgrim
307 lines
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307 lines
11 KiB
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<title>Advanced Iterators - Dive into Python 3</title>
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<p>You are here: <a href=index.html>Home</a> <span>‣</span> <a href=table-of-contents.html#advanced-iterators>Dive Into Python 3</a> <span>‣</span>
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<h1>Iterators <i class=baa>&</i> Generators</h1>
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<blockquote class=q>
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<p><span>❝</span> FIXME <span>❞</span><br>— FIXME
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</blockquote>
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<p id=toc>
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<h2 id=divingin>Diving In</h2>
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<p class=f>FIXME
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<p class=d>[<a href=examples/alphametics.py>download <code>alphametics.py</code></a>]
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<pre><code>import re
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import itertools
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def solve(puzzle):
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words = re.findall('[A-Z]+', puzzle.upper())
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unique_characters = {c for c in ''.join(words)}
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assert len(unique_characters) <= 10
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first_letters = {word[0] for word in words}
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n = len(first_letters)
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sorted_characters = ''.join(first_letters) + \
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''.join(unique_characters - first_letters)
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characters = tuple(ord(c) for c in sorted_characters)
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digits = tuple(ord(c) for c in '0123456789')
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zero = digits[0]
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for guess in itertools.permutations(digits, len(characters)):
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if zero not in guess[:n]:
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equation = puzzle.translate(dict(zip(characters, guess)))
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if eval(equation):
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return equation
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if __name__ == '__main__':
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import sys
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for puzzle in sys.argv[1:]:
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print(puzzle)
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solution = solve(puzzle)
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if solution:
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print(solution)</code></pre>
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<pre class=screen>
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<samp class=p>you@localhost:~$ </samp><kbd>python3 alphametics.py "SEND + MORE == MONEY"</kbd>
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<samp>SEND + MORE == MONEY
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9567 + 1085 == 10652</samp>
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<samp class=p>you@localhost:~$ </samp><kbd>python3 alphametics.py "I + LOVE + YOU == DORA"</kbd>
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<samp>I + LOVE + YOU == DORA
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1 + 2784 + 975 == 3760</samp></pre>
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<h2 id=re-findall>Finding all occurrences of a pattern</h2>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>import re</kbd>
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<samp class=p>>>> </samp><kbd>re.findall('[A-Z]+', 'SEND + MORE == MONEY')</kbd>
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<samp>['SEND', 'MORE', 'MONEY']</samp></pre>
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<p>FIXME
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<h2 id=unique-items>Finding the unique items in a sequence</h2>
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>a_list = ['a', 'c', 'b', 'a', 'd', 'b']</kbd>
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<samp class=p>>>> </samp><kbd>{c for c in a_list}</kbd>
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<samp>{'a', 'c', 'b', 'd'}</samp>
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<samp class=p>>>> </samp><kbd>a_string = 'EAST IS EAST'</kbd>
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<samp class=p>>>> </samp><kbd>{c for c in a_string}</kbd>
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<samp>{'A', ' ', 'E', 'I', 'S', 'T'}</samp>
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<samp class=p>>>> </samp><kbd>words = ['SEND', 'MORE', 'MONEY']</kbd>
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<samp class=p>>>> </samp><kbd>''.join(words)</kbd>
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<samp>'SENDMOREMONEY'</samp>
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<samp class=p>>>> </samp><kbd>{c for c in ''.join(words)}</kbd>
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<samp>{'E', 'D', 'M', 'O', 'N', 'S', 'R', 'Y'}</samp></pre>
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<p>FIXME
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<h2 id=assert>Making assertions</h2>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>assert 1 + 1 = 2</kbd>
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<samp class=p>>>> </samp><kbd>assert 1 + 1 = 3</kbd>
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<samp class=traceback>Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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AssertionError</samp></pre>
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<p>FIXME
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<pre><code>assert len(unique_characters) <= 10</code></pre>
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<p>…is equivalent to…
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<pre><code>if len(unique_characters) > 10:
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raise AssertionError</code></pre>
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<h2 id=generator-objects>Generator objects</h2>
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<p>FIXME
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<pre class=screen>
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<samp>>>> </samp><kbd>unique_characters = {'E', 'D', 'M', 'O', 'N', 'S', 'R', 'Y'}</kbd>
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<samp>>>> </samp><kbd>gen = (ord(c) for c in unique_characters)</kbd>
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<samp>>>> </samp><kbd>gen</kbd>
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<samp><generator object <genexpr> at 0x00BADC10></samp>
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<samp>>>> </samp><kbd>next(gen)</kbd>
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<samp>69</samp>
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<samp>>>> </samp><kbd>next(gen)</kbd>
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<samp>68</samp>
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<samp>>>> </samp><kbd>tuple(ord(c) for c in unique_characters)</kbd>
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<samp>(69, 68, 77, 79, 78, 83, 82, 89)</samp></pre>
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<p>FIXME
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<h2 id=permutations>Calculating Permutations… The Lazy Way!</h2>
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<p>FIXME what are permutations?
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>import itertools</kbd>
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<samp class=p>>>> </samp><kbd>perms = itertools.permutations([1, 2, 3], 2)</kbd>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>(1, 2)</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>(1, 3)</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>(2, 1)</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>(2, 3)</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>(3, 1)</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>(3, 2)</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp class=traceback>Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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StopIteration</samp></pre>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>import itertools</kbd>
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<samp class=p>>>> </samp><kbd>perms = itertools.permutations('ABC', 3)</kbd>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>('A', 'B', 'C')</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>('A', 'C', 'B')</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>('B', 'A', 'C')</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>('B', 'C', 'A')</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>('C', 'A', 'B')</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp>('C', 'B', 'A')</samp>
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<samp class=p>>>> </samp><kbd>next(perms)</kbd>
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<samp class=traceback>Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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StopIteration</samp>
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<samp class=p>>>> </samp><kbd>list(itertools.permutations('ABC', 3))</kbd>
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<samp>[('A', 'B', 'C'), ('A', 'C', 'B'),
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('B', 'A', 'C'), ('B', 'C', 'A'),
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('C', 'A', 'B'), ('C', 'B', 'A')]</samp></pre>
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<p>FIXME
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<h3 id=more-itertools>Other Fun Stuff In The <code>itertools</code> Module</h3>
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>import itertools</kbd>
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<samp class=p>>>> </samp><kbd>list(itertools.product('ABC', '123'))</kbd>
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<samp>[('A', '1'), ('A', '2'), ('A', '3'),
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('B', '1'), ('B', '2'), ('B', '3'),
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('C', '1'), ('C', '2'), ('C', '3')]</samp>
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<samp class=p>>>> </samp><kbd>list(itertools.combinations('ABC', 2))</kbd>
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<samp>[('A', 'B'), ('A', 'C'), ('B', 'C')]</samp></pre>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>names = list(open('examples/favorite-people.txt'))</kbd>
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<samp class=p>>>> </samp><kbd>names</kbd>
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<samp>['Dora\n', 'Ethan\n', 'Wesley\n', 'John\n', 'Anne\n',
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'Mike\n', 'Chris\n', 'Sarah\n', 'Alex\n', 'Lizzie\n']</samp>
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<samp class=p>>>> </samp><kbd>names = [name[:-1] for name in names]</kbd>
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<samp class=p>>>> </samp><kbd>names</kbd>
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<samp>['Dora', 'Ethan', 'Wesley', 'John', 'Anne',
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'Mike', 'Chris', 'Sarah', 'Alex', 'Lizzie']</samp>
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<samp class=p>>>> </samp><kbd>names = sorted(names)</kbd>
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<samp class=p>>>> </samp><kbd>names</kbd>
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<samp>['Alex', 'Anne', 'Chris', 'Dora', 'Ethan',
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'John', 'Lizzie', 'Mike', 'Sarah', 'Wesley']</samp>
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<samp class=p>>>> </samp><kbd>names = sorted(names, key=len)</kbd>
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<samp class=p>>>> </samp><kbd>names</kbd>
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<samp>['Alex', 'Anne', 'Dora', 'John', 'Mike',
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'Chris', 'Ethan', 'Sarah', 'Lizzie', 'Wesley']</samp>
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<samp class=p>>>> </samp><kbd>import itertools</kbd>
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<samp class=p>>>> </samp><kbd>groups = itertools.groupby(names, len)</kbd>
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<samp class=p>>>> </samp><kbd>groups</kbd>
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<samp><itertools.groupby object at 0x00BB20C0></samp>
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<samp class=p>>>> </samp><kbd>list(groups)</kbd>
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<samp>[(4, <itertools._grouper object at 0x00BA8BF0>),
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(5, <itertools._grouper object at 0x00BB4050>),
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(6, <itertools._grouper object at 0x00BB4030>)]</samp>
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<samp class=p>>>> </samp><kbd>groups = itertools.groupby(names, len)</kbd>
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<samp class=p>>>> </samp><kbd>for name_length, name_iter in groups:</kbd>
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<samp class=p>... </samp><kbd> print('Names with {0:d} letters:'.format(name_length))</kbd>
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<samp class=p>... </samp><kbd> for name in name_iter:</kbd>
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<samp class=p>... </samp><kbd> print(name)</kbd>
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<samp class=p>... </samp>
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<samp>Names with 4 letters:
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Alex
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Anne
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Dora
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John
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Mike
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Names with 5 letters:
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Chris
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Ethan
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Sarah
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Names with 6 letters:
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Lizzie
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Wesley</samp></pre>
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<p>FIXME
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<h2 id=zip>Combining Iterators</h2>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>list(range(0, 3))</kbd>
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<samp>[0, 1, 2]</samp>
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<samp class=p>>>> </samp><kbd>list(range(10, 13))</kbd>
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<samp>[10, 11, 12]</samp>
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<samp class=p>>>> </samp><kbd>list(itertools.chain(range(0, 3), range(10, 13)))</kbd>
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<samp>[0, 1, 2, 10, 11, 12]</samp>
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<samp class=p>>>> </samp><kbd>list(zip(range(0, 3), range(10, 13)))</kbd>
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<samp>[(0, 10), (1, 11), (2, 12)]</samp>
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<samp class=p>>>> </samp><kbd>list(zip(range(0, 3), range(10, 14)))</kbd>
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<samp>[(0, 10), (1, 11), (2, 12)]</samp>
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<samp class=p>>>> </samp><kbd>list(itertools.zip_longest(range(0, 3), range(10, 14)))</kbd>
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<samp>[(0, 10), (1, 11), (2, 12), (None, 13)]</samp></pre>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>characters = ('S', 'M', 'E', 'D', 'O', 'N', 'R', 'Y')</kbd>
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<samp class=p>>>> </samp><kbd>guess = ('1', '2', '0', '3', '4', '5', '6', '7')</kbd>
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<samp class=p>>>> </samp><kbd>tuple(zip(characters, guess))</kbd>
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<samp>(('S', '1'), ('M', '2'), ('E', '0'), ('D', '3'),
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('O', '4'), ('N', '5'), ('R', '6'), ('Y', '7'))</samp>
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<samp class=p>>>> </samp><kbd>dict(zip(characters, guess))</kbd>
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<samp>{'E': '0', 'D': '3', 'M': '2', 'O': '4',
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'N': '5', 'S': '1', 'R': '6', 'Y': '7'}</samp></pre>
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<h2 id=new-kind-of-string-manipulation>A New Kind Of String Manipulation</h2>
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>characters = tuple(ord(c) for c in 'SMEDONRY')</kbd>
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<samp class=p>>>> </samp><kbd>characters</kbd>
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<samp>(83, 77, 69, 68, 79, 78, 82, 89)</samp>
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<samp class=p>>>> </samp><kbd>digits = tuple(ord(c) for c in '0123456789')</kbd>
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<samp class=p>>>> </samp><kbd>digits</kbd>
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<samp>(48, 49, 50, 51, 52, 53, 54, 55, 56, 57)</samp>
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<samp class=p>>>> </samp><kbd>guess = (49, 50, 48, 51, 52, 53, 54, 55)</kbd>
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<samp class=p>>>> </samp><kbd>translation_table = dict(zip(characters, guess))</kbd>
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<samp class=p>>>> </samp><kbd>translation_table</kbd>
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<samp>{68: 51, 69: 48, 77: 50, 78: 53, 79: 52, 82: 54, 83: 49, 89: 55}</samp>
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<samp class=p>>>> </samp><kbd>"SEND + MORE == MONEY".translate(translation_table)</kbd>
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<samp>'1053 + 2460 == 24507'</samp></pre>
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<p>FIXME
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<pre class=screen>
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<samp class=p>>>> </samp><kbd>translation_table = {ord("A"): ord("O")}</kbd>
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<samp class=p>>>> </samp><kbd>translation_table</kbd>
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<samp>{65: 79}</samp>
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<samp class=p>>>> </samp><kbd>'MARK'.translate(translation_table)</kbd>
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<samp>'MORK'</samp></pre>
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<p>FIXME
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<h2 id=eval>Evaluating Arbitrary Strings As Python Expressions</h2>
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<p>FIXME
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<h2 id=alphametics-finale>Putting It All Together</h2>
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<p>FIXME
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<h2 id=furtherreading>Further Reading</h2>
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<p>FIXME
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<p class=c>© 2001–9 <a href=about.html><span>ℳ</span>ark Pilgrim</a>
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