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finished advanced-iterators

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Mark Pilgrim
2009-05-06 23:45:29 -04:00
parent 8e831ca2eb
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@@ -154,21 +154,33 @@ AssertionError</samp></pre>
<h2 id=generator-expressions>Generator expressions</h2>
<p>FIXME
<p>A generator expression is like a <a href=generators.html>generator function</a> without the function.
<pre class=screen>
<samp>>>> </samp><kbd>unique_characters = {'E', 'D', 'M', 'O', 'N', 'S', 'R', 'Y'}</kbd>
<samp>>>> </samp><kbd>gen = (ord(c) for c in unique_characters)</kbd>
<samp>>>> </samp><kbd>gen</kbd>
<a><samp>>>> </samp><kbd>gen = (ord(c) for c in unique_characters)</kbd> <span>&#x2460;</span></a>
<a><samp>>>> </samp><kbd>gen</kbd> <span>&#x2461;</span></a>
<samp>&lt;generator object &lt;genexpr> at 0x00BADC10></samp>
<samp>>>> </samp><kbd>next(gen)</kbd>
<a><samp>>>> </samp><kbd>next(gen)</kbd> <span>&#x2462;</span></a>
<samp>69</samp>
<samp>>>> </samp><kbd>next(gen)</kbd>
<samp>68</samp>
<samp>>>> </samp><kbd>tuple(ord(c) for c in unique_characters)</kbd>
<a><samp>>>> </samp><kbd>tuple(ord(c) for c in unique_characters)</kbd> <span>&#x2463;</span></a>
<samp>(69, 68, 77, 79, 78, 83, 82, 89)</samp></pre>
<ol>
<li>A generator expression is like an anonymous function that yields values. The expression itself looks like a list comprehension [FIXME have we introduced this yet?], but it&#8217;s wrapped in parentheses instead of square brackets.
<li>The generator expression returns&hellip; an iterator.
<li>Calling <code>next(<var>gen</var>)</code> returns the next value from the iterator.
<li>If you like, you can iterate through all the possible values and return a tuple, list, or set, by passing the generator expression to <code>tuple()</code>, <code>list()</code>, or <code>set()</code>.
</ol>
<p>FIXME
<p>Here&#8217;s another way to accomplish the same thing, using a <a href=generators.html>generator function</a>:
<pre><code>def ord_map(a_string):
for c in a_string:
yield ord(c)
gen = ord_map(unique_characters)</code></pre>
<h2 id=permutations>Calculating Permutations&hellip; The Lazy Way!</h2>