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added sets-in-a-boolean-context

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Mark Pilgrim
2009-07-03 23:06:29 -04:00
parent fbd3c859de
commit 5d543d4221
1 changed files with 26 additions and 3 deletions
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native-datatypes.html
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@@ -426,11 +426,11 @@ IndexError: pop from empty list</samp></pre>
<samp class=p>... </samp><kbd class=pp> else:</kbd>
<samp class=p>... </samp><kbd class=pp> print('no, it's false')</kbd>
<samp class=p>...</samp>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true([])</kbd> <span class=u>&#x2461;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true([])</kbd> <span class=u>&#x2460;</span></a>
<samp>no, it's false</samp>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true(['a'])</kbd> <span class=u>&#x2462;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true(['a'])</kbd> <span class=u>&#x2461;</span></a>
<samp>yes, it's true</samp>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true([False])</kbd> <span class=u>&#x2463;</span></a>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true([False])</kbd> <span class=u>&#x2462;</span></a>
<samp>yes, it's true</samp></pre>
<ol>
<li>In a boolean context, an empty list is false.
@@ -650,6 +650,29 @@ KeyError: 21</samp></pre>
<li>
</ol>
<h3 id=sets-in-a-boolean-context>Sets In A Boolean Context</h3>
<p>You can use sets in <a href=#booleans>a boolean context</a>, such as an <code>if</code> statement.
<pre class=screen>
<samp class=p>>>> </samp><kbd class=pp>def is_it_true(anything):</kbd>
<samp class=p>... </samp><kbd class=pp> if anything:</kbd>
<samp class=p>... </samp><kbd class=pp> print('yes, it's true')</kbd>
<samp class=p>... </samp><kbd class=pp> else:</kbd>
<samp class=p>... </samp><kbd class=pp> print('no, it's false')</kbd>
<samp class=p>...</samp>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true(set())</kbd> <span class=u>&#x2460;</span></a>
<samp>no, it's false</samp>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true({'a'})</kbd> <span class=u>&#x2461;</span></a>
<samp>yes, it's true</samp>
<a><samp class=p>>>> </samp><kbd class=pp>is_it_true({False})</kbd> <span class=u>&#x2462;</span></a>
<samp>yes, it's true</samp></pre>
<ol>
<li>In a boolean context, an empty set is false.
<li>Any set with at least one item is true.
<li>Any set with at least one item is true. The value of the items is irrelevant.
</ol>
<p class=a>&#x2042;
<h2 id=dictionaries>Dictionaries</h2>