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added section on tuples in a boolean context

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Mark Pilgrim
2009-08-04 17:30:24 -07:00
parent 7261bd4349
commit 34c9342b21
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native-datatypes.html
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@@ -499,6 +499,29 @@ AttributeError: 'tuple' object has no attribute 'remove'</samp>
<p><span class=u>&#x261E;</span>Tuples can be converted into lists, and vice-versa. The built-in <code>tuple()</code> function takes a list and returns a tuple with the same elements, and the <code>list()</code> function takes a tuple and returns a list. In effect, <code>tuple()</code> freezes a list, and <code>list()</code> thaws a tuple.
</blockquote>
<h3 id=tuples-in-a-boolean-context>Tuples In A Boolean Context</h3>
<p>You can use tuples 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(())</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 tuple is false.
<li>Any tuple with at least one item is true.
<li>Any tuple with at least one item is true. The value of the items is irrelevant.
</ol>
<h3 id=multivar>Assigning Multiple Values At Once</h3>
<p>Here&#8217;s a cool programming shortcut: in Python, you can use a tuple to assign multiple values at once.