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POPython - Access a class from a list using a key
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  1. POPython - Access a class from a list using a key
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    copied!<p>Is there any way to make a list of classes behave like a set in python?</p> <p>Basically, I'm working on a piece of software that does some involved string comparison, and I have a custom class for handling the strings. Therefore, there is an instance of the class for each string.</p> <p>As a result, I have a large list containing all these classes. I would like to be able to access them like <code>list[key]</code>, where in this case, the key is a string the class is based off of (note: the string will never change once the class is instantiated, so it should be hashable).</p> <p>It seems to me that I should be able to do this somewhat easily, by adding something like <code>__cmp__</code> to the class, but either I'm being obtuse (likely), or I'm missing something in the docs.</p> <p>Basically, I want to be able to do something like this (Python prompt example):</p> <pre><code>&gt;&gt;class a: ... def __init__(self, x): ... self.var = x ... &gt;&gt;&gt; from test import a &gt;&gt;&gt; cl = set([a("Hello"), a("World"), a("Pie")]) &gt;&gt;&gt; print cl set([&lt;test.a instance at 0x00C866C0&gt;, &lt;test.a instance at 0x00C866E8&gt;, &lt;test.a instance at 0x00C86710&gt;]) &gt;&gt;&gt; cl["World"] &lt;test.a instance at 0x00C866E8&gt; </code></pre> <p>Thanks!</p> <p><em>Edit</em> Some additional Tweaks:</p> <pre><code>class a: ... def __init__(self, x): ... self.var = x ... def __hash__(self): ... return hash(self.var) ... &gt;&gt;&gt; v = a("Hello") &gt;&gt;&gt; x = {} &gt;&gt;&gt; x[v]=v &gt;&gt;&gt; x["Hello"] Traceback (most recent call last): File "&lt;stdin&gt;", line 1, in &lt;module&gt; KeyError: 'Hello' &gt;&gt;&gt; x["Hello"] </code></pre>
 

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