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explain empty sets

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Mark Pilgrim
2009-07-16 09:09:13 -04:00
parent 68c55d65d5
commit 33e6e053ba
2 changed files with 2 additions and 2 deletions
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native-datatypes.html
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@@ -478,7 +478,7 @@ IndexError: pop from empty list</samp></pre>
<li>The original list is unchanged.
</ol>
<p>Don&#8217;t have any values yet? Not a problem. You can create an empty set.
<p id=emptyset>Don&#8217;t have any values yet? Not a problem. You can create an empty set.
<pre class=screen>
<a><samp class=p>>>> </samp><kbd class=pp>a_set = set()</kbd> <span class=u>&#x2460;</span></a>
porting-code-to-python-3-with-2to3.html
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@@ -1260,7 +1260,7 @@ except:
<h3 id=set_literal><code>set()</code> literals (explicit)</h3>
<p>In Python 2, the only way to define a literal set in your code was to call <code>set(a_sequence)</code>. This still works in Python 3, but a clearer way of doing it is to use the new set literal notation: curly braces. (Dictionaries are also defined with curly braces, which makes sense once you think about it, because dictionaries are just sets of key-value pairs.)
<p>In Python 2, the only way to define a literal set in your code was to call <code>set(a_sequence)</code>. This still works in Python 3, but a clearer way of doing it is to use the new set literal notation: curly braces. This works for everything except empty sets, because dictionaries also use curly braces, so <a href=native-datatypes.html#emptyset><code>{}</code> is an empty dictionary, not an empty set</a>.
<blockquote class=note>
<p><span class=u>&#x261E;</span>The <code>2to3</code> script will not fix <code>set()</code> literals by default. To enable this fix, specify <kbd>-f set_literal</kbd> on the command line when you call <code>2to3</code>.