blocks|key|1866783|text|它是set()的另一种语法|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1866784|>>>+a+=+{1,+2}
>>>+b+=+set()
>>>+b.add(1)
>>>+b.add(2)
>>>+b
set([1,+2])
>>>+a
set([1,+2])
>>>+a+==+b
True
>>>+type(a)+==+type(b)
True|code-block|syntax|javascript|1866785|dict语法不同。它由键-值对组成。例如：|1866786|my_obj+=+{1:None,+2:None}|1866787|entityMap^0|2|5|0|0|0|4|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

It is an alternative syntax for <code>set()</code>

<pre><code>&gt;&gt;&gt; a = {1, 2}
&gt;&gt;&gt; b = set()
&gt;&gt;&gt; b.add(1)
&gt;&gt;&gt; b.add(2)
&gt;&gt;&gt; b
set([1, 2])
&gt;&gt;&gt; a
set([1, 2])
&gt;&gt;&gt; a == b
True
&gt;&gt;&gt; type(a) == type(b)
True
</code></pre>

<code>dict</code> syntax is different. It consists of key-value pairs. For example:

<pre><code>my_obj = {1:None, 2:None}
</code></pre>

blocks|key|1652530|text|Python集合和字典都可以使用大括号构造：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1652531|my_dict+=+{'a':+1,+'b':+2}|offset|length|style|CODE|1652532|my_set+=+{1,+2,+3}|1652533|解释器(和人类读者)可以根据它们的内容来区分它们。然而，不可能区分空集和空字典，所以在这种情况下，您需要对空集使用set()来消除歧义。|1652534|一个非常简单的测试表明，文字构造更快(python3.5)：|1652535|>>>+timeit.timeit('a+=+set([1,+2,+3])')
0.5449375328607857
>>>+timeit.timeit('a+=+{1,+2,+3}')
0.20525191631168127|code-block|syntax|javascript|1652536|This+question涵盖了一些文字构造在内置函数上的性能问题，尽管是针对列表和字典。总结起来，字面结构只需要较少的解释器工作。|1652537|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/30216000/why-is-faster-than-list^0|0|0|Q|0|0|I|0|1L|5|0|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@$D|14|E|15|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|16|8|@$D|17|E|18|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|19|8|@$D|1A|E|1B|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|1C|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|1D|8|@]|9|@]|A|$Q|R]]|$1|S|3|T|5|6|7|1E|8|@]|9|@$D|1F|E|1G|1|1H]]|A|$]]|$1|U|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

Python sets and dictionaries can both be constructed using curly braces:

<code>my_dict = {'a': 1, 'b': 2}</code>

<code>my_set = {1, 2, 3}</code>

The interpreter (and human readers) can distinguish between them based on their contents. However it isn't possible to distinguish between an empty set and an empty dict, so this case you need to use <code>set()</code> for empty sets to disambiguate.

A very simple test suggests that the literal construction is faster (python3.5):

<pre><code>&gt;&gt;&gt; timeit.timeit('a = set([1, 2, 3])')
0.5449375328607857
&gt;&gt;&gt; timeit.timeit('a = {1, 2, 3}')
0.20525191631168127
</code></pre>

<a href="https://stackoverflow.com/questions/30216000/why-is-faster-than-list">This question</a> covers some issues of performance of literal constructions over builtin functions, albeit for lists and dicts. The summary seems to be that literal constructions require less work from the interpreter.

blocks|key|1866835|text|set([iterable])是从可选的可迭代iterable创建集合的构造函数。{}用于创建set+/+dict对象文字。因此，创建的内容取决于您如何使用它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1866836|In+[414]:+x+=+{}

In+[415]:+type(x)
Out[415]:+dict

In+[416]:+x+=+{1}

In+[417]:+type(x)
Out[417]:+set

In+[418]:+x+=+{1:+"hello"}

In+[419]:+type(x)
Out[419]:+dict|code-block|syntax|javascript|1866837|entityMap^0|0|F|N|8|15|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

<code>set([iterable])</code> is the constructor to create a set from the optional iterable <code>iterable</code>. And <code>{}</code> is to create set / dict object literals. So what is created depends on how you use it. 

<pre><code>In [414]: x = {}

In [415]: type(x)
Out[415]: dict

In [416]: x = {1}

In [417]: type(x)
Out[417]: set

In [418]: x = {1: "hello"}

In [419]: type(x)
Out[419]: dict
</code></pre>

In PyCharm, when I write:

<pre><code>return set([(sy + ady, sx + adx)])
</code></pre>

it says "Function call can be replaced with set literal" so it replaces it with:

<pre><code>return {(sy + ady, sx + adx)}
</code></pre>

Why is that? A <code>set()</code> in Python is not the same as a dictionary <code>{}</code>?

And if it wants to optimize this, why is this more effective?

Why is it possible to replace sometimes set() with {}?

解释器

Python

在PyCharm中，当我写道：return set([(sy + ady, sx + adx)])它说“函数调用可以替换为设置文字”，所以它替换为：return {(sy + ady, sx + adx)}为什么会这样呢？Python中的set()与字典{}不同如果它想要优化这一点，为什么这样更有效？

问为什么有时可以用{}替换set()？
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