blocks|key|1418822|text|有一个ordered+set+(可能的new+link)配方，可以从Python+2+Documentation中引用。它可以在Py2.6或更高版本以及3.0或更高版本上运行，无需任何修改。该接口几乎与普通集合完全相同，只是初始化应使用列表完成。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1418823|OrderedSet([1,+2,+3])|code-block|syntax|javascript|1418824|这是一个MutableSet，所以.union的签名与set的签名不匹配，但是因为它包含__or__，所以可以很容易地添加一些类似的东西：|style|CODE|1418825|@staticmethod
def+union(*sets):
++++union+=+OrderedSet()
++++union.union(*sets)
++++return+union

def+union(self,+*sets):
++++for+set+in+sets:
++++++++self+%7C=+set|1418826|entityMap|0|LINK|mutability|MUTABLE|url|http://code.activestate.com/recipes/576694/|1|https://github.com/ActiveState/code/blob/3b27230f418b714bc9a0f897cb8ea189c3515e99/recipes/Python/576696_OrderedSet_with_Weakrefs/README.md|2|https://docs.python.org/2/library/collections.html^0|3|B|0|J|8|1|Y|M|2|0|0|H|6|18|6|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]|$A|14|B|15|1|16]|$A|17|B|18|1|19]]|C|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1B|8|@$A|1C|B|1D|K|L]|$A|1E|B|1F|K|L]]|9|@]|C|$]]|$1|M|3|N|5|F|7|1G|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|1H|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]|Y|$5|R|S|T|C|$U|Z]]]]

There is an <a href="http://code.activestate.com/recipes/576694/" rel="noreferrer">ordered set</a> (possible <a href="https://github.com/ActiveState/code/blob/3b27230f418b714bc9a0f897cb8ea189c3515e99/recipes/Python/576696_OrderedSet_with_Weakrefs/README.md" rel="noreferrer">new link</a>) recipe for this which is referred to from the <a href="https://docs.python.org/2/library/collections.html" rel="noreferrer">Python 2 Documentation</a>. This runs on Py2.6 or later and 3.0 or later without any modifications. The interface is almost exactly the same as a normal set, except that initialisation should be done with a list.

<pre><code>OrderedSet([1, 2, 3])
</code></pre>

This is a MutableSet, so the signature for <code>.union</code> doesn't match that of set, but since it includes <code>__or__</code> something similar can easily be added:

<pre><code>@staticmethod
def union(*sets):
 union = OrderedSet()
 union.union(*sets)
 return union

def union(self, *sets):
 for set in sets:
 self |= set
</code></pre>

blocks|key|1418895|text|对于许多目的，只需调用sorted就足够了。例如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1418896|>>>+s+=+set([0,+1,+2,+99,+4,+40,+3,+20,+24,+100,+60])
>>>+sorted(s)
[0,+1,+2,+3,+4,+20,+24,+40,+60,+99,+100]|code-block|syntax|javascript|1418897|如果你打算重复使用它，调用排序函数会产生开销，所以你可能想要保存结果列表，只要你完成了集合的更改。如果您需要维护惟一的元素并进行排序，我同意从具有任意值的集合中使用OrderedDict的建议。|1418898|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For many purposes simply calling sorted will suffice. For example

<pre><code>&gt;&gt;&gt; s = set([0, 1, 2, 99, 4, 40, 3, 20, 24, 100, 60])
&gt;&gt;&gt; sorted(s)
[0, 1, 2, 3, 4, 20, 24, 40, 60, 99, 100]
</code></pre>

If you are going to use this repeatedly, there will be overhead incurred by calling the sorted function so you might want to save the resulting list, as long as you're done changing the set. If you need to maintain unique elements and sorted, I agree with the suggestion of using OrderedDict from collections with an arbitrary value such as None.

blocks|key|1418983|text|如果您使用有序集来维护有序顺序，请考虑使用PyPI的有序集实现。sortedcontainers模块提供了一个用于此目的的SortedSet。一些好处:纯Python，快速的C实现，100%25的单元测试覆盖率，数小时的压力测试。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1418984|使用pip从PyPI安装很容易：|1418985|pip+install+sortedcontainers|code-block|syntax|javascript|1418986|请注意，如果无法pip+install，只需从open-source+repository中拉下sortedlist.py和sortedset.py文件即可。|style|CODE|1418987|安装后，您只需执行以下操作：|1418988|from+sortedcontainers+import+SortedSet
help(SortedSet)|1418989|sortedcontainers模块还维护了一个带有几个可选实现的performance+comparison。|1418990|对于询问Python的bag数据类型的注释，也可以使用SortedList数据类型，该数据类型可用于高效地实现bag。|1418991|entityMap|0|LINK|mutability|MUTABLE|url|http://www.grantjenks.com/docs/sortedcontainers/|1|http://www.grantjenks.com/docs/sortedcontainers/sortedset.html|2|https://github.com/grantjenks/sorted_containers|3|http://www.grantjenks.com/docs/sortedcontainers/performance.html|4|http://www.grantjenks.com/docs/sortedcontainers/sortedlist.html^0|W|G|0|1P|9|1|0|0|0|8|B|N|M|2|0|0|0|X|M|3|0|R|A|4|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@$A|1D|B|1E|1|1F]|$A|1G|B|1H|1|1I]]|C|$]]|$1|D|3|E|5|6|7|1J|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|1K|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|1L|8|@$A|1M|B|1N|M|N]]|9|@$A|1O|B|1P|1|1Q]]|C|$]]|$1|O|3|P|5|6|7|1R|8|@]|9|@]|C|$]]|$1|Q|3|R|5|H|7|1S|8|@]|9|@]|C|$I|J]]|$1|S|3|T|5|6|7|1T|8|@]|9|@$A|1U|B|1V|1|1W]]|C|$]]|$1|U|3|V|5|6|7|1X|8|@]|9|@$A|1Y|B|1Z|1|20]]|C|$]]|$1|W|3|-4|5|6|7|21|8|@]|9|@]|C|$]]]|X|$Y|$5|Z|10|11|C|$12|13]]|14|$5|Z|10|11|C|$12|15]]|16|$5|Z|10|11|C|$12|17]]|18|$5|Z|10|11|C|$12|19]]|1A|$5|Z|10|11|C|$12|1B]]]]

If you're using the ordered set to maintain a sorted order, consider using a sorted set implementation from PyPI. The <a href="http://www.grantjenks.com/docs/sortedcontainers/">sortedcontainers</a> module provides a <a href="http://www.grantjenks.com/docs/sortedcontainers/sortedset.html">SortedSet</a> for just this purpose. Some benefits: pure-Python, fast-as-C implementations, 100% unit test coverage, hours of stress testing.

Installing from PyPI is easy with pip:

<pre><code>pip install sortedcontainers
</code></pre>

Note that if you can't <code>pip install</code>, simply pull down the sortedlist.py and sortedset.py files from the <a href="https://github.com/grantjenks/sorted_containers">open-source repository</a>.

Once installed you can simply:

<pre><code>from sortedcontainers import SortedSet
help(SortedSet)
</code></pre>

The sortedcontainers module also maintains a <a href="http://www.grantjenks.com/docs/sortedcontainers/performance.html">performance comparison</a> with several alternative implementations.

For the comment that asked about Python's bag data type, there's alternatively a <a href="http://www.grantjenks.com/docs/sortedcontainers/sortedlist.html">SortedList</a> data type which can be used to efficiently implement a bag.

blocks|key|1203880|text|虽然有点晚，但我已经编写了一个setlist类作为collections-extended的一部分，它完全实现了Sequence和Set|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1203881|>>>+from+collections_extended+import+setlist
>>>+sl+=+setlist('abracadabra')
>>>+sl
setlist(('a',+'b',+'r',+'c',+'d'))
>>>+sl[3]
'c'
>>>+sl[-1]
'd'
>>>+'r'+in+sl++#+testing+for+inclusion+is+fast
True
>>>+sl.index('d')++#+so+is+finding+the+index+of+an+element
4
>>>+sl.insert(1,+'d')++#+inserting+an+element+already+in+raises+a+ValueError
ValueError
>>>+sl.index('d')
4|code-block|syntax|javascript|1203882|GitHub：https://github.com/mlenzen/collections-extended|1203883|文档：http://collections-extended.lenzm.net/en/latest/|1203884|PyPI：https://pypi.python.org/pypi/collections-extended|1203885|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/mlenzen/collections-extended|1|http://collections-extended.lenzm.net/en/latest/|2|https://pypi.python.org/pypi/collections-extended^0|F|7|P|K|1K|8|1T|3|0|0|7|1B|0|0|3|1C|1|0|5|1D|2|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1C|8|@]|D|@$9|1D|A|1E|1|1F]]|E|$]]|$1|M|3|N|5|6|7|1G|8|@]|D|@$9|1H|A|1I|1|1J]]|E|$]]|$1|O|3|P|5|6|7|1K|8|@]|D|@$9|1L|A|1M|1|1N]]|E|$]]|$1|Q|3|-4|5|6|7|1O|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]|10|$5|T|U|V|E|$W|11]]]]

A little late to the game, but I've written a class <code>setlist</code> as part of <code>collections-extended</code> that fully implements both <code>Sequence</code> and <code>Set</code>

<pre><code>&gt;&gt;&gt; from collections_extended import setlist
&gt;&gt;&gt; sl = setlist('abracadabra')
&gt;&gt;&gt; sl
setlist(('a', 'b', 'r', 'c', 'd'))
&gt;&gt;&gt; sl[3]
'c'
&gt;&gt;&gt; sl[-1]
'd'
&gt;&gt;&gt; 'r' in sl # testing for inclusion is fast
True
&gt;&gt;&gt; sl.index('d') # so is finding the index of an element
4
&gt;&gt;&gt; sl.insert(1, 'd') # inserting an element already in raises a ValueError
ValueError
&gt;&gt;&gt; sl.index('d')
4
</code></pre>

GitHub: <a href="https://github.com/mlenzen/collections-extended" rel="noreferrer">https://github.com/mlenzen/collections-extended</a>

Documentation: <a href="http://collections-extended.lenzm.net/en/latest/" rel="noreferrer">http://collections-extended.lenzm.net/en/latest/</a>

PyPI: <a href="https://pypi.python.org/pypi/collections-extended" rel="noreferrer">https://pypi.python.org/pypi/collections-extended</a>

blocks|key|1419086|text|如果您已经在代码中使用了pandas，那么它的Index对象的行为非常类似于有序集，如this+article中所示。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1419087|文章中的示例：|1419088|indA+=+pd.Index([1,+3,+5,+7,+9])
indB+=+pd.Index([2,+3,+5,+7,+11])

indA+&+indB++#+intersection
indA+%7C+indB++#+union
indA+-+indB++#+difference
indA+%5E+indB++#+symmetric+difference|code-block|syntax|javascript|1419089|entityMap|0|LINK|mutability|MUTABLE|url|https://www.oreilly.com/learning/introducing-pandas-objects^0|N|5|17|C|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

In case you're already using pandas in your code, its <code>Index</code> object behaves pretty like an ordered set, as shown in <a href="https://www.oreilly.com/learning/introducing-pandas-objects" rel="nofollow noreferrer">this article</a>.

Examples from the article:

<pre><code>indA = pd.Index([1, 3, 5, 7, 9])
indB = pd.Index([2, 3, 5, 7, 11])

indA &amp; indB # intersection
indA | indB # union
indA - indB # difference
indA ^ indB # symmetric difference
</code></pre>

blocks|key|1419138|text|我可以做一个比OrderedSet更好的例子:+boltons有一个a+pure-Python,+2/3-compatible+IndexedSet+type，它不仅是一个有序的集合，而且还支持索引(与列表一样)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1419139|只需pip+install+boltons+(或将setutils.py复制到代码库中)，导入IndexedSet并：|1419140|>>>+from+boltons.setutils+import+IndexedSet
>>>+x+=+IndexedSet(list(range(4))+%2B+list(range(8)))
>>>+x
IndexedSet([0,+1,+2,+3,+4,+5,+6,+7])
>>>+x+-+set(range(2))
IndexedSet([2,+3,+4,+5,+6,+7])
>>>+x[-1]
7
>>>+fcr+=+IndexedSet('freecreditreport.com')
>>>+''.join(fcr[:fcr.index('.')])
'frecditpo'|code-block|syntax|javascript|1419141|每件事都是独一无二的，而且都是有序的。完全公开:我写了IndexedSet，但这也意味着you+can+bug+me+if+there+are+any+issues。:)|1419142|entityMap|0|LINK|mutability|MUTABLE|url|http://boltons.readthedocs.org/en/latest/setutils.html|1|https://github.com/mahmoud/boltons/issues^0|1S|A|Y|19|0|0|2|J|P|B|1B|A|0|0|R|A|18|12|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|1B|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@$9|1F|A|1G|1|1H]]|E|$]]|$1|O|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

I can do you one better than an OrderedSet: boltons has <a href="http://boltons.readthedocs.org/en/latest/setutils.html" rel="noreferrer">a pure-Python, 2/3-compatible <code>IndexedSet</code> type</a> that is not only an ordered set, but also supports indexing (as with lists).

Simply <code>pip install boltons</code> (or copy <code>setutils.py</code> into your codebase), import the <code>IndexedSet</code> and:



<pre><code>&gt;&gt;&gt; from boltons.setutils import IndexedSet
&gt;&gt;&gt; x = IndexedSet(list(range(4)) + list(range(8)))
&gt;&gt;&gt; x
IndexedSet([0, 1, 2, 3, 4, 5, 6, 7])
&gt;&gt;&gt; x - set(range(2))
IndexedSet([2, 3, 4, 5, 6, 7])
&gt;&gt;&gt; x[-1]
7
&gt;&gt;&gt; fcr = IndexedSet('freecreditreport.com')
&gt;&gt;&gt; ''.join(fcr[:fcr.index('.')])
'frecditpo'
</code></pre>

Everything is unique and retained in order. Full disclosure: I wrote the <code>IndexedSet</code>, but that also means <a href="https://github.com/mahmoud/boltons/issues" rel="noreferrer">you can bug me if there are any issues</a>. :)

blocks|key|1204091|text|ParallelRegression包提供了一个setList(+)+ordered+set类，它的方法比基于ActiveState配方的选项更完整。它支持所有可用于列表的方法，以及大多数可用于集合的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1204092|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/rcbellamy/ParallelRegression|1|https://parallel-regression.readthedocs.io/en/latest/ParallelRegression.html#setlist^0|0|I|0|O|A|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

The <a href="https://github.com/rcbellamy/ParallelRegression" rel="nofollow noreferrer">ParallelRegression</a> package provides a <a href="https://parallel-regression.readthedocs.io/en/latest/ParallelRegression.html#setlist" rel="nofollow noreferrer">setList( )</a> ordered set class that is more method-complete than the options based on the ActiveState recipe. It supports all methods available for lists and most if not all methods available for sets.

blocks|key|1419298|text|官方库中没有OrderedSet。我对所有的数据结构做了一个详尽的小抄供你参考。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1419299|DataStructure+=+{
++++'Collections':+{
++++++++'Map':+[
++++++++++++('dict',+'OrderDict',+'defaultdict'),
++++++++++++('chainmap',+'types.MappingProxyType')
++++++++],
++++++++'Set':+[('set',+'frozenset'),+{'multiset':+'collection.Counter'}]
++++},
++++'Sequence':+{
++++++++'Basic':+['list',+'tuple',+'iterator']
++++},
++++'Algorithm':+{
++++++++'Priority':+['heapq',+'queue.PriorityQueue'],
++++++++'Queue':+['queue.Queue',+'multiprocessing.Queue'],
++++++++'Stack':+['collection.deque',+'queue.LifeQueue']
++++++++},
++++'text_sequence':+['str',+'byte',+'bytearray']
}|code-block|syntax|javascript|1419300|entityMap^0|6|A|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

There's no <code>OrderedSet</code> in official library.
I make an exhaustive cheatsheet of all the data structure for your reference.

<pre><code>DataStructure = {
 'Collections': {
 'Map': [
 ('dict', 'OrderDict', 'defaultdict'),
 ('chainmap', 'types.MappingProxyType')
 ],
 'Set': [('set', 'frozenset'), {'multiset': 'collection.Counter'}]
 },
 'Sequence': {
 'Basic': ['list', 'tuple', 'iterator']
 },
 'Algorithm': {
 'Priority': ['heapq', 'queue.PriorityQueue'],
 'Queue': ['queue.Queue', 'multiprocessing.Queue'],
 'Stack': ['collection.deque', 'queue.LifeQueue']
 },
 'text_sequence': ['str', 'byte', 'bytearray']
}
</code></pre>

blocks|key|1204273|text|因此，我也有一个很小的列表，其中我显然有可能引入非唯一值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1204274|我搜索了某种类型的唯一列表的存在，但后来意识到在添加元素之前测试它的存在效果很好。|1204275|if(not+new_element+in+my_list):
++++my_list.append(new_element)|code-block|syntax|javascript|1204276|我不知道这种简单的方法是否有需要注意的地方，但它解决了我的问题。|1204277|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

So i also had a small list where i clearly had the possibility of introducing non-unique values.

I searched for the existence of a unique list of some sort, but then realized that testing the existence of the element before adding it works just fine.

<pre><code>if(not new_element in my_list):
 my_list.append(new_element)
</code></pre>

I don't know if there are caveats to this simple approach, but it solves my problem.

blocks|key|1204376|text|正如其他答案所提到的，对于python+3.7%2B，字典是按定义排序的。我们可以使用字典的键来存储我们的值，而不是对OrderedDict进行子类化，对abc.collections.MutableSet或typing.MutableSet进行子类化。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1204377|import+itertools
import+typing

T+=+typing.TypeVar("T")

class+OrderedSet(typing.MutableSet[T]):
++++"""A+set+that+preserves+insertion+order+by+internally+using+a+dict."""

++++def+__init__(self,+iterable:+typing.Iterator[T]):
++++++++self._d+=+dict.fromkeys(iterable)

++++def+add(self,+x:+T)+->+None:
++++++++self._d[x]+=+None

++++def+discard(self,+x:+T)+->+None:
++++++++self._d.pop(x,+None)

++++def+__contains__(self,+x:+object)+->+bool:
++++++++return+self._d.__contains__(x)

++++def+__len__(self)+->+int:
++++++++return+self._d.__len__()

++++def+__iter__(self)+->+typing.Iterator[T]:
++++++++return+self._d.__iter__()

++++def+__str__(self):
++++++++return+f"{{{',+'.join(str(i)+for+i+in+self)}}}"

++++def+__repr__(self):
++++++++return+f"<OrderedSet+{self}>"|code-block|syntax|javascript|1204378|然后只需：|1204379|x+=+OrderedSet([1,+2,+-1,+"bar"])
x.add(0)
assert+list(x)+==+[1,+2,+-1,+"bar",+0]|1204380|I+added+this+code,+with+some+tests,+in+a+small+library，所以任何人都可以直接pip+install它。|1204381|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/bustawin/ordered-set-37^0|1L|B|23|Q|2U|H|0|0|0|0|1T|B|0|1I|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|Q|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

As other answers mention, as for python 3.7+, the dict is ordered by definition. Instead of subclassing <code>OrderedDict</code> we can subclass <code>abc.collections.MutableSet</code> or <code>typing.MutableSet</code> using the dict's keys to store our values.
<pre class="lang-py prettyprint-override"><code>import itertools
import typing

T = typing.TypeVar(&quot;T&quot;)

class OrderedSet(typing.MutableSet[T]):
 &quot;&quot;&quot;A set that preserves insertion order by internally using a dict.&quot;&quot;&quot;

 def __init__(self, iterable: typing.Iterator[T]):
 self._d = dict.fromkeys(iterable)

 def add(self, x: T) -&gt; None:
 self._d[x] = None

 def discard(self, x: T) -&gt; None:
 self._d.pop(x, None)

 def __contains__(self, x: object) -&gt; bool:
 return self._d.__contains__(x)

 def __len__(self) -&gt; int:
 return self._d.__len__()

 def __iter__(self) -&gt; typing.Iterator[T]:
 return self._d.__iter__()

 def __str__(self):
 return f&quot;{{{', '.join(str(i) for i in self)}}}&quot;

 def __repr__(self):
 return f&quot;&lt;OrderedSet {self}&gt;&quot;
</code></pre>
Then just:
<pre class="lang-py prettyprint-override"><code>x = OrderedSet([1, 2, -1, &quot;bar&quot;])
x.add(0)
assert list(x) == [1, 2, -1, &quot;bar&quot;, 0]
</code></pre>
<a href="https://github.com/bustawin/ordered-set-37" rel="nofollow noreferrer">I added this code, with some tests, in a small library</a>, so anyone can just <code>pip install</code> it.

Python has an <a href="http://www.python.org/dev/peps/pep-0372/" rel="noreferrer">ordered dictionary</a>. What about an ordered set?

问Python有有序集吗？
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