blocks|key|843276|text|这样如何：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|843277|from+operator+import+itemgetter
itemgetter(0,2,3)(myList)
('foo',+'baz',+'quux')|code-block|syntax|javascript|843278|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

What about this:

<pre><code>from operator import itemgetter
itemgetter(0,2,3)(myList)
('foo', 'baz', 'quux')
</code></pre>

blocks|key|843341|text|它不是内置的，但是如果你愿意，你可以创建一个接受元组作为“索引”的list的子类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|843342|class+MyList(list):

++++def+__getitem__(self,+index):
++++++++if+isinstance(index,+tuple):
++++++++++++return+[self[i]+for+i+in+index]
++++++++return+super(MyList,+self).__getitem__(index)


seq+=+MyList("foo+bar+baaz+quux+mumble".split())
print+seq[0]
print+seq[2,4]
print+seq[1::2]|code-block|syntax|javascript|843343|打印|843344|foo
['baaz',+'mumble']
['bar',+'quux']|843345|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

It isn't built-in, but you can make a subclass of list that takes tuples as "indexes" if you'd like:

<pre><code>class MyList(list):

 def __getitem__(self, index):
 if isinstance(index, tuple):
 return [self[i] for i in index]
 return super(MyList, self).__getitem__(index)


seq = MyList("foo bar baaz quux mumble".split())
print seq[0]
print seq[2,4]
print seq[1::2]
</code></pre>

printing

<pre><code>foo
['baaz', 'mumble']
['bar', 'quux']
</code></pre>

blocks|key|843400|text|也许列表理解是按顺序进行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|843401|L+=+['a',+'b',+'c',+'d',+'e',+'f']
print+[+L[index]+for+index+in+[1,3,5]+]|code-block|syntax|javascript|843402|产生：|843403|['b',+'d',+'f']|843404|这就是你要找的吗？|843405|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Maybe a list comprehension is in order:

<pre><code>L = ['a', 'b', 'c', 'd', 'e', 'f']
print [ L[index] for index in [1,3,5] ]
</code></pre>

Produces:

<pre><code>['b', 'd', 'f']
</code></pre>

Is that what you are looking for?

blocks|key|627784|text|>>>+map(myList.__getitem__,+(2,2,1,3))
('baz',+'baz',+'bar',+'quux')|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|627785|如果您想要执行myList[(2,2,1,3)]，还可以创建自己的List类，该类支持将元组作为__getitem__的参数。|unstyled|offset|length|style|CODE|627786|entityMap^0|0|7|H|X|4|1C|B|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]|$G|Q|H|R|I|J]|$G|S|H|T|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|U|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>&gt;&gt;&gt; map(myList.__getitem__, (2,2,1,3))
('baz', 'baz', 'bar', 'quux')
</code></pre>

You can also create your own <code>List</code> class which supports tuples as arguments to <code>__getitem__</code> if you want to be able to do <code>myList[(2,2,1,3)]</code>.

blocks|key|627817|text|我只想指出，即使是itemgetter的语法看起来也很整洁，但在大型列表上执行时有点慢。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|627818|import+timeit
from+operator+import+itemgetter
start=timeit.default_timer()
for+i+in+range(1000000):
++++itemgetter(0,2,3)(myList)
print+("Itemgetter+took+",+(timeit.default_timer()-start))|code-block|syntax|javascript|627819|Itemgetter拿到了1.065209062149279|627820|start=timeit.default_timer()
for+i+in+range(1000000):
++++myList[0],myList[2],myList[3]
print+("Multiple+slice+took+",+(timeit.default_timer()-start))|627821|多个切片占0.6225321444745759|627822|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I just want to point out, even syntax of itemgetter looks really neat, but it's kinda slow when perform on large list.

<pre><code>import timeit
from operator import itemgetter
start=timeit.default_timer()
for i in range(1000000):
 itemgetter(0,2,3)(myList)
print ("Itemgetter took ", (timeit.default_timer()-start))
</code></pre>

Itemgetter took 1.065209062149279

<pre><code>start=timeit.default_timer()
for i in range(1000000):
 myList[0],myList[2],myList[3]
print ("Multiple slice took ", (timeit.default_timer()-start))
</code></pre>

Multiple slice took 0.6225321444745759

blocks|key|843567|text|另一种可能的解决方案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|843568|sek=[]
L=[1,2,3,4,5,6,7,8,9,0]
for+i+in+[2,+4,+7,+0,+3]:
+++a=[L[i]]
+++sek=sek%2Ba
print+(sek)|code-block|syntax|javascript|843569|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Another possible solution:

<pre><code>sek=[]
L=[1,2,3,4,5,6,7,8,9,0]
for i in [2, 4, 7, 0, 3]:
 a=[L[i]]
 sek=sek+a
print (sek)
</code></pre>

blocks|key|843625|text|就像通常有一个像mask这样的布尔型数值数组一样|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|843626|[mylist[i]+for+i+in+np.arange(len(mask),+dtype=int)[mask]]|843627|一个适用于任何序列或np.array的lambda：|843628|subseq+=+lambda+myseq,+mask+:+[myseq[i]+for+i+in+np.arange(len(mask),+dtype=int)[mask]]|843629|newseq+=+subseq(myseq,+mask)|843630|entityMap^0|8|4|0|0|1M|0|0|0|2F|0|0|S|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|V|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|O|$]]

like often when you have a boolean numpy array like <code>mask</code>

<code>[mylist[i] for i in np.arange(len(mask), dtype=int)[mask]]</code>

A lambda that works for any sequence or np.array:

<code>subseq = lambda myseq, mask : [myseq[i] for i in np.arange(len(mask), dtype=int)[mask]]</code>

<code>newseq = subseq(myseq, mask)</code>

I have the following Python list (can also be a tuple):

<pre><code>myList = ['foo', 'bar', 'baz', 'quux']
</code></pre>

I can say

<pre><code>&gt;&gt;&gt; myList[0:3]
['foo', 'bar', 'baz']
&gt;&gt;&gt; myList[::2]
['foo', 'baz']
&gt;&gt;&gt; myList[1::2]
['bar', 'quux']
</code></pre>

How do I explicitly pick out items whose indices have no specific patterns? For example, I want to select <code>[0,2,3]</code>. Or from a very big list of 1000 items, I want to select <code>[87, 342, 217, 998, 500]</code>. Is there some Python syntax that does that? Something that looks like:

<pre><code>&gt;&gt;&gt; myBigList[87, 342, 217, 998, 500]
</code></pre>

Explicitly select items from a list or tuple

Python

我有以下Python列表(也可以是元组)：myList = ['foo', 'bar', 'baz', 'quux']我可以说>>> myList[0:3]['foo', 'bar', 'baz']>>> myList[::2]['foo', 'baz']>>> myList[1::2]['bar', 'quux']如...

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