blocks|key|86494|text|您可以使用生成器表达式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|86495|tuple(i+for+i+in+(1,+2,+3))|code-block|syntax|javascript|86496|但是…的括号已经用过了。生成器表达式。|86497|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|$]]

You can use a generator expression:

<pre><code>tuple(i for i in (1, 2, 3))
</code></pre>

but parentheses were already taken for … generator expressions.

blocks|key|86683|text|Since+Python+3.5，您还可以使用splat+*解包语法来解包生成器表达式：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|86684|*(x+for+x+in+range(10)),|code-block|syntax|javascript|86685|entityMap|0|LINK|mutability|MUTABLE|url|https://www.python.org/dev/peps/pep-0448/^0|T|1|0|G|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

<a href="https://www.python.org/dev/peps/pep-0448/" rel="noreferrer">Since Python 3.5</a>, you can also use splat <code>*</code> unpacking syntax to unpack a generator expresion:

<pre><code>*(x for x in range(10)),
</code></pre>

blocks|key|86520|text|理解是通过循环或迭代项目并将其分配到容器中来工作的，元组无法接收分配。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|86521|一旦创建了元组，就不能对其进行追加、扩展或赋值。修改元组的唯一方法是如果它的一个对象本身可以被分配给(是一个非元组容器)。因为Tuple只持有对这类对象的引用。|86522|另外-一个元组有它自己的构造器tuple()，你可以给它任何迭代器。这意味着要创建一个元组，您可以这样做：|offset|length|style|CODE|86523|tuple(i+for+i+in+(1,2,3))|code-block|syntax|javascript|86524|entityMap^0|0|0|F|7|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|S|8|@$F|T|G|U|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|V|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Comprehension works by looping or iterating over items and assigning them into a container, a Tuple is unable to receive assignments.

Once a Tuple is created, it can not be appended to, extended, or assigned to. The only way to modify a Tuple is if one of its objects can itself be assigned to (is a non-tuple container). Because the Tuple is only holding a reference to that kind of object.

Also - a tuple has its own constructor <code>tuple()</code> which you can give any iterator. Which means that to create a tuple, you could do:

<pre><code>tuple(i for i in (1,2,3))
</code></pre>

blocks|key|86474|text|我最好的猜测是他们用完了括号，认为添加一个“丑陋”的语法没有足够的用处……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|86475|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

My best guess is that they ran out of brackets and didn't think it would be useful enough to warrent adding an "ugly" syntax ...

blocks|key|86538|text|元组不能像列表一样有效地追加。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|86539|因此，元组理解需要在内部使用列表，然后转换为元组。|86540|这和你现在要做的是一样的:+tuple(理解)|86541|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Tuples cannot efficiently be appended like a list. 

So a tuple comprehension would need to use a list internally and then convert to a tuple. 

That would be the same as what you do now : tuple( [ comprehension ] )

blocks|key|303863|text|圆括号不会创建元组。也就是one+=+(two)不是元组。唯一的解决方法是one+=+(two，)或one+=+tuple(two)。因此，一个解决方案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|303864|tuple(i+for+i+in+myothertupleorlistordict)+|code-block|syntax|javascript|303865|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|$]]

Parentheses do not create a tuple. aka one = (two) is not a tuple. The only way around is either one = (two,) or one = tuple(two). So a solution is:

<pre><code>tuple(i for i in myothertupleorlistordict) 
</code></pre>

blocks|key|86716|text|在我的python+(3.5)中，使用带有来自collections的deque的生成器比使用list理解要快一点：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|86717|>>>+from+collections+import+deque
>>>+timeit.timeit(lambda:+tuple([i+for+i+in+range(10000000)]),number=10)
9.294099200000005
>>>+timeit.timeit(lambda:+tuple(deque((i+for+i+in+range(10000000)))),number=10)
9.007653800000014|code-block|syntax|javascript|86718|entityMap^0|N|B|Z|5|1B|4|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|$]]

On my python (3.5) using a generator with <code>deque</code> from <code>collections</code> is slightly quicker then using a <code>list</code> comprehension:
<pre><code>&gt;&gt;&gt; from collections import deque
&gt;&gt;&gt; timeit.timeit(lambda: tuple([i for i in range(10000000)]),number=10)
9.294099200000005
&gt;&gt;&gt; timeit.timeit(lambda: tuple(deque((i for i in range(10000000)))),number=10)
9.007653800000014
</code></pre>

blocks|key|86756|text|因为您不能将项追加到元组。这就是如何将简单的列表理解转换为更基本的python代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|86757|_list+=+[1,2,3,4,5]
clist+=+[+i*i+for+i+in+_list+]
print(clist)

clist1+=+[]
for+i+in+_list:
++++clist1.append(i*i)
print(clist1)|code-block|syntax|javascript|86758|现在，在上面的例子中使用元组理解意味着将项目附加到元组中，这是不允许的。不过，一旦这个列表准备就绪，您可以使用tuple(clist1)将其转换为一个元组|offset|length|style|CODE|86759|entityMap^0|0|0|1J|D|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]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Because you can not append items to a tuple. This is how a simple list comprehension can be converted into more basic python code.
<pre><code>_list = [1,2,3,4,5]
clist = [ i*i for i in _list ]
print(clist)

clist1 = []
for i in _list:
 clist1.append(i*i)
print(clist1)
</code></pre>
Now using a tuple comprehension for above example means appending items into a tuple which is not allowed. Though you can covert this list to a tuple once it is ready by using <code>tuple(clist1)</code>

blocks|key|303822|text|我们可以从列表理解中生成元组。下面的代码将两个数字按顺序添加到一个元组中，并给出一个从0到9的列表。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|303823|>>>+print+k
[0,+1,+2,+3,+4,+5,+6,+7,+8,+9,+10,+11,+12,+13,+14,+15,+16,+17,+18,+19,+20,+21,+22,+23,+24,+25,+26,+27,+28,+29,+30,+31,+32,+33,+34,+35,+36,+37,+38,+39,+40,+41,+42,+43,+44,+45,+46,+47,+48,+49,+50,+51,+52,+53,+54,+55,+56,+57,+58,+59,+60,+61,+62,+63,+64,+65,+66,+67,+68,+69,+70,+71,+72,+73,+74,+75,+76,+77,+78,+79,+80,+81,+82,+83,+84,+85,+86,+87,+88,+89,+90,+91,+92,+93,+94,+95,+96,+97,+98,+99]
>>>+r=+[tuple(k[i:i%2B2])+for+i+in+xrange(10)+if+not+i%252]
>>>+print+r
[(0,+1),+(2,+3),+(4,+5),+(6,+7),+(8,+9)]|code-block|syntax|javascript|303824|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|$]]

We can generate tuples from a list comprehension. The following one adds two numbers sequentially into a tuple and gives a list from numbers 0-9.

<pre><code>&gt;&gt;&gt; print k
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
&gt;&gt;&gt; r= [tuple(k[i:i+2]) for i in xrange(10) if not i%2]
&gt;&gt;&gt; print r
[(0, 1), (2, 3), (4, 5), (6, 7), (8, 9)]
</code></pre>

As we all know, there's list comprehension, like

<pre><code>[i for i in [1, 2, 3, 4]]
</code></pre>

and there is dictionary comprehension, like

<pre><code>{i:j for i, j in {1: 'a', 2: 'b'}.items()}
</code></pre>

but

<pre><code>(i for i in (1, 2, 3))
</code></pre>

will end up in a generator, not a <code>tuple</code> comprehension. Why is that?

My guess is that a <code>tuple</code> is immutable, but this does not seem to be the answer.

Why is there no tuple comprehension in Python?

容器

我们都知道，有列表理解，比如[i for i in [1, 2, 3, 4]]还有字典的理解，比如{i:j for i, j in {1: 'a', 2: 'b'}.items()}但(i for i in (1, 2, 3))将在生成器中结束，而不是tuple理解。为什么会这样呢？我的猜测是tuple是不可变的，但这似乎不是答案。

问为什么Python中没有元组理解？
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