Re: [a,b,c,d] = 1,2,3,4
On 8/26/2015 8:21 AM, Tim Chase wrote: a, b, c = (x for x in range(3)) # a generator for instance Since range() *is* a generator, why not just use In Python 3, range is a sequence class with a separate iterator class >>> r = range(3) >>> r range(0, 3) >>> iter(r) Like all sequences, a range object can be iterated multiple times as a new iterator is used each time. >>> list(r) [0, 1, 2] >>> list(r) [0, 1, 2] -- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
- Original Message - > From: "Chris Angelico" > Cc: python-list@python.org > Sent: Wednesday, 26 August, 2015 3:04:05 PM > Subject: Re: [a,b,c,d] = 1,2,3,4 > > On Wed, Aug 26, 2015 at 12:59 AM, Jean-Michel Pichavant > wrote: > > To add to Joel's answer, the right side can be *any* sequence, and > > is not restricted to lists or tuples. > > > > a, b, c = (x for x in range(3)) # a generator for instance > > FWIW, a generator is not a sequence; this works because the right > side > can be any *iterable*, even more general than sequences. > > ChrisA Sorry about that, I've been mislead by the tutorial which uses sequence where it should have used iterable, so I though they where the same but they're not. https://docs.python.org/2/library/stdtypes.html "There are seven sequence types: strings, Unicode strings, lists, tuples, bytearrays, buffers, and xrange objects." I stand corrected. JM -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On Wed, Aug 26, 2015 at 12:59 AM, Jean-Michel Pichavant wrote: > To add to Joel's answer, the right side can be *any* sequence, and is not > restricted to lists or tuples. > > a, b, c = (x for x in range(3)) # a generator for instance FWIW, a generator is not a sequence; this works because the right side can be any *iterable*, even more general than sequences. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On 2015-08-25 16:59, Jean-Michel Pichavant wrote: > - Original Message - > > From: "Joel Goldstick" > > its called list unpacking or packing (?) > > > > the right side is considered a tuple because of the commas > > >>> a = 1,2,3 > > >>> a > > (1, 2, 3) > > >>> a[1] > > 2 > > To add to Joel's answer, the right side can be *any* sequence, and > is not restricted to lists or tuples. > > a, b, c = (x for x in range(3)) # a generator for instance Since range() *is* a generator, why not just use a, b, c = range(3) I do this often for setting constants: ( HR_FILE, PHONE_FILE, COST_CENTERS_FILE, ) = range(3) however I have to keep track of how many entries are in there. When Py3 introduced variable tuple unpacking, I'd hoped the last one wouldn't consume generators, allowing me to do something like ( HR_FILE, PHONE_FILE, COST_CENTERS, *_ ) = itertools.count() so I could insert additional constants and have the list automatically adjust. Alas, no such joy. The new Enum class does offer an auto-number functionality, but it's clunky, IMHO. https://docs.python.org/3/library/enum.html#autonumber -tkc -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
- Original Message - > From: "Joel Goldstick" > its called list unpacking or packing (?) > > the right side is considered a tuple because of the commas > >>> a = 1,2,3 > >>> a > (1, 2, 3) > >>> a[1] > 2 To add to Joel's answer, the right side can be *any* sequence, and is not restricted to lists or tuples. a, b, c = (x for x in range(3)) # a generator for instance That would be a generator unpacking combined with a tuple packing (is packing restricted to tuples and lists ? probably) JM -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
Ian Kelly writes:
> On Tue, Aug 25, 2015 at 9:32 AM, Skip Montanaro wrote:
>> On Tue, Aug 25, 2015 at 10:24 AM, Jussi Piitulainen wrote:
>>>
>>> When I try it today, round brackets also work, both in 2.6.6 and
>>> 3.4.0 - no idea what version it was where they failed or if I'm
>>> imagining the whole thing.
>>
>> You are imagining the whole thing. Either that, or you had some other
>> problem with your tuple unpacking which kept it from working. That
>> has been a part of the language as far back as I can remember. I
>> started using Python around the 1.0 timeframe.
>
> My guess is that Jussi was trying to unpack a sequence of a single
> element like this:
>
> (a) = some_sequence
[snip]
It wasn't that. It was a known number of tab-separated fields that I
wanted to name individually, like this:
ID, FORM, LEMMA, POS, MOR, FEATS, \
HEAD, REL, DEPS, MISC \
= line.split('\t')
That's from actual code but not necessarily from the place where I first
tried and failed to use parentheses. It didn't occur to me to try square
brackets, so I got in the habit of using backslashes as above. (That
script is dated in January 2015. The something that happened happened
some months before that. But it may have been a hallucination.)
--
https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
Skip Montanaro writes: > On Tue, Aug 25, 2015 at 10:24 AM, Jussi Piitulainen wrote: > >> When I try it today, round brackets also work, both in 2.6.6 and >> 3.4.0 - no idea what version it was where they failed or if I'm >> imagining the whole thing. > > You are imagining the whole thing. Either that, or you had some other > problem with your tuple unpacking which kept it from working. That has > been a part of the language as far back as I can remember. I started > using Python around the 1.0 timeframe. At least they work now, and clearly are intended to work. But I just checked and I have scripts with backslash-terminated lines where I'm sure I wanted to use those brackets. Could it have been some sort of temporary regression? Well, never mind :) -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On Tue, Aug 25, 2015 at 9:32 AM, Skip Montanaro wrote: > > On Tue, Aug 25, 2015 at 10:24 AM, Jussi Piitulainen > wrote: >> >> When I try it today, round brackets >> also work, both in 2.6.6 and 3.4.0 - no idea what version it was where >> they failed or if I'm imagining the whole thing. > > > You are imagining the whole thing. Either that, or you had some other > problem with your tuple unpacking which kept it from working. That has been > a part of the language as far back as I can remember. I started using Python > around the 1.0 timeframe. My guess is that Jussi was trying to unpack a sequence of a single element like this: (a) = some_sequence With the result that a is assigned the whole sequence instead of the one element, because (a) does not denote a tuple, but merely an individual parenthesized expression. Any of these would work in its place: (a,) = some_sequence a, = some_sequence [a] = some_sequence -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On Tue, Aug 25, 2015 at 10:24 AM, Jussi Piitulainen < harvested.address@is.invalid> wrote: > When I try it today, round brackets > also work, both in 2.6.6 and 3.4.0 - no idea what version it was where > they failed or if I'm imagining the whole thing. > You are imagining the whole thing. Either that, or you had some other problem with your tuple unpacking which kept it from working. That has been a part of the language as far back as I can remember. I started using Python around the 1.0 timeframe. Skip -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
"ast" writes: >>>> [a,b,c,d] = 1,2,3,4 >>>> a > 1 >>>> b > 2 >>>> c > 3 >>>> d > 4 > > I have never seen this syntax before. Is it documented. > Is there a name for that ? I remember being unhappy when a similar assignment with round brackets turned out to be invalid syntax. Then I learned (in this newsgroup) that square brackets would work, and so they did, and then I was happy again, though it felt a bit inconsistent. When I try it today, round brackets also work, both in 2.6.6 and 3.4.0 - no idea what version it was where they failed or if I'm imagining the whole thing. The page that Joel Goldstick cited claims that Guido van Rossum himself has called the left side of a statement like "w,x,y,z = t3" (no brackets on that page) "the list of variables" (but their link to the evidence is dead). -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
"Joel Goldstick" a écrit dans le message de news:mailman.27.1440515128.11709.python-l...@python.org... On Tue, Aug 25, 2015 at 10:32 AM, Cody Piersall wrote: On Tue, Aug 25, 2015 at 9:16 AM, ast wrote: The original example is one I haven't seen in the wild. I found it using matplotlib import numpy as np import matplotlib.pyplot as plt f, (ax1, ax2) = plt.subplots(2, 1, sharex=True) -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
"ast" a écrit dans le message de news:55dc853c$0$3083$426a7...@news.free.fr... "Joel Goldstick" a écrit dans le message de news:mailman.23.1440513059.11709.python-l...@python.org... On Tue, Aug 25, 2015 at 10:16 AM, ast wrote: [a,b,c,d] = 1,2,3,4 a 1 b 2 c 3 d 4 I have never seen this syntax before. Is it documented. Is there a name for that ? thx -- https://mail.python.org/mailman/listinfo/python-list its called list unpacking or packing (?) the right side is considered a tuple because of the commas a = 1,2,3 a (1, 2, 3) a[1] 2 http://www.developer.com/lang/other/article.php/630101/Learn-to-Program-using-Python-Unpacking-Tuples.htm -- Joel Goldstick http://joelgoldstick.com Yes you are right, it is related to tuple unpacking Here are some useful examples I found. http://svn.python.org/projects/python/branches/pep-0384/Lib/test/test_unpack_ex.py Unpack in list >>> [a, *b, c] = range(5) >>> a == 0 and b == [1, 2, 3] and c == 4 True -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
"Joel Goldstick" a écrit dans le message de news:mailman.23.1440513059.11709.python-l...@python.org... On Tue, Aug 25, 2015 at 10:16 AM, ast wrote: [a,b,c,d] = 1,2,3,4 a 1 b 2 c 3 d 4 I have never seen this syntax before. Is it documented. Is there a name for that ? thx -- https://mail.python.org/mailman/listinfo/python-list its called list unpacking or packing (?) the right side is considered a tuple because of the commas a = 1,2,3 a (1, 2, 3) a[1] 2 http://www.developer.com/lang/other/article.php/630101/Learn-to-Program-using-Python-Unpacking-Tuples.htm -- Joel Goldstick http://joelgoldstick.com Yes you are right, it is related to tuple unpacking Here are some useful examples I found. http://svn.python.org/projects/python/branches/pep-0384/Lib/test/test_unpack_ex.py -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On Tue, Aug 25, 2015 at 10:32 AM, Cody Piersall wrote: > > > On Tue, Aug 25, 2015 at 9:16 AM, ast wrote: >>>>> >>>>> [a,b,c,d] = 1,2,3,4 >>>>> a >> >> 1 >>>>> >>>>> b >> >> 2 >>>>> >>>>> c >> >> 3 >>>>> >>>>> d >> >> 4 >> >> I have never seen this syntax before. Is it documented. >> Is there a name for that ? >> >> thx >> -- >> https://mail.python.org/mailman/listinfo/python-list > > > That's called "sequence unpacking" > > Cody > > -- > https://mail.python.org/mailman/listinfo/python-list > The original example is one I haven't seen in the wild. One nifty use of this feature is to exchange values like this: a, b = b, a it saves the use of a temporary name -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
- Original Message - > From: "ast" > To: python-list@python.org > Sent: Tuesday, 25 August, 2015 4:16:17 PM > Subject: [a,b,c,d] = 1,2,3,4 > > >>> [a,b,c,d] = 1,2,3,4 > >>> a > 1 > >>> b > 2 > >>> c > 3 > >>> d > 4 > > I have never seen this syntax before. Is it documented. > Is there a name for that ? > > thx You probably have already seen something like: a,b,c,d = 1,2,3,4 which is the same code than yours with the list replaced by a tuple. Moreover: https://docs.python.org/2/tutorial/datastructures.html """ x, y, z = t This is called, appropriately enough, sequence unpacking and works for any sequence on the right-hand side. Sequence unpacking requires the list of variables on the left to have the same number of elements as the length of the sequence. Note that multiple assignment is really just a combination of tuple packing and sequence unpacking. """ It's slightly confusing because it mentions a "list of variable" and then a "tuple packing" while the example uses a tuple. Fortunately, lists and tuples can be used in both cases. JM -- IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you. -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On Tue, Aug 25, 2015 at 9:16 AM, ast wrote: > [a,b,c,d] = 1,2,3,4 >>>> a >>>> >>> 1 > >> b >>>> >>> 2 > >> c >>>> >>> 3 > >> d >>>> >>> 4 > > I have never seen this syntax before. Is it documented. > Is there a name for that ? > > thx > -- > https://mail.python.org/mailman/listinfo/python-list > That's called "sequence unpacking" Cody -- https://mail.python.org/mailman/listinfo/python-list
Re: [a,b,c,d] = 1,2,3,4
On Tue, Aug 25, 2015 at 10:16 AM, ast wrote: >>>> [a,b,c,d] = 1,2,3,4 >>>> a > > 1 >>>> >>>> b > > 2 >>>> >>>> c > > 3 >>>> >>>> d > > 4 > > I have never seen this syntax before. Is it documented. > Is there a name for that ? > > thx > -- > https://mail.python.org/mailman/listinfo/python-list its called list unpacking or packing (?) the right side is considered a tuple because of the commas >>> a = 1,2,3 >>> a (1, 2, 3) >>> a[1] 2 >>> http://www.developer.com/lang/other/article.php/630101/Learn-to-Program-using-Python-Unpacking-Tuples.htm -- Joel Goldstick http://joelgoldstick.com -- https://mail.python.org/mailman/listinfo/python-list
[a,b,c,d] = 1,2,3,4
[a,b,c,d] = 1,2,3,4 a 1 b 2 c 3 d 4 I have never seen this syntax before. Is it documented. Is there a name for that ? thx -- https://mail.python.org/mailman/listinfo/python-list
