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Groups > comp.lang.python > #96514
| From | Akira Li <4kir4.1i@gmail.com> |
|---|---|
| Subject | Re: Terminology: "reference" versus "pointer" |
| Date | 2015-09-13 21:04 +0300 |
| References | (16 earlier) <1a1a1f6a-27ce-4c1b-807a-43eabaa04abb@googlegroups.com> <mailman.435.1442080562.8327.python-list@python.org> <04ca9d7c-d02b-4329-bd94-4d18d86b3edf@googlegroups.com> <87egi375wb.fsf@gmail.com> <m21te3qqeg.fsf@fastmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.486.1442167558.8327.python-list@python.org> (permalink) |
Random832 <random832@fastmail.com> writes:
> Akira Li <4kir4.1i@gmail.com> writes:
>>Rustom Mody <rustompmody@gmail.com> writes:
>>> viz. I have two variables (or names!) say a and b which look the same
>>>>>> a
>>> [[1,2],[1,2]]
>>>>>> b
>>> [[1,2],[1,2]]
>>> And yet doing
>>>>>> a[0][0] = "Oops!"
>>> gives a data structure one "Oops!"
>>> whereas doing it to b mysteriously gives 2
>>
>> Sorry, I haven't followed the whole thread. Could your provide a
>> complete code example? Mention what you expect to happen and what
>> happens instead in your case.
>
> a0 = a1 = [1, 2]
> b0 = [1, 2]
> b1 = [1, 2]
> a = [a0, a1]
> b = [b0, b1]
> del a0, a1, b0, b1
>
> There's nothing about *him* expecting anything wrong to happen. The
> question is how to draw a diagram that unambiguously shows the resulting
> structure using the "parcel tags" model shown in the diagrams (and
> without having a0/a1/etc as actual names)
I'm not sure what "parcel tags" model is but if you mean these
pictures[1] than it works in this case as well as any other (take *a*,
*b* nametags, put them on the corresponding balloons that represents
list objects).
The only names left are *a* and *b* that refer to the corresponding
lists. There is no ambiguity there to put *a*, *b* nametags.
Lists as any other containers contain references to other objects and
therefore "box and arrows" model provides _more details_ here[2,3]
> If the "parcel tags" model can't show it, then the "parcel tag" model
> clearly is not a correct and complete depiction of how Python actually
> works.
> (If I were drawing a picture rather than ASCII I'd add something to make
> it clear that the pairs shown are list objects Like, it's a circle with
> the word "list" and two pointer-boxes inside it.)
"correct and complete" is impossible in the general case for any model.
Imagine what happens if numpy arrays are used instead of Python lists:
lst = [numpy.array([1, 2]) for _ in range(3)]
a = [lst[0], lst[0]]
b = [lst[1], lst[2]]
Note: there could be no a[0][0], a[0][1], etc corresponding Python
objects until you explicitly reference them in the code. If there are no
Python objects then you can't draw any arrows and therefore "box and
arrows" model is incomplete.
Or consider this collections of all Unicode characters:
class U:
def __len__(self):
return sys.maxunicode + 1
def __getitem__(self, index):
if index < 0:
index += len(self)
if 0 <= index < len(self):
return chr(index)
raise IndexError(index)
u = U()
print(u[0x61]) # -> a
In this example, it is even more clear that the corresponding items
might not exist until they are explicitly referenced in a program. *u*
is a sequence as any other in Python (it is easy to make it
*collections.abc.Sequence* compatible).
Or this:
lst = [range(1, 3) for _ in range(3)]
a = [lst[0], lst[0]]
b = [lst[1], lst[2]]
In Python 2, it is the exact replica of the original example. In Python
3, it is the same if you don't need to mutate the ranges. Again, the
leaf objects might not exist until you reference them in the code in
Python 3.
Finally, consider a Python sequence that uses os.urandom()
internally. No model will predict the result (and therefore no model is
complete) in this case.
[1]
http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#python-has-names
[2]
http://www.pythontutor.com/visualize.html#code=a0+%3D+a1+%3D+%5B1,+2%5D%0Ab0+%3D+%5B1,+2%5D%0Ab1+%3D+%5B1,+2%5D%0Aa+%3D+%5Ba0,+a1%5D%0Ab+%3D+%5Bb0,+b1%5D%0Adel+a0,+a1,+b0,+b1%0A&mode=display&origin=opt-frontend.js&cumulative=false&heapPrimitives=false&textReferences=false&py=3&rawInputLstJSON=%5B%5D&curInstr=6
[3]
http://www.pythontutor.com/visualize.html#code=a0+%3D+a1+%3D+%5B1,+2%5D%0Ab0+%3D+%5B1,+2%5D%0Ab1+%3D+%5B1,+2%5D%0Aa+%3D+%5Ba0,+a1%5D%0Ab+%3D+%5Bb0,+b1%5D%0Adel+a0,+a1,+b0,+b1%0Aa%5B0%5D%5B0%5D+%3D+%22Oops!%22&mode=display&origin=opt-frontend.js&cumulative=false&heapPrimitives=false&textReferences=false&py=3&rawInputLstJSON=%5B%5D&curInstr=7
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Re: Python handles globals badly. tdev@freenet.de - 2015-09-11 14:26 -0700
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-11 23:50 +0200
Re: Python handles globals badly. Michael Torrie <torriem@gmail.com> - 2015-09-11 18:01 -0600
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-12 07:22 +0200
Re: Python handles globals badly. MRAB <python@mrabarnett.plus.com> - 2015-09-12 18:05 +0100
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:04 +0200
Re: Python handles globals badly. Steven D'Aprano <steve@pearwood.info> - 2015-09-13 22:06 +1000
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:11 +0200
Re: Python handles globals badly. Ned Batchelder <ned@nedbatchelder.com> - 2015-09-13 05:17 -0700
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-15 05:36 +0200
Re: Python handles globals badly. Emile van Sebille <emile@fenx.com> - 2015-09-12 10:18 -0700
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:06 +0200
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:10 +0200
Re: Python handles globals badly. Michael Torrie <torriem@gmail.com> - 2015-09-12 20:32 -0600
Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:05 +0200
Re: Python handles globals badly. random832@fastmail.us - 2015-09-11 20:11 -0400
Re: Python handles globals badly. Michael Torrie <torriem@gmail.com> - 2015-09-11 18:34 -0600
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 03:57 +0100
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 04:01 +0100
Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 00:06 -0400
Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 00:16 -0400
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 05:17 +0100
Terminology: “reference” versus “pointer” (was: Python handles globals badly.) Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 14:27 +1000
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 05:34 +0100
Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 00:34 -0400
Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 00:42 -0400
Re: Terminology: “reference” versus “pointer” Steven D'Aprano <steve@pearwood.info> - 2015-09-13 02:32 +1000
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 09:54 -0700
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-13 03:06 +1000
Re: Terminology: "reference" versus "pointer" Emile van Sebille <emile@fenx.com> - 2015-09-12 10:14 -0700
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 03:24 +1000
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-13 03:34 +1000
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 05:45 +0100
Re: Terminology: “reference” versus “pointer” Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 14:52 +1000
Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 01:03 -0400
Re: Terminology: “reference” versus “pointer” Steven D'Aprano <steve@pearwood.info> - 2015-09-13 02:50 +1000
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 10:04 -0700
Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 01:07 -0400
Re: Terminology: “reference” versus “pointer” Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 15:20 +1000
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 06:25 +0100
Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 01:35 -0400
Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 01:42 -0400
Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 06:54 +0100
Re: Terminology: “reference” versus “pointer” Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:02 +1000
Re: Terminology: “reference” versus “pointer” Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 07:05 +0100
Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:13 +1000
Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 02:15 -0400
Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 02:25 -0400
Re: Terminology: “reference” versus “pointer” Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 16:26 +1000
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 05:46 -0700
Re: Terminology: "reference" versus "pointer" Laura Creighton <lac@openend.se> - 2015-09-12 16:41 +0200
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 08:13 -0700
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 09:17 -0700
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 10:12 -0700
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 04:14 +1000
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 03:48 +1000
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 11:45 -0700
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 22:50 +1000
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 23:29 +1000
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-13 18:34 -0700
Re: Terminology: "reference" versus "pointer" Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-14 04:34 +0100
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 12:58 -0700
Re: Terminology: "reference" versus "pointer" Emile van Sebille <emile@fenx.com> - 2015-09-12 15:14 -0700
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 15:34 -0700
Re: Terminology: "reference" versus "pointer" Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-13 00:14 +0100
Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-12 17:02 -0700
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 17:28 -0700
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 17:44 -0700
Re: Terminology: "reference" versus "pointer" Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-13 03:22 +0100
Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-12 19:25 -0700
Re: Terminology: "reference" versus "pointer" Michael Torrie <torriem@gmail.com> - 2015-09-12 20:35 -0600
Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-13 12:42 +1000
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-13 08:31 -0700
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 01:39 +1000
Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-14 06:48 +1000
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-13 18:13 -0700
Re: Terminology: "reference" versus "pointer" Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-09-13 12:32 -0400
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 17:23 -0700
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 16:39 -0700
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-13 10:19 +1000
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 17:25 -0700
Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 18:07 -0700
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-12 20:54 +0300
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 11:21 -0700
Re: Terminology: "reference" versus "pointer" Jussi Piitulainen <harvesting@makes.email.invalid> - 2015-09-12 23:02 +0300
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-12 17:10 -0400
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 12:30 +1000
Re: Terminology: "reference" versus "pointer" Jussi Piitulainen <harvesting@makes.email.invalid> - 2015-09-13 09:40 +0300
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-12 23:13 +0300
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-12 17:27 -0400
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-13 21:04 +0300
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 05:03 +1000
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-13 15:04 -0400
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 02:17 +0300
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-14 11:10 +1000
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 04:22 +0300
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-14 12:38 +1000
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 06:23 +0300
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-15 02:59 +1000
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 20:24 +0300
Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-14 11:29 -0700
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 22:30 +0300
Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-14 13:16 -0700
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 23:32 +0300
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 11:30 +1000
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 05:26 +0300
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 09:52 +1000
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 03:30 +0300
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 10:58 +1000
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-13 19:38 -0400
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 17:48 +0300
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 11:10 -0400
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-15 03:03 +1000
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 13:34 -0400
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-16 00:26 +1000
Re: Terminology: "reference" versus "pointer" Emile van Sebille <emile@fenx.com> - 2015-09-14 10:51 -0700
Re: Terminology: "reference" versus "pointer" Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-09-16 20:14 +1200
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-16 18:18 +1000
Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-16 18:24 +1000
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-16 18:33 +1000
Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-15 03:59 +1000
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 14:02 -0400
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-16 00:14 +1000
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 20:45 +0300
Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 14:00 -0400
Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 21:17 +0300
Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 03:08 +1000
Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 10:26 -0700
Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-13 11:13 +1000
Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:27 +1000
Re: Terminology: “reference” versus “pointer” Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:31 +1000
Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-11 16:10 -0600
Re: Python handles globals badly. MRAB <python@mrabarnett.plus.com> - 2015-09-12 00:03 +0100
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