Add a Python-like slice operator for lists and strings #983

justinfagnani · 2011-12-27T02:39:56Z

String.substring() and List.getRange() are somewhat verbose, but very common operations. Python's slice operator provides an easy-to-read notation to replace these.

Examples of substring() and slice [:]

string.substring(a) -> string[a:]

string.substring(a, b) -> string[a:b]

string.substring(0, a) -> string[:a]

dgrove · 2012-01-02T19:31:14Z

Removed Type-Defect label.
Added Type-Enhancement, Area-Library, Triaged labels.

DartBot · 2012-01-16T14:17:29Z

This comment was originally written by @jinmingjian

great. more my idea is to enhance the slicing operator to an general indexing technology for array like objects, like:

1: a:b = a:1:b = a,a+1,...,b
2: a:2:b = a, a+2,...b
3: a:-1:b = a, a-1,...b
4: [:,a:b] = [1,a:b],[2,a:b]...

DartBot · 2012-01-18T12:15:42Z

This comment was originally written by thebinarysearc...@gmail.com

I would argue that it is not easier to read. substring says what it is doing in English, whereas string[3:2] is symbolism.

DartBot · 2012-01-18T14:34:46Z

This comment was originally written by @jinmingjian

yes or no. Yes, because this is just a syntax magic. No, ":" for slicing is the tradition of numerical computing software[1]. My suggestion is more mathematical. That is, it does not pursue symbolism, it pursues intuition. The ":" is used for generating a vectorized index(i.e.,1D array). And,

the basic form is [start:step:end];
[start:end] is the simplified form of [start:1:end];
: is the simplified form of [head:tail];
generally, start<=end and step>0, but allow start>=end and step<0 makes reversed indexing easier.
get nothing if the index does not exist mathematically.

So,
[3:2] -> [3:1:2], 3 can not reach 2 by step 1 -> nothig. may want [3:-1:2]
[:a] -> not syntax right, may want [0:a]

[1] http://en.wikipedia.org/wiki/Array_slicing

DartBot · 2012-01-18T14:35:28Z

This comment was originally written by @jinmingjian

numerical computing software -> numerical computing language, more exactly.

DartBot · 2012-01-19T14:20:59Z

This comment was originally written by @seaneagan

I think this would require a user-definable operator:

List#getRange becomes:
List<T> operator [:]([int first, int last]);

String#substring becomes:
String operator [:]([int first, int last]);

And it would probably make sense to support slicing then as well, by replacing List#setRange with:

List<T> operator [:]= (List other, [int first, int last]);

List#removeRange also becomes unnecessary, instead of:

list.removeRange(0, 5);

just do:

list[:5] = [];
// or
list[:5] = null;

floitschG · 2012-12-18T17:36:44Z

Reassigning to language. This requires new syntax and is thus not a library bug.

Removed Area-Library label.
Added Area-Language label.

floitschG · 2013-03-08T23:19:08Z

Issue #8977 has been merged into this issue.

Zectbumo · 2014-08-01T07:55:26Z

Please support negative indexes (relative from the end) as Python does.
At the very least make String.substring() accept negative indexes.

gbracha · 2014-08-28T00:03:18Z

Set owner to @gbracha.
Removed Priority-Medium label.
Added Priority-Low, Accepted labels.

deadsoul44 · 2020-03-06T17:02:29Z

It has been 8.5 years. substring method should accept negative values.

Zectbumo · 2020-03-06T17:27:33Z

Yeah, this is really weird since even Javascript String.prototype.slice() takes negative values.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice

pauleohare · 2020-04-28T11:32:02Z

Any news on this? Is it ever going to happen? Doesn't sound too difficult. Is it?

2021-01-24 irina.arkhipets@gmail.com Issue #983: Static warning checks corrected. 2021-01-22 irina.arkhipets@gmail.com Issue #983: triple-shift folders re-named correctly, typo in the library paths updated for 2 tests. 2021-01-21 sgrekhov@unipro.ru Fixes #985. LateInitializationError removed 2021-01-20 sgrekhov@unipro.ru Fixes #982. Add tests for The future value type of an asynchronous non-generator function part of NNBD spec 2021-01-19 irina.arkhipets@gmail.com Issue #462: NNBD type-normalization tests for weak mode added. 2021-01-19 irina.arkhipets@gmail.com Issue #462: NNBD type-aliases tests for weak mode added. 2021-01-19 irina.arkhipets@gmail.com Issue #462: NNBD tripple-shift tests for weak mode added. 2021-01-19 irina.arkhipets@gmail.com Issue #462: NNBD tests for weak mode added for the override checkings. 2021-01-19 irina.arkhipets@gmail.com Issue #462: NNBD tests for weak mode added (Leatest-greatest-closures). 2021-01-19 irina.arkhipets@gmail.com Issue #462: NNBD tests for weak mode added (Leatest-greatest-closures). 2021-01-18 sgrekhov@unipro.ru Fixes #981. Add tests for Return statements part of NNBD spec 2021-01-18 irina.arkhipets@gmail.com Issue #462: NNBD tests for weak mode corrected according to the current Spec changes. 2021-01-14 irina.arkhipets@gmail.com Issue #462: Additional comments regarding the constant evaluation issues added to weak mode tests. 2021-01-14 sgrekhov@unipro.ru Fixes #980. Remove warnings expectations for overriding default values of optional parameters tests 2021-01-13 irina.arkhipets@gmail.com Issue #462: Tests for weak mode added to nnbd/weak/flow-analysis directory. 2021-01-12 sgrekhov@unipro.ru #978. Weak mode test changes 2021-01-12 irina.arkhipets@gmail.com Issue #462: Tests for weak mode added to nnbd/weak directory. 2021-01-11 sgrekhov@unipro.ru Fixes #978. Tests updated according to the "flow analysis boolean variable" feature 2020-12-25 irina.arkhipets@gmail.com Issues #463: Tests for weak mode added. 2020-12-25 irina.arkhipets@gmail.com Issues #462, #463: Moved or added new nnbd tests for weak mode, added new tests for strong mode. 2020-12-24 sgrekhov@unipro.ru #970. Usr correct values for ProcessSignal.sigusr1 and ProcessSignal.sigusr2 on Mac 2020-12-24 irina.arkhipets@gmail.com Issue #462: 1. Added nnbd tests for weak mode: exports_*, expression_typing_*, extension_method_resolution_*, future_flattening_*. 2. Moved and re-factored nnbd extension_method_resolution_*, future_flattening_* tests for weak mode into weak folder. 3. Copyrights updated Issue #463: Two exports* tests for strong mode added. 2020-12-24 sgrekhov@unipro.ru Fixes #496. Change tested date to 1 second instead of 1 day to reduce probability to change timezone on DST 2020-12-23 sgrekhov@unipro.ru Fixes #473. Remove UtilsHtml directory 2020-12-23 irina.arkhipets@gmail.com Fix for Issue #462: 1. Added nnbd tests for weak mode: assignability_*, const_evaluation_*, const_objects_*, const_type_var_elimination_*. 2. Moved and re-factored nnbd exports_* tests for weak mode into weak folder. 2020-12-10 sgrekhov@unipro.ru Fixes #976. Remove obsolete errors expectations 2020-12-10 sgrekhov@unipro.ru Fixes #975. Fix wrong expected compile time error type 2020-12-07 sgrekhov@unipro.ru Flag Requirements=nnbd-weak added to the tests that run legacy code Cq-Include-Trybots: dart/try:analyzer-nnbd-linux-release-try,dart2js-nnbd-linux-x64-chrome-try,ddc-nnbd-linux-release-chrome-try,front-end-nnbd-linux-release-x64-try,vm-kernel-nnbd-linux-release-simarm64-try,vm-kernel-nnbd-linux-release-x64-try,vm-kernel-nnbd-mac-release-x64-try,vm-kernel-nnbd-win-release-x64-try,vm-kernel-precomp-nnbd-linux-release-x64-try Change-Id: I69acc5c0a28fd2e7a2d38f6c9062e5a5854bdfa6 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/180823 Reviewed-by: William Hesse <whesse@google.com>

jabbalaci · 2021-05-16T19:36:46Z

Any update? Will it be added to the language?

mraleph · 2021-05-17T09:35:17Z

Any update? Will it be added to the language?

By default the answer to this sort of question is: there is no update and there are no immediate plans to add it to the language.

If there was any sort of update it would be posted here. Language features which are being worked on are part of the language funnel.

jabbalaci · 2021-05-17T09:37:21Z

@mraleph Thanks. Then maybe this issue could be closed.

justinfagnani added Type-Enhancement P3 A lower priority bug or feature request area-language Dart language related items (some items might be better tracked at github.com/dart-lang/language). labels Aug 28, 2014

justinfagnani assigned gbracha Aug 28, 2014

DartBot mentioned this issue Jun 4, 2015

Add slice/slice-assignment operators. #8977

Closed

kevmoo added type-enhancement A request for a change that isn't a bug and removed accepted type-enhancement A request for a change that isn't a bug labels Feb 29, 2016

munificent unassigned gbracha Jan 3, 2017

lrhn added the core-m label Dec 6, 2018

lrhn added this to Non-Breaking and Complex in Language Enhancement Categories Dec 14, 2018

vsmenon mentioned this issue Apr 24, 2019

We hope to add python slice-like functionality in the next release #36703

Closed

lrhn removed the P3 A lower priority bug or feature request label Oct 14, 2019

mateusfccp mentioned this issue Jun 23, 2023

Support Python-like negative indexes on indexed collections-like objects #52771

Open

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Add a Python-like slice operator for lists and strings #983

Add a Python-like slice operator for lists and strings #983

justinfagnani commented Dec 27, 2011

dgrove commented Jan 2, 2012

DartBot commented Jan 16, 2012 •

edited by munificent

DartBot commented Jan 18, 2012

DartBot commented Jan 18, 2012

DartBot commented Jan 18, 2012

DartBot commented Jan 19, 2012

floitschG commented Dec 18, 2012

floitschG commented Mar 8, 2013

Zectbumo commented Aug 1, 2014

gbracha commented Aug 28, 2014

deadsoul44 commented Mar 6, 2020

Zectbumo commented Mar 6, 2020

pauleohare commented Apr 28, 2020

jabbalaci commented May 16, 2021

mraleph commented May 17, 2021

jabbalaci commented May 17, 2021

Add a Python-like slice operator for lists and strings #983

Add a Python-like slice operator for lists and strings #983

Comments

justinfagnani commented Dec 27, 2011

dgrove commented Jan 2, 2012

DartBot commented Jan 16, 2012 • edited by munificent

DartBot commented Jan 18, 2012

DartBot commented Jan 18, 2012

DartBot commented Jan 18, 2012

DartBot commented Jan 19, 2012

floitschG commented Dec 18, 2012

floitschG commented Mar 8, 2013

Zectbumo commented Aug 1, 2014

gbracha commented Aug 28, 2014

deadsoul44 commented Mar 6, 2020

Zectbumo commented Mar 6, 2020

pauleohare commented Apr 28, 2020

jabbalaci commented May 16, 2021

mraleph commented May 17, 2021

jabbalaci commented May 17, 2021

DartBot commented Jan 16, 2012 •

edited by munificent