-
Notifications
You must be signed in to change notification settings - Fork 7
/
nep-0004-datetime-proposal3.html
1257 lines (1038 loc) · 103 KB
/
nep-0004-datetime-proposal3.html
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
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html>
<html lang="en" data-content_root="./" >
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
<title>NEP 4 — A (third) proposal for implementing some date/time types in NumPy — NumPy Enhancement Proposals</title>
<script data-cfasync="false">
document.documentElement.dataset.mode = localStorage.getItem("mode") || "";
document.documentElement.dataset.theme = localStorage.getItem("theme") || "";
</script>
<!-- Loaded before other Sphinx assets -->
<link href="_static/styles/theme.css?digest=3ee479438cf8b5e0d341" rel="stylesheet" />
<link href="_static/styles/bootstrap.css?digest=3ee479438cf8b5e0d341" rel="stylesheet" />
<link href="_static/styles/pydata-sphinx-theme.css?digest=3ee479438cf8b5e0d341" rel="stylesheet" />
<link href="_static/vendor/fontawesome/6.5.2/css/all.min.css?digest=3ee479438cf8b5e0d341" rel="stylesheet" />
<link rel="preload" as="font" type="font/woff2" crossorigin href="_static/vendor/fontawesome/6.5.2/webfonts/fa-solid-900.woff2" />
<link rel="preload" as="font" type="font/woff2" crossorigin href="_static/vendor/fontawesome/6.5.2/webfonts/fa-brands-400.woff2" />
<link rel="preload" as="font" type="font/woff2" crossorigin href="_static/vendor/fontawesome/6.5.2/webfonts/fa-regular-400.woff2" />
<link rel="stylesheet" type="text/css" href="_static/pygments.css?v=fa44fd50" />
<!-- Pre-loaded scripts that we'll load fully later -->
<link rel="preload" as="script" href="_static/scripts/bootstrap.js?digest=3ee479438cf8b5e0d341" />
<link rel="preload" as="script" href="_static/scripts/pydata-sphinx-theme.js?digest=3ee479438cf8b5e0d341" />
<script src="_static/vendor/fontawesome/6.5.2/js/all.min.js?digest=3ee479438cf8b5e0d341"></script>
<script src="_static/documentation_options.js?v=7f41d439"></script>
<script src="_static/doctools.js?v=888ff710"></script>
<script src="_static/sphinx_highlight.js?v=dc90522c"></script>
<script>DOCUMENTATION_OPTIONS.pagename = 'nep-0004-datetime-proposal3';</script>
<link rel="icon" href="_static/favicon.ico"/>
<link rel="index" title="Index" href="genindex.html" />
<link rel="search" title="Search" href="search.html" />
<link rel="next" title="NEP 6 — Replacing Trac with a different bug tracker" href="nep-0006-newbugtracker.html" />
<link rel="prev" title="NEP 3 — Cleaning the math configuration of numpy.core" href="nep-0003-math_config_clean.html" />
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<meta name="docsearch:language" content="en"/>
<meta name="docbuild:last-update" content="Jun 05, 2024"/>
</head>
<body data-bs-spy="scroll" data-bs-target=".bd-toc-nav" data-offset="180" data-bs-root-margin="0px 0px -60%" data-default-mode="">
<div id="pst-skip-link" class="skip-link d-print-none"><a href="#main-content">Skip to main content</a></div>
<div id="pst-scroll-pixel-helper"></div>
<button type="button" class="btn rounded-pill" id="pst-back-to-top">
<i class="fa-solid fa-arrow-up"></i>Back to top</button>
<input type="checkbox"
class="sidebar-toggle"
id="pst-primary-sidebar-checkbox"/>
<label class="overlay overlay-primary" for="pst-primary-sidebar-checkbox"></label>
<input type="checkbox"
class="sidebar-toggle"
id="pst-secondary-sidebar-checkbox"/>
<label class="overlay overlay-secondary" for="pst-secondary-sidebar-checkbox"></label>
<div class="search-button__wrapper">
<div class="search-button__overlay"></div>
<div class="search-button__search-container">
<form class="bd-search d-flex align-items-center"
action="search.html"
method="get">
<i class="fa-solid fa-magnifying-glass"></i>
<input type="search"
class="form-control"
name="q"
id="search-input"
placeholder="Search the docs ..."
aria-label="Search the docs ..."
autocomplete="off"
autocorrect="off"
autocapitalize="off"
spellcheck="false"/>
<span class="search-button__kbd-shortcut"><kbd class="kbd-shortcut__modifier">Ctrl</kbd>+<kbd>K</kbd></span>
</form></div>
</div>
<div class="pst-async-banner-revealer d-none">
<aside id="bd-header-version-warning" class="d-none d-print-none" aria-label="Version warning"></aside>
</div>
<header class="bd-header navbar navbar-expand-lg bd-navbar d-print-none">
<div class="bd-header__inner bd-page-width">
<button class="sidebar-toggle primary-toggle" aria-label="Site navigation">
<span class="fa-solid fa-bars"></span>
</button>
<div class="col-lg-3 navbar-header-items__start">
<div class="navbar-item">
<a class="navbar-brand logo" href="content.html">
<img src="_static/numpylogo.svg" class="logo__image only-light" alt="NumPy Enhancement Proposals - Home"/>
<script>document.write(`<img src="_static/numpylogo.svg" class="logo__image only-dark" alt="NumPy Enhancement Proposals - Home"/>`);</script>
</a></div>
</div>
<div class="col-lg-9 navbar-header-items">
<div class="me-auto navbar-header-items__center">
<div class="navbar-item">
<nav class="navbar-nav">
<ul class="bd-navbar-elements navbar-nav">
<li class="nav-item pst-header-nav-item current active">
<a class="nav-link nav-internal" href="index.html">
Index
</a>
</li>
<li class="nav-item pst-header-nav-item">
<a class="nav-link nav-internal" href="scope.html">
The Scope of NumPy
</a>
</li>
<li class="nav-item pst-header-nav-item">
<a class="nav-link nav-internal" href="roadmap.html">
Current roadmap
</a>
</li>
<li class="nav-item pst-header-nav-item">
<a class="nav-link nav-external" href="https://github.com/numpy/numpy/issues?q=is%3Aopen+is%3Aissue+label%3A%2223+-+Wish+List%22">
Wishlist
</a>
</li>
</ul>
</nav></div>
</div>
<div class="navbar-header-items__end">
<div class="navbar-item navbar-persistent--container">
<script>
document.write(`
<button class="btn navbar-btn search-button-field search-button__button" title="Search" aria-label="Search" data-bs-placement="bottom" data-bs-toggle="tooltip">
<i class="fa-solid fa-magnifying-glass"></i>
<span class="search-button__default-text">Search</span>
<span class="search-button__kbd-shortcut"><kbd class="kbd-shortcut__modifier">Ctrl</kbd>+<kbd class="kbd-shortcut__modifier">K</kbd></span>
</button>
`);
</script>
</div>
<div class="navbar-item">
<script>
document.write(`
<button class="btn btn-sm navbar-btn theme-switch-button" title="light/dark" aria-label="light/dark" data-bs-placement="bottom" data-bs-toggle="tooltip">
<span class="theme-switch nav-link" data-mode="light"><i class="fa-solid fa-sun fa-lg"></i></span>
<span class="theme-switch nav-link" data-mode="dark"><i class="fa-solid fa-moon fa-lg"></i></span>
<span class="theme-switch nav-link" data-mode="auto"><i class="fa-solid fa-circle-half-stroke fa-lg"></i></span>
</button>
`);
</script></div>
<div class="navbar-item"><ul class="navbar-icon-links navbar-nav"
aria-label="Icon Links">
<li class="nav-item">
<a href="https://github.com/numpy/numpy" title="GitHub" class="nav-link" rel="noopener" target="_blank" data-bs-toggle="tooltip" data-bs-placement="bottom"><span><i class="fa-brands fa-square-github fa-lg" aria-hidden="true"></i></span>
<span class="sr-only">GitHub</span></a>
</li>
</ul></div>
</div>
</div>
<div class="navbar-persistent--mobile">
<script>
document.write(`
<button class="btn navbar-btn search-button-field search-button__button" title="Search" aria-label="Search" data-bs-placement="bottom" data-bs-toggle="tooltip">
<i class="fa-solid fa-magnifying-glass"></i>
<span class="search-button__default-text">Search</span>
<span class="search-button__kbd-shortcut"><kbd class="kbd-shortcut__modifier">Ctrl</kbd>+<kbd class="kbd-shortcut__modifier">K</kbd></span>
</button>
`);
</script>
</div>
<button class="sidebar-toggle secondary-toggle" aria-label="On this page">
<span class="fa-solid fa-outdent"></span>
</button>
</div>
</header>
<div class="bd-container">
<div class="bd-container__inner bd-page-width">
<div class="bd-sidebar-primary bd-sidebar">
<div class="sidebar-header-items sidebar-primary__section">
<div class="sidebar-header-items__center">
<div class="navbar-item">
<nav class="navbar-nav">
<ul class="bd-navbar-elements navbar-nav">
<li class="nav-item pst-header-nav-item current active">
<a class="nav-link nav-internal" href="index.html">
Index
</a>
</li>
<li class="nav-item pst-header-nav-item">
<a class="nav-link nav-internal" href="scope.html">
The Scope of NumPy
</a>
</li>
<li class="nav-item pst-header-nav-item">
<a class="nav-link nav-internal" href="roadmap.html">
Current roadmap
</a>
</li>
<li class="nav-item pst-header-nav-item">
<a class="nav-link nav-external" href="https://github.com/numpy/numpy/issues?q=is%3Aopen+is%3Aissue+label%3A%2223+-+Wish+List%22">
Wishlist
</a>
</li>
</ul>
</nav></div>
</div>
<div class="sidebar-header-items__end">
<div class="navbar-item">
<script>
document.write(`
<button class="btn btn-sm navbar-btn theme-switch-button" title="light/dark" aria-label="light/dark" data-bs-placement="bottom" data-bs-toggle="tooltip">
<span class="theme-switch nav-link" data-mode="light"><i class="fa-solid fa-sun fa-lg"></i></span>
<span class="theme-switch nav-link" data-mode="dark"><i class="fa-solid fa-moon fa-lg"></i></span>
<span class="theme-switch nav-link" data-mode="auto"><i class="fa-solid fa-circle-half-stroke fa-lg"></i></span>
</button>
`);
</script></div>
<div class="navbar-item"><ul class="navbar-icon-links navbar-nav"
aria-label="Icon Links">
<li class="nav-item">
<a href="https://github.com/numpy/numpy" title="GitHub" class="nav-link" rel="noopener" target="_blank" data-bs-toggle="tooltip" data-bs-placement="bottom"><span><i class="fa-brands fa-square-github fa-lg" aria-hidden="true"></i></span>
<span class="sr-only">GitHub</span></a>
</li>
</ul></div>
</div>
</div>
<div class="sidebar-primary-items__start sidebar-primary__section">
<div class="sidebar-primary-item">
<nav class="bd-docs-nav bd-links"
aria-label="Section Navigation">
<p class="bd-links__title" role="heading" aria-level="1">Section Navigation</p>
<div class="bd-toc-item navbar-nav"><ul class="nav bd-sidenav">
<li class="toctree-l1"><a class="reference internal" href="scope.html">The Scope of NumPy</a></li>
<li class="toctree-l1"><a class="reference internal" href="roadmap.html">Current roadmap</a></li>
<li class="toctree-l1"><a class="reference external" href="https://github.com/numpy/numpy/issues?q=is%3Aopen+is%3Aissue+label%3A%2223+-+Wish+List%22">Wish list</a></li>
</ul>
<ul class="current nav bd-sidenav">
<li class="toctree-l1 has-children"><a class="reference internal" href="meta.html">Meta-NEPs (NEPs about NEPs or active Processes)</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="nep-0000.html">NEP 0 — Purpose and process</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0023-backwards-compatibility.html">NEP 23 — Backwards compatibility and deprecation policy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0036-fair-play.html">NEP 36 — Fair play</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0045-c_style_guide.html">NEP 45 — C style guide</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0046-sponsorship-guidelines.html">NEP 46 — NumPy sponsorship guidelines</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0048-spending-project-funds.html">NEP 48 — Spending NumPy project funds</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-template.html">NEP X — Template and instructions</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="provisional.html">Provisional NEPs (provisionally accepted; interface may change)</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul class="simple">
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="accepted.html">Accepted NEPs (implementation in progress)</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="nep-0041-improved-dtype-support.html">NEP 41 — First step towards a new datatype system</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0042-new-dtypes.html">NEP 42 — New and extensible DTypes</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0044-restructuring-numpy-docs.html">NEP 44 — Restructuring the NumPy documentation</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0051-scalar-representation.html">NEP 51 — Changing the representation of NumPy scalars</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0052-python-api-cleanup.html">NEP 52 — Python API cleanup for NumPy 2.0</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="open.html">Open NEPs (under consideration)</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="nep-0043-extensible-ufuncs.html">NEP 43 — Enhancing the extensibility of UFuncs</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0050-scalar-promotion.html">NEP 50 — Promotion rules for Python scalars</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0053-c-abi-evolution.html">NEP 53 — Evolving the NumPy C-API for NumPy 2.0</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0054-simd-cpp-highway.html">NEP 54 — SIMD infrastructure evolution: adopting Google Highway when moving to C++?</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="finished.html">Finished NEPs</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="nep-0001-npy-format.html">NEP 1 — A simple file format for NumPy arrays</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0005-generalized-ufuncs.html">NEP 5 — Generalized universal functions</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0007-datetime-proposal.html">NEP 7 — A proposal for implementing some date/time types in NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0010-new-iterator-ufunc.html">NEP 10 — Optimizing iterator/UFunc performance</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0013-ufunc-overrides.html">NEP 13 — A mechanism for overriding Ufuncs</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0014-dropping-python2.7-proposal.html">NEP 14 — Plan for dropping Python 2.7 support</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0015-merge-multiarray-umath.html">NEP 15 — Merging multiarray and umath</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0018-array-function-protocol.html">NEP 18 — A dispatch mechanism for NumPy's high level array functions</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0019-rng-policy.html">NEP 19 — Random number generator policy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0020-gufunc-signature-enhancement.html">NEP 20 — Expansion of generalized universal function signatures</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0022-ndarray-duck-typing-overview.html">NEP 22 — Duck typing for NumPy arrays – high level overview</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0027-zero-rank-arrarys.html">NEP 27 — Zero rank arrays</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0028-website-redesign.html">NEP 28 — numpy.org website redesign</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0029-deprecation_policy.html">NEP 29 — Recommend Python and NumPy version support as a community policy standard</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0032-remove-financial-functions.html">NEP 32 — Remove the financial functions from NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0034-infer-dtype-is-object.html">NEP 34 — Disallow inferring ``dtype=object`` from sequences</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0035-array-creation-dispatch-with-array-function.html">NEP 35 — Array creation dispatching with __array_function__</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0038-SIMD-optimizations.html">NEP 38 — Using SIMD optimization instructions for performance</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0040-legacy-datatype-impl.html">NEP 40 — Legacy datatype implementation in NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0049.html">NEP 49 — Data allocation strategies</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0055-string_dtype.html">NEP 55 — Add a UTF-8 variable-width string DType to NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0056-array-api-main-namespace.html">NEP 56 — Array API standard support in NumPy's main namespace</a></li>
</ul>
</details></li>
<li class="toctree-l1 current active has-children"><a class="reference internal" href="deferred.html">Deferred and Superseded NEPs</a><details open="open"><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="nep-0002-warnfix.html">NEP 2 — A proposal to build numpy without warning with a big set of warning flags</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0003-math_config_clean.html">NEP 3 — Cleaning the math configuration of numpy.core</a></li>
<li class="toctree-l2 current active"><a class="current reference internal" href="#">NEP 4 — A (third) proposal for implementing some date/time types in NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0006-newbugtracker.html">NEP 6 — Replacing Trac with a different bug tracker</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0008-groupby_additions.html">NEP 8 — A proposal for adding groupby functionality to NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0009-structured_array_extensions.html">NEP 9 — Structured array extensions</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0011-deferred-ufunc-evaluation.html">NEP 11 — Deferred UFunc evaluation</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0012-missing-data.html">NEP 12 — Missing data functionality in NumPy</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0021-advanced-indexing.html">NEP 21 — Simplified and explicit advanced indexing</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0024-missing-data-2.html">NEP 24 — Missing data functionality - alternative 1 to NEP 12</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0025-missing-data-3.html">NEP 25 — NA support via special dtypes</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0026-missing-data-summary.html">NEP 26 — Summary of missing data NEPs and discussion</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0030-duck-array-protocol.html">NEP 30 — Duck typing for NumPy arrays - implementation</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0031-uarray.html">NEP 31 — Context-local and global overrides of the NumPy API</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0037-array-module.html">NEP 37 — A dispatch protocol for NumPy-like modules</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0047-array-api-standard.html">NEP 47 — Adopting the array API standard</a></li>
</ul>
</details></li>
<li class="toctree-l1 has-children"><a class="reference internal" href="rejected.html">Rejected and Withdrawn NEPs</a><details><summary><span class="toctree-toggle" role="presentation"><i class="fa-solid fa-chevron-down"></i></span></summary><ul>
<li class="toctree-l2"><a class="reference internal" href="nep-0016-abstract-array.html">NEP 16 — An abstract base class for identifying "duck arrays"</a></li>
<li class="toctree-l2"><a class="reference internal" href="nep-0017-split-out-maskedarray.html">NEP 17 — Split out masked arrays</a></li>
</ul>
</details></li>
</ul>
</div>
</nav></div>
</div>
<div class="sidebar-primary-items__end sidebar-primary__section">
</div>
<div id="rtd-footer-container"></div>
</div>
<main id="main-content" class="bd-main" role="main">
<div class="bd-content">
<div class="bd-article-container">
<div class="bd-header-article d-print-none">
<div class="header-article-items header-article__inner">
<div class="header-article-items__start">
<div class="header-article-item">
<nav aria-label="Breadcrumb" class="d-print-none">
<ul class="bd-breadcrumbs">
<li class="breadcrumb-item breadcrumb-home">
<a href="content.html" class="nav-link" aria-label="Home">
<i class="fa-solid fa-home"></i>
</a>
</li>
<li class="breadcrumb-item"><a href="index.html" class="nav-link">Roadmap & NumPy enhancement proposals</a></li>
<li class="breadcrumb-item"><a href="deferred.html" class="nav-link">Deferred and Superseded NEPs</a></li>
<li class="breadcrumb-item active" aria-current="page">NEP 4 — A...</li>
</ul>
</nav>
</div>
</div>
</div>
</div>
<div id="searchbox"></div>
<article class="bd-article">
<section id="nep-4-a-third-proposal-for-implementing-some-date-time-types-in-numpy">
<span id="nep04"></span><h1>NEP 4 — A (third) proposal for implementing some date/time types in NumPy<a class="headerlink" href="#nep-4-a-third-proposal-for-implementing-some-date-time-types-in-numpy" title="Link to this heading">#</a></h1>
<dl class="field-list simple">
<dt class="field-odd">Author<span class="colon">:</span></dt>
<dd class="field-odd"><p>Francesc Alted i Abad</p>
</dd>
<dt class="field-even">Contact<span class="colon">:</span></dt>
<dd class="field-even"><p><a class="reference external" href="mailto:faltet%40pytables.com">faltet<span>@</span>pytables<span>.</span>com</a></p>
</dd>
<dt class="field-odd">Author<span class="colon">:</span></dt>
<dd class="field-odd"><p>Ivan Vilata i Balaguer</p>
</dd>
<dt class="field-even">Contact<span class="colon">:</span></dt>
<dd class="field-even"><p><a class="reference external" href="mailto:ivan%40selidor.net">ivan<span>@</span>selidor<span>.</span>net</a></p>
</dd>
<dt class="field-odd">Date<span class="colon">:</span></dt>
<dd class="field-odd"><p>2008-07-30</p>
</dd>
<dt class="field-even">Status<span class="colon">:</span></dt>
<dd class="field-even"><p>Deferred</p>
</dd>
</dl>
<section id="executive-summary">
<h2>Executive summary<a class="headerlink" href="#executive-summary" title="Link to this heading">#</a></h2>
<p>A date/time mark is something very handy to have in many fields where
one has to deal with data sets. While Python has several modules that
define a date/time type (like the integrated <code class="docutils literal notranslate"><span class="pre">datetime</span></code> <a class="footnote-reference brackets" href="#id10" id="id1" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a> or
<code class="docutils literal notranslate"><span class="pre">mx.DateTime</span></code> <a class="footnote-reference brackets" href="#id11" id="id2" role="doc-noteref"><span class="fn-bracket">[</span>2<span class="fn-bracket">]</span></a>), NumPy has a lack of them.</p>
<p>In this document, we are proposing the addition of a series of date/time
types to fill this gap. The requirements for the proposed types are
two-folded: 1) they have to be fast to operate with and 2) they have to
be as compatible as possible with the existing <code class="docutils literal notranslate"><span class="pre">datetime</span></code> module that
comes with Python.</p>
</section>
<section id="types-proposed">
<h2>Types proposed<a class="headerlink" href="#types-proposed" title="Link to this heading">#</a></h2>
<p>To start with, it is virtually impossible to come up with a single
date/time type that fills the needs of every case of use. So, after
pondering about different possibilities, we have stuck with <em>two</em>
different types, namely <code class="docutils literal notranslate"><span class="pre">datetime64</span></code> and <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code> (these names
are preliminary and can be changed), that can have different time units
so as to cover different needs.</p>
<div class="admonition important">
<p class="admonition-title">Important</p>
<p>the time unit is conceived here as metadata that
<em>complements</em> a date/time dtype, <em>without changing the base type</em>. It
provides information about the <em>meaning</em> of the stored numbers, not
about their <em>structure</em>.</p>
</div>
<p>Now follows a detailed description of the proposed types.</p>
<section id="datetime64">
<h3><code class="docutils literal notranslate"><span class="pre">datetime64</span></code><a class="headerlink" href="#datetime64" title="Link to this heading">#</a></h3>
<p>It represents a time that is absolute (i.e. not relative). It is
implemented internally as an <code class="docutils literal notranslate"><span class="pre">int64</span></code> type. The internal epoch is the
POSIX epoch (see <a class="footnote-reference brackets" href="#id12" id="id3" role="doc-noteref"><span class="fn-bracket">[</span>3<span class="fn-bracket">]</span></a>). Like POSIX, the representation of a date
doesn’t take leap seconds into account.</p>
<p>In time unit <em>conversions</em> and time <em>representations</em> (but not in other
time computations), the value -2**63 (0x8000000000000000) is interpreted
as an invalid or unknown date, <em>Not a Time</em> or <em>NaT</em>. See the section
on time unit conversions for more information.</p>
<section id="time-units">
<h4>Time units<a class="headerlink" href="#time-units" title="Link to this heading">#</a></h4>
<p>It accepts different time units, each of them implying a different time
span. The table below describes the time units supported with their
corresponding time spans.</p>
<div class="pst-scrollable-table-container"><table class="table">
<thead>
<tr class="row-odd"><th class="head" colspan="2"><p>Time unit</p></th>
<th class="head"><p>Time span (years)</p></th>
</tr>
<tr class="row-even"><th class="head"><p>Code</p></th>
<th class="head"><p>Meaning</p></th>
<th class="head"></th>
</tr>
</thead>
<tbody>
<tr class="row-odd"><td><p>Y</p></td>
<td><p>year</p></td>
<td><p>[9.2e18 BC, 9.2e18 AD]</p></td>
</tr>
<tr class="row-even"><td><p>M</p></td>
<td><p>month</p></td>
<td><p>[7.6e17 BC, 7.6e17 AD]</p></td>
</tr>
<tr class="row-odd"><td><p>W</p></td>
<td><p>week</p></td>
<td><p>[1.7e17 BC, 1.7e17 AD]</p></td>
</tr>
<tr class="row-even"><td><p>B</p></td>
<td><p>business day</p></td>
<td><p>[3.5e16 BC, 3.5e16 AD]</p></td>
</tr>
<tr class="row-odd"><td><p>D</p></td>
<td><p>day</p></td>
<td><p>[2.5e16 BC, 2.5e16 AD]</p></td>
</tr>
<tr class="row-even"><td><p>h</p></td>
<td><p>hour</p></td>
<td><p>[1.0e15 BC, 1.0e15 AD]</p></td>
</tr>
<tr class="row-odd"><td><p>m</p></td>
<td><p>minute</p></td>
<td><p>[1.7e13 BC, 1.7e13 AD]</p></td>
</tr>
<tr class="row-even"><td><p>s</p></td>
<td><p>second</p></td>
<td><p>[ 2.9e9 BC, 2.9e9 AD]</p></td>
</tr>
<tr class="row-odd"><td><p>ms</p></td>
<td><p>millisecond</p></td>
<td><p>[ 2.9e6 BC, 2.9e6 AD]</p></td>
</tr>
<tr class="row-even"><td><p>us</p></td>
<td><p>microsecond</p></td>
<td><p>[290301 BC, 294241 AD]</p></td>
</tr>
<tr class="row-odd"><td><p>c#</p></td>
<td><p>ticks (100ns)</p></td>
<td><p>[ 2757 BC, 31197 AD]</p></td>
</tr>
<tr class="row-even"><td><p>ns</p></td>
<td><p>nanosecond</p></td>
<td><p>[ 1678 AD, 2262 AD]</p></td>
</tr>
</tbody>
</table>
</div>
<p>The value of an absolute date is thus <em>an integer number of units of the
chosen time unit</em> passed since the internal epoch. When working with
business days, Saturdays and Sundays are simply ignored from the count
(i.e. day 3 in business days is not Saturday 1970-01-03, but Monday
1970-01-05).</p>
</section>
<section id="building-a-datetime64-dtype">
<h4>Building a <code class="docutils literal notranslate"><span class="pre">datetime64</span></code> dtype<a class="headerlink" href="#building-a-datetime64-dtype" title="Link to this heading">#</a></h4>
<p>The proposed ways to specify the time unit in the dtype constructor are:</p>
<p>Using the long string notation:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">dtype</span><span class="p">(</span><span class="s1">'datetime64[us]'</span><span class="p">)</span>
</pre></div>
</div>
<p>Using the short string notation:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">dtype</span><span class="p">(</span><span class="s1">'M8[us]'</span><span class="p">)</span>
</pre></div>
</div>
<p>The default is microseconds if no time unit is specified. Thus, ‘M8’ is equivalent to ‘M8[us]’</p>
</section>
<section id="setting-and-getting-values">
<h4>Setting and getting values<a class="headerlink" href="#setting-and-getting-values" title="Link to this heading">#</a></h4>
<p>The objects with this dtype can be set in a series of ways:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s1">'M8[s]'</span><span class="p">)</span>
<span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">1199164176</span> <span class="c1"># assign to July 30th, 2008 at 17:31:00</span>
<span class="n">t</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="mi">2008</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">30</span><span class="p">,</span> <span class="mi">17</span><span class="p">,</span> <span class="mi">31</span><span class="p">,</span> <span class="mi">01</span><span class="p">)</span> <span class="c1"># with datetime module</span>
<span class="n">t</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'2008-07-30T17:31:02'</span> <span class="c1"># with ISO 8601</span>
</pre></div>
</div>
<p>And can be get in different ways too:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">str</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="o">--></span> <span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">30</span><span class="n">T17</span><span class="p">:</span><span class="mi">31</span><span class="p">:</span><span class="mi">00</span>
<span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span> <span class="o">--></span> <span class="n">datetime64</span><span class="p">(</span><span class="mi">1199164177</span><span class="p">,</span> <span class="s1">'s'</span><span class="p">)</span>
<span class="nb">str</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">item</span><span class="p">())</span> <span class="o">--></span> <span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">30</span> <span class="mi">17</span><span class="p">:</span><span class="mi">31</span><span class="p">:</span><span class="mi">00</span> <span class="c1"># datetime module object</span>
<span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">item</span><span class="p">())</span> <span class="o">--></span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="mi">2008</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">30</span><span class="p">,</span> <span class="mi">17</span><span class="p">,</span> <span class="mi">31</span><span class="p">)</span> <span class="c1"># idem</span>
<span class="nb">str</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="o">--></span> <span class="p">[</span><span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">30</span><span class="n">T17</span><span class="p">:</span><span class="mi">31</span><span class="p">:</span><span class="mi">00</span> <span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">30</span><span class="n">T17</span><span class="p">:</span><span class="mi">31</span><span class="p">:</span><span class="mi">01</span> <span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">30</span><span class="n">T17</span><span class="p">:</span><span class="mi">31</span><span class="p">:</span><span class="mi">02</span><span class="p">]</span>
<span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="o">--></span> <span class="n">array</span><span class="p">([</span><span class="mi">1199164176</span><span class="p">,</span> <span class="mi">1199164177</span><span class="p">,</span> <span class="mi">1199164178</span><span class="p">],</span>
<span class="n">dtype</span><span class="o">=</span><span class="s1">'datetime64[s]'</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="comparisons">
<h4>Comparisons<a class="headerlink" href="#comparisons" title="Link to this heading">#</a></h4>
<p>The comparisons will be supported too:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="s1">'1980'</span><span class="p">],</span> <span class="s1">'M8[Y]'</span><span class="p">)</span> <span class="o">==</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="s1">'1979'</span><span class="p">],</span> <span class="s1">'M8[Y]'</span><span class="p">)</span>
<span class="o">--></span> <span class="p">[</span><span class="kc">False</span><span class="p">]</span>
</pre></div>
</div>
<p>or by applying broadcasting:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="s1">'1979'</span><span class="p">,</span> <span class="s1">'1980'</span><span class="p">],</span> <span class="s1">'M8[Y]'</span><span class="p">)</span> <span class="o">==</span> <span class="n">numpy</span><span class="o">.</span><span class="n">datetime64</span><span class="p">(</span><span class="s1">'1980'</span><span class="p">,</span> <span class="s1">'Y'</span><span class="p">)</span>
<span class="o">--></span> <span class="p">[</span><span class="kc">False</span><span class="p">,</span> <span class="kc">True</span><span class="p">]</span>
</pre></div>
</div>
<p>The next should work too:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="s1">'1979'</span><span class="p">,</span> <span class="s1">'1980'</span><span class="p">],</span> <span class="s1">'M8[Y]'</span><span class="p">)</span> <span class="o">==</span> <span class="s1">'1980-01-01'</span>
<span class="o">--></span> <span class="p">[</span><span class="kc">False</span><span class="p">,</span> <span class="kc">True</span><span class="p">]</span>
</pre></div>
</div>
<p>because the right hand expression can be broadcasted into an array of 2
elements of dtype ‘M8[Y]’.</p>
</section>
<section id="compatibility-issues">
<h4>Compatibility issues<a class="headerlink" href="#compatibility-issues" title="Link to this heading">#</a></h4>
<p>This will be fully compatible with the <code class="docutils literal notranslate"><span class="pre">datetime</span></code> class of the
<code class="docutils literal notranslate"><span class="pre">datetime</span></code> module of Python only when using a time unit of
microseconds. For other time units, the conversion process will lose
precision or will overflow as needed. The conversion from/to a
<code class="docutils literal notranslate"><span class="pre">datetime</span></code> object doesn’t take leap seconds into account.</p>
</section>
</section>
<section id="timedelta64">
<h3><code class="docutils literal notranslate"><span class="pre">timedelta64</span></code><a class="headerlink" href="#timedelta64" title="Link to this heading">#</a></h3>
<p>It represents a time that is relative (i.e. not absolute). It is
implemented internally as an <code class="docutils literal notranslate"><span class="pre">int64</span></code> type.</p>
<p>In time unit <em>conversions</em> and time <em>representations</em> (but not in other
time computations), the value -2**63 (0x8000000000000000) is interpreted
as an invalid or unknown time, <em>Not a Time</em> or <em>NaT</em>. See the section
on time unit conversions for more information.</p>
<section id="id4">
<h4>Time units<a class="headerlink" href="#id4" title="Link to this heading">#</a></h4>
<p>It accepts different time units, each of them implying a different time
span. The table below describes the time units supported with their
corresponding time spans.</p>
<div class="pst-scrollable-table-container"><table class="table">
<thead>
<tr class="row-odd"><th class="head" colspan="2"><p>Time unit</p></th>
<th class="head"><p>Time span</p></th>
</tr>
<tr class="row-even"><th class="head"><p>Code</p></th>
<th class="head"><p>Meaning</p></th>
<th class="head"></th>
</tr>
</thead>
<tbody>
<tr class="row-odd"><td><p>Y</p></td>
<td><p>year</p></td>
<td><p>+- 9.2e18 years</p></td>
</tr>
<tr class="row-even"><td><p>M</p></td>
<td><p>month</p></td>
<td><p>+- 7.6e17 years</p></td>
</tr>
<tr class="row-odd"><td><p>W</p></td>
<td><p>week</p></td>
<td><p>+- 1.7e17 years</p></td>
</tr>
<tr class="row-even"><td><p>B</p></td>
<td><p>business day</p></td>
<td><p>+- 3.5e16 years</p></td>
</tr>
<tr class="row-odd"><td><p>D</p></td>
<td><p>day</p></td>
<td><p>+- 2.5e16 years</p></td>
</tr>
<tr class="row-even"><td><p>h</p></td>
<td><p>hour</p></td>
<td><p>+- 1.0e15 years</p></td>
</tr>
<tr class="row-odd"><td><p>m</p></td>
<td><p>minute</p></td>
<td><p>+- 1.7e13 years</p></td>
</tr>
<tr class="row-even"><td><p>s</p></td>
<td><p>second</p></td>
<td><p>+- 2.9e12 years</p></td>
</tr>
<tr class="row-odd"><td><p>ms</p></td>
<td><p>millisecond</p></td>
<td><p>+- 2.9e9 years</p></td>
</tr>
<tr class="row-even"><td><p>us</p></td>
<td><p>microsecond</p></td>
<td><p>+- 2.9e6 years</p></td>
</tr>
<tr class="row-odd"><td><p>c#</p></td>
<td><p>ticks (100ns)</p></td>
<td><p>+- 2.9e4 years</p></td>
</tr>
<tr class="row-even"><td><p>ns</p></td>
<td><p>nanosecond</p></td>
<td><p>+- 292 years</p></td>
</tr>
<tr class="row-odd"><td><p>ps</p></td>
<td><p>picosecond</p></td>
<td><p>+- 106 days</p></td>
</tr>
<tr class="row-even"><td><p>fs</p></td>
<td><p>femtosecond</p></td>
<td><p>+- 2.6 hours</p></td>
</tr>
<tr class="row-odd"><td><p>as</p></td>
<td><p>attosecond</p></td>
<td><p>+- 9.2 seconds</p></td>
</tr>
</tbody>
</table>
</div>
<p>The value of a time delta is thus <em>an integer number of units of the
chosen time unit</em>.</p>
</section>
<section id="building-a-timedelta64-dtype">
<h4>Building a <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code> dtype<a class="headerlink" href="#building-a-timedelta64-dtype" title="Link to this heading">#</a></h4>
<p>The proposed ways to specify the time unit in the dtype constructor are:</p>
<p>Using the long string notation:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">dtype</span><span class="p">(</span><span class="s1">'timedelta64[us]'</span><span class="p">)</span>
</pre></div>
</div>
<p>Using the short string notation:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">dtype</span><span class="p">(</span><span class="s1">'m8[us]'</span><span class="p">)</span>
</pre></div>
</div>
<p>The default is micro-seconds if no default is specified: ‘m8’ is equivalent to ‘m8[us]’</p>
</section>
<section id="id5">
<h4>Setting and getting values<a class="headerlink" href="#id5" title="Link to this heading">#</a></h4>
<p>The objects with this dtype can be set in a series of ways:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s1">'m8[ms]'</span><span class="p">)</span>
<span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">12</span> <span class="c1"># assign to 12 ms</span>
<span class="n">t</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">timedelta</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">13000</span><span class="p">)</span> <span class="c1"># 13 ms</span>
<span class="n">t</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'0:00:00.014'</span> <span class="c1"># 14 ms</span>
</pre></div>
</div>
<p>And can be get in different ways too:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">str</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span> <span class="o">--></span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.012</span>
<span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span> <span class="o">--></span> <span class="n">timedelta64</span><span class="p">(</span><span class="mi">13</span><span class="p">,</span> <span class="s1">'ms'</span><span class="p">)</span>
<span class="nb">str</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">item</span><span class="p">())</span> <span class="o">--></span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.012000</span> <span class="c1"># datetime module object</span>
<span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">item</span><span class="p">())</span> <span class="o">--></span> <span class="n">datetime</span><span class="o">.</span><span class="n">timedelta</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">12000</span><span class="p">)</span> <span class="c1"># idem</span>
<span class="nb">str</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="o">--></span> <span class="p">[</span><span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.012</span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.014</span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.014</span><span class="p">]</span>
<span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="o">--></span> <span class="n">array</span><span class="p">([</span><span class="mi">12</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">14</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"timedelta64[ms]"</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="id6">
<h4>Comparisons<a class="headerlink" href="#id6" title="Link to this heading">#</a></h4>
<p>The comparisons will be supported too:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">12</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">14</span><span class="p">],</span> <span class="s1">'m8[ms]'</span><span class="p">)</span> <span class="o">==</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">12</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">13</span><span class="p">],</span> <span class="s1">'m8[ms]'</span><span class="p">)</span>
<span class="o">--></span> <span class="p">[</span><span class="kc">True</span><span class="p">,</span> <span class="kc">True</span><span class="p">,</span> <span class="kc">False</span><span class="p">]</span>
</pre></div>
</div>
<p>or by applying broadcasting:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">12</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">14</span><span class="p">],</span> <span class="s1">'m8[ms]'</span><span class="p">)</span> <span class="o">==</span> <span class="n">numpy</span><span class="o">.</span><span class="n">timedelta64</span><span class="p">(</span><span class="mi">13</span><span class="p">,</span> <span class="s1">'ms'</span><span class="p">)</span>
<span class="o">--></span> <span class="p">[</span><span class="kc">False</span><span class="p">,</span> <span class="kc">True</span><span class="p">,</span> <span class="kc">False</span><span class="p">]</span>
</pre></div>
</div>
<p>The next should work too:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">12</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">14</span><span class="p">],</span> <span class="s1">'m8[ms]'</span><span class="p">)</span> <span class="o">==</span> <span class="s1">'0:00:00.012'</span>
<span class="o">--></span> <span class="p">[</span><span class="kc">True</span><span class="p">,</span> <span class="kc">False</span><span class="p">,</span> <span class="kc">False</span><span class="p">]</span>
</pre></div>
</div>
<p>because the right hand expression can be broadcasted into an array of 3
elements of dtype ‘m8[ms]’.</p>
</section>
<section id="id7">
<h4>Compatibility issues<a class="headerlink" href="#id7" title="Link to this heading">#</a></h4>
<p>This will be fully compatible with the <code class="docutils literal notranslate"><span class="pre">timedelta</span></code> class of the
<code class="docutils literal notranslate"><span class="pre">datetime</span></code> module of Python only when using a time unit of
microseconds. For other units, the conversion process will lose
precision or will overflow as needed.</p>
</section>
</section>
</section>
<section id="examples-of-use">
<h2>Examples of use<a class="headerlink" href="#examples-of-use" title="Link to this heading">#</a></h2>
<p>Here it is an example of use for the <code class="docutils literal notranslate"><span class="pre">datetime64</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">5</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">datetime64</span><span class="p">(</span><span class="mi">42</span><span class="p">,</span> <span class="s1">'us'</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">5</span><span class="p">]:</span> <span class="n">datetime64</span><span class="p">(</span><span class="mi">42</span><span class="p">,</span> <span class="s1">'us'</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">6</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">numpy</span><span class="o">.</span><span class="n">datetime64</span><span class="p">(</span><span class="mi">42</span><span class="p">,</span> <span class="s1">'us'</span><span class="p">)</span>
<span class="mi">1970</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">01</span><span class="n">T00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.000042</span> <span class="c1"># representation in ISO 8601 format</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">7</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">numpy</span><span class="o">.</span><span class="n">datetime64</span><span class="p">(</span><span class="mf">367.7</span><span class="p">,</span> <span class="s1">'D'</span><span class="p">)</span> <span class="c1"># decimal part is lost</span>
<span class="mi">1971</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">02</span> <span class="c1"># still ISO 8601 format</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">8</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="s1">'2008-07-18T12:23:18'</span><span class="p">,</span> <span class="s1">'m'</span><span class="p">)</span> <span class="c1"># from ISO 8601</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">8</span><span class="p">]:</span> <span class="n">datetime64</span><span class="p">(</span><span class="mi">20273063</span><span class="p">,</span> <span class="s1">'m'</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">9</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">numpy</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="s1">'2008-07-18T12:23:18'</span><span class="p">,</span> <span class="s1">'m'</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">9</span><span class="p">]:</span> <span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">18</span><span class="n">T12</span><span class="p">:</span><span class="mi">23</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">t</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"datetime64[ms]"</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="o">.</span><span class="n">now</span><span class="p">()</span> <span class="c1"># setter in action</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">12</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">t</span>
<span class="p">[</span><span class="mi">2008</span><span class="o">-</span><span class="mi">07</span><span class="o">-</span><span class="mi">16</span><span class="n">T13</span><span class="p">:</span><span class="mi">39</span><span class="p">:</span><span class="mf">25.315</span> <span class="mi">1970</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">01</span><span class="n">T00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.000</span>
<span class="mi">1970</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">01</span><span class="n">T00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.000</span> <span class="mi">1970</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">01</span><span class="n">T00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.000</span>
<span class="mi">1970</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">01</span><span class="n">T00</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.000</span><span class="p">]</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">13</span><span class="p">]:</span> <span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">13</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">267859210457</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"datetime64[ms]"</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">14</span><span class="p">]:</span> <span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">item</span><span class="p">()</span> <span class="c1"># getter in action</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">14</span><span class="p">]:</span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="p">(</span><span class="mi">2008</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">39</span><span class="p">,</span> <span class="mi">25</span><span class="p">,</span> <span class="mi">315000</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">15</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">t</span><span class="o">.</span><span class="n">dtype</span>
<span class="n">dtype</span><span class="p">(</span><span class="s1">'datetime64[ms]'</span><span class="p">)</span>
</pre></div>
</div>
<p>And here it goes an example of use for the <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">5</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">timedelta64</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="s1">'us'</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">5</span><span class="p">]:</span> <span class="n">timedelta64</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="s1">'us'</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">6</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">numpy</span><span class="o">.</span><span class="n">timedelta64</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="s1">'us'</span><span class="p">)</span>
<span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">00.000010</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">7</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">numpy</span><span class="o">.</span><span class="n">timedelta64</span><span class="p">(</span><span class="mf">3600.2</span><span class="p">,</span> <span class="s1">'m'</span><span class="p">)</span> <span class="c1"># decimal part is lost</span>
<span class="mi">2</span> <span class="n">days</span><span class="p">,</span> <span class="mi">12</span><span class="p">:</span><span class="mi">00</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">8</span><span class="p">]:</span> <span class="n">t1</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"datetime64[ms]"</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">9</span><span class="p">]:</span> <span class="n">t2</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"datetime64[ms]"</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">t</span> <span class="o">=</span> <span class="n">t2</span> <span class="o">-</span> <span class="n">t1</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">timedelta</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">24</span><span class="p">)</span> <span class="c1"># setter in action</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">12</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">t</span>
<span class="p">[</span><span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">24.000</span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">01.000</span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">01.000</span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">01.000</span> <span class="mi">0</span><span class="p">:</span><span class="mi">00</span><span class="p">:</span><span class="mf">01.000</span><span class="p">]</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">13</span><span class="p">]:</span> <span class="nb">print</span> <span class="nb">repr</span><span class="p">(</span><span class="n">t</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">13</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">24000</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"timedelta64[ms]"</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">14</span><span class="p">]:</span> <span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">item</span><span class="p">()</span> <span class="c1"># getter in action</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">14</span><span class="p">]:</span> <span class="n">datetime</span><span class="o">.</span><span class="n">timedelta</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">24</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">15</span><span class="p">]:</span> <span class="nb">print</span> <span class="n">t</span><span class="o">.</span><span class="n">dtype</span>
<span class="n">dtype</span><span class="p">(</span><span class="s1">'timedelta64[s]'</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="operating-with-date-time-arrays">
<h2>Operating with date/time arrays<a class="headerlink" href="#operating-with-date-time-arrays" title="Link to this heading">#</a></h2>
<section id="datetime64-vs-datetime64">
<h3><code class="docutils literal notranslate"><span class="pre">datetime64</span></code> vs <code class="docutils literal notranslate"><span class="pre">datetime64</span></code><a class="headerlink" href="#datetime64-vs-datetime64" title="Link to this heading">#</a></h3>
<p>The only arithmetic operation allowed between absolute dates is the
subtraction:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s2">"M8[s]"</span><span class="p">)</span> <span class="o">-</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s2">"M8[s]"</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="n">timedelta64</span><span class="p">[</span><span class="n">s</span><span class="p">])</span>
</pre></div>
</div>
<p>But not other operations:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s2">"M8[s]"</span><span class="p">)</span> <span class="o">+</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s2">"M8[s]"</span><span class="p">)</span>
<span class="ne">TypeError</span><span class="p">:</span> <span class="n">unsupported</span> <span class="n">operand</span> <span class="nb">type</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="k">for</span> <span class="o">+</span><span class="p">:</span> <span class="s1">'numpy.ndarray'</span> <span class="ow">and</span> <span class="s1">'numpy.ndarray'</span>
</pre></div>
</div>
<p>Comparisons between absolute dates are allowed.</p>
<section id="casting-rules">
<h4>Casting rules<a class="headerlink" href="#casting-rules" title="Link to this heading">#</a></h4>
<p>When operating (basically, only the subtraction will be allowed) two
absolute times with different unit times, the outcome would be to raise
an exception. This is because the ranges and time-spans of the different
time units can be very different, and it is not clear at all what time
unit will be preferred for the user. For example, this should be
allowed:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"M8[Y]"</span><span class="p">)</span> <span class="o">-</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"M8[Y]"</span><span class="p">)</span>
<span class="go">array([1, 1, 1], dtype="timedelta64[Y]")</span>
</pre></div>
</div>
<p>But the next should not:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"M8[Y]"</span><span class="p">)</span> <span class="o">-</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"M8[ns]"</span><span class="p">)</span>
<span class="go">raise numpy.IncompatibleUnitError # what unit to choose?</span>
</pre></div>
</div>
</section>
</section>
<section id="datetime64-vs-timedelta64">
<h3><code class="docutils literal notranslate"><span class="pre">datetime64</span></code> vs <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code><a class="headerlink" href="#datetime64-vs-timedelta64" title="Link to this heading">#</a></h3>
<p>It will be possible to add and subtract relative times from absolute
dates:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="s2">"M8[Y]"</span><span class="p">)</span> <span class="o">+</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="s2">"m8[Y]"</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">1971</span><span class="p">,</span> <span class="mi">1971</span><span class="p">,</span> <span class="mi">1971</span><span class="p">,</span> <span class="mi">1971</span><span class="p">,</span> <span class="mi">1971</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="n">datetime64</span><span class="p">[</span><span class="n">Y</span><span class="p">])</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="s2">"M8[Y]"</span><span class="p">)</span> <span class="o">-</span> <span class="mi">2</span> <span class="o">*</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="s2">"m8[Y]"</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">1969</span><span class="p">,</span> <span class="mi">1969</span><span class="p">,</span> <span class="mi">1969</span><span class="p">,</span> <span class="mi">1969</span><span class="p">,</span> <span class="mi">1969</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="n">datetime64</span><span class="p">[</span><span class="n">Y</span><span class="p">])</span>
</pre></div>
</div>
<p>But not other operations:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">12</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="s2">"M8[Y]"</span><span class="p">)</span> <span class="o">*</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="s2">"m8[Y]"</span><span class="p">)</span>
<span class="ne">TypeError</span><span class="p">:</span> <span class="n">unsupported</span> <span class="n">operand</span> <span class="nb">type</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="k">for</span> <span class="o">*</span><span class="p">:</span> <span class="s1">'numpy.ndarray'</span> <span class="ow">and</span> <span class="s1">'numpy.ndarray'</span>
</pre></div>
</div>
<section id="id8">
<h4>Casting rules<a class="headerlink" href="#id8" title="Link to this heading">#</a></h4>
<p>In this case the absolute time should have priority for determining the
time unit of the outcome. That would represent what the people wants to
do most of the times. For example, this would allow to do:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">series</span> <span class="o">=</span> <span class="n">numpy</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="s1">'1970-01-01'</span><span class="p">,</span> <span class="s1">'1970-02-01'</span><span class="p">,</span> <span class="s1">'1970-09-01'</span><span class="p">],</span>
<span class="go">dtype='datetime64[D]')</span>
<span class="gp">>>> </span><span class="n">series2</span> <span class="o">=</span> <span class="n">series</span> <span class="o">+</span> <span class="n">numpy</span><span class="o">.</span><span class="n">timedelta</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="s1">'Y'</span><span class="p">)</span> <span class="c1"># Add 2 relative years</span>
<span class="gp">>>> </span><span class="n">series2</span>
<span class="go">array(['1972-01-01', '1972-02-01', '1972-09-01'],</span>
<span class="go">dtype='datetime64[D]') # the 'D'ay time unit has been chosen</span>
</pre></div>
</div>
</section>
</section>
<section id="timedelta64-vs-timedelta64">
<h3><code class="docutils literal notranslate"><span class="pre">timedelta64</span></code> vs <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code><a class="headerlink" href="#timedelta64-vs-timedelta64" title="Link to this heading">#</a></h3>
<p>Finally, it will be possible to operate with relative times as if they
were regular int64 dtypes <em>as long as</em> the result can be converted back
into a <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s1">'m8[us]'</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"timedelta64[us]"</span><span class="p">)</span>
<span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="p">(</span><span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s1">'m8[M]'</span><span class="p">)</span> <span class="o">+</span> <span class="mi">2</span><span class="p">)</span> <span class="o">**</span> <span class="mi">3</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">27</span><span class="p">,</span> <span class="mi">27</span><span class="p">,</span> <span class="mi">27</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"timedelta64[M]"</span><span class="p">)</span>
</pre></div>
</div>
<p>But:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>In [12]: numpy.ones(5, 'm8') + 1j
TypeError: the result cannot be converted into a ``timedelta64``
</pre></div>
</div>
<section id="id9">
<h4>Casting rules<a class="headerlink" href="#id9" title="Link to this heading">#</a></h4>
<p>When combining two <code class="docutils literal notranslate"><span class="pre">timedelta64</span></code> dtypes with different time units the
outcome will be the shorter of both (“keep the precision” rule). For
example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s1">'m8[s]'</span><span class="p">)</span> <span class="o">+</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s1">'m8[m]'</span><span class="p">)</span>
<span class="n">Out</span><span class="p">[</span><span class="mi">10</span><span class="p">]:</span> <span class="n">array</span><span class="p">([</span><span class="mi">61</span><span class="p">,</span> <span class="mi">61</span><span class="p">,</span> <span class="mi">61</span><span class="p">],</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">"timedelta64[s]"</span><span class="p">)</span>
</pre></div>
</div>
<p>However, due to the impossibility to know the exact duration of a
relative year or a relative month, when these time units appear in one
of the operands, the operation will not be allowed:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">In</span> <span class="p">[</span><span class="mi">11</span><span class="p">]:</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s1">'m8[Y]'</span><span class="p">)</span> <span class="o">+</span> <span class="n">numpy</span><span class="o">.</span><span class="n">ones</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="s1">'m8[D]'</span><span class="p">)</span>
<span class="k">raise</span> <span class="n">numpy</span><span class="o">.</span><span class="n">IncompatibleUnitError</span> <span class="c1"># how to convert relative years to days?</span>
</pre></div>
</div>
<p>In order to being able to perform the above operation a new NumPy
function, called <code class="docutils literal notranslate"><span class="pre">change_timeunit</span></code> is proposed. Its signature will