-
Notifications
You must be signed in to change notification settings - Fork 54
/
Copy pathMatplotlib.html
7116 lines (5882 loc) · 676 KB
/
Matplotlib.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 class="writer-html5" lang="en" >
<head>
<meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" />
<meta content="Topic: Plotting with matplotlib, Difficulty: Easy, Category: Section" name="description" />
<meta content="plot, matplotlib, figure, axes, functional, object oriented, histogram, image, save, load, color, colormap, API, style, notebook, inline" name="keywords" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Matplotlib — Python Like You Mean It</title>
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
<link rel="stylesheet" href="../_static/css/theme.css" type="text/css" />
<link rel="stylesheet" href="../_static/my_theme.css" type="text/css" />
<!--[if lt IE 9]>
<script src="../_static/js/html5shiv.min.js"></script>
<![endif]-->
<script data-url_root="../" id="documentation_options" src="../_static/documentation_options.js"></script>
<script src="../_static/jquery.js"></script>
<script src="../_static/underscore.js"></script>
<script src="../_static/doctools.js"></script>
<script async="async" src="https://www.googletagmanager.com/gtag/js?id=UA-115029372-1"></script>
<script src="../_static/gtag.js"></script>
<script crossorigin="anonymous" integrity="sha256-Ae2Vz/4ePdIu6ZyI/5ZGsYnb+m0JlOmKPjt6XZ9JJkA=" src="https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js"></script>
<script>window.MathJax = {"tex": {"inlineMath": [["$", "$"], ["\\(", "\\)"]], "processEscapes": true}, "options": {"ignoreHtmlClass": "tex2jax_ignore|mathjax_ignore|document", "processHtmlClass": "tex2jax_process|mathjax_process|math|output_area"}}</script>
<script defer="defer" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script>
<script src="../_static/js/theme.js"></script>
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="next" title="Working with Files" href="WorkingWithFiles.html" />
<link rel="prev" title="Writing Good Code" href="Writing_Good_Code.html" />
</head>
<body class="wy-body-for-nav">
<div class="wy-grid-for-nav">
<nav data-toggle="wy-nav-shift" class="wy-nav-side">
<div class="wy-side-scroll">
<div class="wy-side-nav-search" >
<a href="../index.html" class="icon icon-home"> Python Like You Mean It
</a>
<div class="version">
1.4
</div>
<div role="search">
<form id="rtd-search-form" class="wy-form" action="../search.html" method="get">
<input type="text" name="q" placeholder="Search docs" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
</div><div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="Navigation menu">
<p class="caption" role="heading"><span class="caption-text">Table of Contents:</span></p>
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="../intro.html">Python Like You Mean It</a></li>
<li class="toctree-l1"><a class="reference internal" href="../module_1.html">Module 1: Getting Started with Python</a></li>
<li class="toctree-l1"><a class="reference internal" href="../module_2.html">Module 2: The Essentials of Python</a></li>
<li class="toctree-l1"><a class="reference internal" href="../module_2_problems.html">Module 2: Problems</a></li>
<li class="toctree-l1"><a class="reference internal" href="../module_3.html">Module 3: The Essentials of NumPy</a></li>
<li class="toctree-l1"><a class="reference internal" href="../module_3_problems.html">Module 3: Problems</a></li>
<li class="toctree-l1"><a class="reference internal" href="../module_4.html">Module 4: Object Oriented Programming</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="../module_5.html">Module 5: Odds and Ends</a><ul class="current">
<li class="toctree-l2"><a class="reference internal" href="Writing_Good_Code.html">Writing Good Code</a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#">Matplotlib</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#Plotting-in-Jupyter-Notebooks">Plotting in Jupyter Notebooks</a></li>
<li class="toctree-l3"><a class="reference internal" href="#Creating-Figures-and-Axes-with-pyplot.subplots">Creating Figures and Axes with <code class="docutils literal notranslate"><span class="pre">pyplot.subplots</span></code></a><ul>
<li class="toctree-l4"><a class="reference internal" href="#Plotting-and-Saving-a-Figure">Plotting and Saving a Figure</a></li>
<li class="toctree-l4"><a class="reference internal" href="#The-Axes-Object">The Axes Object</a></li>
<li class="toctree-l4"><a class="reference internal" href="#The-Figure-Object-(Saving-Figures)">The Figure Object (Saving Figures)</a></li>
</ul>
</li>
<li class="toctree-l3"><a class="reference internal" href="#Displaying-Images">Displaying Images</a></li>
<li class="toctree-l3"><a class="reference internal" href="#Beyond-Matplotlib">Beyond Matplotlib</a></li>
<li class="toctree-l3"><a class="reference internal" href="#Links-to-Official-Documentation">Links to Official Documentation</a></li>
<li class="toctree-l3"><a class="reference internal" href="#Reading-Comprehension-Exercise-Solutions:">Reading Comprehension Exercise Solutions:</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="WorkingWithFiles.html">Working with Files</a></li>
<li class="toctree-l2"><a class="reference internal" href="Modules_and_Packages.html">Import: Modules and Packages</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../changes.html">Changelog</a></li>
</ul>
</div>
</div>
</nav>
<section data-toggle="wy-nav-shift" class="wy-nav-content-wrap"><nav class="wy-nav-top" aria-label="Mobile navigation menu" >
<i data-toggle="wy-nav-top" class="fa fa-bars"></i>
<a href="../index.html">Python Like You Mean It</a>
</nav>
<div class="wy-nav-content">
<div class="rst-content">
<div role="navigation" aria-label="Page navigation">
<ul class="wy-breadcrumbs">
<li><a href="../index.html" class="icon icon-home"></a> »</li>
<li><a href="../module_5.html">Module 5: Odds and Ends</a> »</li>
<li>Matplotlib</li>
<li class="wy-breadcrumbs-aside">
<a href="../_sources/Module5_OddsAndEnds/Matplotlib.ipynb.txt" rel="nofollow"> View page source</a>
</li>
</ul>
<hr/>
</div>
<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
<div itemprop="articleBody">
<style>
/* CSS for nbsphinx extension */
/* remove conflicting styling from Sphinx themes */
div.nbinput.container div.prompt *,
div.nboutput.container div.prompt *,
div.nbinput.container div.input_area pre,
div.nboutput.container div.output_area pre,
div.nbinput.container div.input_area .highlight,
div.nboutput.container div.output_area .highlight {
border: none;
padding: 0;
margin: 0;
box-shadow: none;
}
div.nbinput.container > div[class*=highlight],
div.nboutput.container > div[class*=highlight] {
margin: 0;
}
div.nbinput.container div.prompt *,
div.nboutput.container div.prompt * {
background: none;
}
div.nboutput.container div.output_area .highlight,
div.nboutput.container div.output_area pre {
background: unset;
}
div.nboutput.container div.output_area div.highlight {
color: unset; /* override Pygments text color */
}
/* avoid gaps between output lines */
div.nboutput.container div[class*=highlight] pre {
line-height: normal;
}
/* input/output containers */
div.nbinput.container,
div.nboutput.container {
display: -webkit-flex;
display: flex;
align-items: flex-start;
margin: 0;
width: 100%;
}
@media (max-width: 540px) {
div.nbinput.container,
div.nboutput.container {
flex-direction: column;
}
}
/* input container */
div.nbinput.container {
padding-top: 5px;
}
/* last container */
div.nblast.container {
padding-bottom: 5px;
}
/* input prompt */
div.nbinput.container div.prompt pre {
color: #307FC1;
}
/* output prompt */
div.nboutput.container div.prompt pre {
color: #BF5B3D;
}
/* all prompts */
div.nbinput.container div.prompt,
div.nboutput.container div.prompt {
width: 4.5ex;
padding-top: 5px;
position: relative;
user-select: none;
}
div.nbinput.container div.prompt > div,
div.nboutput.container div.prompt > div {
position: absolute;
right: 0;
margin-right: 0.3ex;
}
@media (max-width: 540px) {
div.nbinput.container div.prompt,
div.nboutput.container div.prompt {
width: unset;
text-align: left;
padding: 0.4em;
}
div.nboutput.container div.prompt.empty {
padding: 0;
}
div.nbinput.container div.prompt > div,
div.nboutput.container div.prompt > div {
position: unset;
}
}
/* disable scrollbars on prompts */
div.nbinput.container div.prompt pre,
div.nboutput.container div.prompt pre {
overflow: hidden;
}
/* input/output area */
div.nbinput.container div.input_area,
div.nboutput.container div.output_area {
-webkit-flex: 1;
flex: 1;
overflow: auto;
}
@media (max-width: 540px) {
div.nbinput.container div.input_area,
div.nboutput.container div.output_area {
width: 100%;
}
}
/* input area */
div.nbinput.container div.input_area {
border: 1px solid #e0e0e0;
border-radius: 2px;
/*background: #f5f5f5;*/
}
/* override MathJax center alignment in output cells */
div.nboutput.container div[class*=MathJax] {
text-align: left !important;
}
/* override sphinx.ext.imgmath center alignment in output cells */
div.nboutput.container div.math p {
text-align: left;
}
/* standard error */
div.nboutput.container div.output_area.stderr {
background: #fdd;
}
/* ANSI colors */
.ansi-black-fg { color: #3E424D; }
.ansi-black-bg { background-color: #3E424D; }
.ansi-black-intense-fg { color: #282C36; }
.ansi-black-intense-bg { background-color: #282C36; }
.ansi-red-fg { color: #E75C58; }
.ansi-red-bg { background-color: #E75C58; }
.ansi-red-intense-fg { color: #B22B31; }
.ansi-red-intense-bg { background-color: #B22B31; }
.ansi-green-fg { color: #00A250; }
.ansi-green-bg { background-color: #00A250; }
.ansi-green-intense-fg { color: #007427; }
.ansi-green-intense-bg { background-color: #007427; }
.ansi-yellow-fg { color: #DDB62B; }
.ansi-yellow-bg { background-color: #DDB62B; }
.ansi-yellow-intense-fg { color: #B27D12; }
.ansi-yellow-intense-bg { background-color: #B27D12; }
.ansi-blue-fg { color: #208FFB; }
.ansi-blue-bg { background-color: #208FFB; }
.ansi-blue-intense-fg { color: #0065CA; }
.ansi-blue-intense-bg { background-color: #0065CA; }
.ansi-magenta-fg { color: #D160C4; }
.ansi-magenta-bg { background-color: #D160C4; }
.ansi-magenta-intense-fg { color: #A03196; }
.ansi-magenta-intense-bg { background-color: #A03196; }
.ansi-cyan-fg { color: #60C6C8; }
.ansi-cyan-bg { background-color: #60C6C8; }
.ansi-cyan-intense-fg { color: #258F8F; }
.ansi-cyan-intense-bg { background-color: #258F8F; }
.ansi-white-fg { color: #C5C1B4; }
.ansi-white-bg { background-color: #C5C1B4; }
.ansi-white-intense-fg { color: #A1A6B2; }
.ansi-white-intense-bg { background-color: #A1A6B2; }
.ansi-default-inverse-fg { color: #FFFFFF; }
.ansi-default-inverse-bg { background-color: #000000; }
.ansi-bold { font-weight: bold; }
.ansi-underline { text-decoration: underline; }
div.nbinput.container div.input_area div[class*=highlight] > pre,
div.nboutput.container div.output_area div[class*=highlight] > pre,
div.nboutput.container div.output_area div[class*=highlight].math,
div.nboutput.container div.output_area.rendered_html,
div.nboutput.container div.output_area > div.output_javascript,
div.nboutput.container div.output_area:not(.rendered_html) > img{
padding: 5px;
margin: 0;
}
/* fix copybtn overflow problem in chromium (needed for 'sphinx_copybutton') */
div.nbinput.container div.input_area > div[class^='highlight'],
div.nboutput.container div.output_area > div[class^='highlight']{
overflow-y: hidden;
}
/* hide copybtn icon on prompts (needed for 'sphinx_copybutton') */
.prompt .copybtn {
display: none;
}
/* Some additional styling taken form the Jupyter notebook CSS */
div.rendered_html table {
border: none;
border-collapse: collapse;
border-spacing: 0;
color: black;
font-size: 12px;
table-layout: fixed;
}
div.rendered_html thead {
border-bottom: 1px solid black;
vertical-align: bottom;
}
div.rendered_html tr,
div.rendered_html th,
div.rendered_html td {
text-align: right;
vertical-align: middle;
padding: 0.5em 0.5em;
line-height: normal;
white-space: normal;
max-width: none;
border: none;
}
div.rendered_html th {
font-weight: bold;
}
div.rendered_html tbody tr:nth-child(odd) {
background: #f5f5f5;
}
div.rendered_html tbody tr:hover {
background: rgba(66, 165, 245, 0.2);
}
/* CSS overrides for sphinx_rtd_theme */
/* 24px margin */
.nbinput.nblast.container,
.nboutput.nblast.container {
margin-bottom: 19px; /* padding has already 5px */
}
/* ... except between code cells! */
.nblast.container + .nbinput.container {
margin-top: -19px;
}
.admonition > p:before {
margin-right: 4px; /* make room for the exclamation icon */
}
/* Fix math alignment, see https://github.com/rtfd/sphinx_rtd_theme/pull/686 */
.math {
text-align: unset;
}
</style>
<section id="Matplotlib">
<h1>Matplotlib<a class="headerlink" href="#Matplotlib" title="Permalink to this headline"></a></h1>
<p>In this section, we will introduce Matplotlib, the most long-lived Python package for plotting data and images. It is designed to work nicely with NumPy arrays, and natively uses two and three-dimensional arrays to represent images, (gray-scale and RGB, respectively). This section will introduce the basics of plotting and key features of Matplotlib.</p>
<p>There are many tutorials, “cheat sheets”, and other resources for using Matplotlib. Our goal here is to provide a treatment of Matplotlib with slightly deeper aims than simply showing you how to make “a plot that looks like …”. Specifically, our aim is to introduce Matplotib’s <a class="reference external" href="https://matplotlib.org/api/pyplot_summary.html#the-object-oriented-api">object oriented API</a>, instead of its <a class="reference external" href="https://matplotlib.org/api/pyplot_summary.html#the-pyplot-api">function-based API</a>. Let’s briefly draw a
distinction between these two APIs:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">matplotlib.pyplot</span> <span class="k">as</span> <span class="nn">plt</span>
<span class="c1"># prepare 50 x-coordinates and 50 y-coordinates</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">linspace</span><span class="p">(</span><span class="o">-</span><span class="n">np</span><span class="o">.</span><span class="n">pi</span><span class="p">,</span> <span class="n">np</span><span class="o">.</span><span class="n">pi</span><span class="p">,</span> <span class="mi">50</span><span class="p">)</span>
<span class="n">y</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">sin</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="c1"># Plot using matplotlib's object-oriented API:</span>
<span class="c1"># we figure and axis object: `fig` and `ax`</span>
<span class="n">fig</span><span class="p">,</span> <span class="n">ax</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">subplots</span><span class="p">()</span>
<span class="c1"># we then use these objects to draw-on and manipulate our plot</span>
<span class="n">ax</span><span class="o">.</span><span class="n">plot</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">)</span>
<span class="c1"># Plot using matplotlib's functional API:</span>
<span class="c1"># a single function call produces a plot; convenient but less flexible</span>
<span class="n">plt</span><span class="o">.</span><span class="n">plot</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">)</span>
</pre></div>
</div>
<p>Although the code that invokes the functional API is simpler, it is far less powerful and flexible than the object-oriented API, which produces figure (<code class="docutils literal notranslate"><span class="pre">fig</span></code>) and axes (<code class="docutils literal notranslate"><span class="pre">ax</span></code>) objects that we can leverage to customize our plot. You will likely see tutorials utilize the functional API in their examples, so it is useful to understand the distinction here. Shortly, you will learn how to leverage Matplotlib’s object-oriented API in powerful ways.</p>
<p>Consult the <a class="reference external" href="https://matplotlib.org/users/index.html">Matplotlib user’s guide</a>, as well as their <a class="reference external" href="https://matplotlib.org/tutorials/index.html">tutorials</a> for additional information about this plotting library.</p>
<p>Matplotlib is included in the Anaconda distribution of Python packages. The <code class="docutils literal notranslate"><span class="pre">pyplot</span></code> submodule of Matplotlib contains all of the essential plotting functionality, thus we will always need to import <code class="docutils literal notranslate"><span class="pre">pyplot</span></code>. It is standard to utilize the abbreviation “plt” when importing the <code class="docutils literal notranslate"><span class="pre">pyplot</span></code> submodule from Matplotlib:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># import matplotlib's pyplot submodule</span>
<span class="kn">import</span> <span class="nn">matplotlib.pyplot</span> <span class="k">as</span> <span class="nn">plt</span>
</pre></div>
</div>
<p>There are many tutorials and examples available online, which demonstrate Matplotlib’s wide range of capabilities for visualizing data. Here, we will only distill the essentials needed for understanding how to use Matplotlib effectively for typical data science applications.</p>
<section id="Plotting-in-Jupyter-Notebooks">
<h2>Plotting in Jupyter Notebooks<a class="headerlink" href="#Plotting-in-Jupyter-Notebooks" title="Permalink to this headline"></a></h2>
<p>While Matplotlib provides a graphical interface for plots so that we can plot data from the Python shell or IPython, the Jupyter notebook is the ideal environment for creating and refining data visualizations. The command <code class="docutils literal notranslate"><span class="pre">%matplotlib</span> <span class="pre">notebook</span></code>, when executed in a notebook, will instruct Matplotlib to embed its plots within that notebook, rather than opening a separate window for each plot.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># instructs Jupyter to embed plots within a notebook</span>
<span class="o">%</span><span class="n">matplotlib</span> <span class="n">notebook</span>
</pre></div>
</div>
<p>It need only be executed once in a given notebook to instruct plots to be embedded within that notebook. This will also allow us to interact with the plots that render within the notebook, enabling panning, zooming, and saving. We will proceed with this section with the assumption that we are embedding our plots in a notebook.</p>
<p>Finally, note that <code class="docutils literal notranslate"><span class="pre">%matplotlib</span> <span class="pre">notebook</span></code> is not a valid line of Python code, rather it is an example of a <a class="reference external" href="http://ipython.readthedocs.io/en/stable/interactive/magics.html">“magic command”</a> which is reserved to affect the behavior of the IPython console and Jupyter notebook.</p>
</section>
<section id="Creating-Figures-and-Axes-with-pyplot.subplots">
<h2>Creating Figures and Axes with <code class="docutils literal notranslate"><span class="pre">pyplot.subplots</span></code><a class="headerlink" href="#Creating-Figures-and-Axes-with-pyplot.subplots" title="Permalink to this headline"></a></h2>
<p>There are many different ways to create blank figure and axes objects in Matplotlib. Here, we will introduce the function <code class="docutils literal notranslate"><span class="pre">pyplot.subplots</span></code>, which creates a figure that contains axes on which data is plotted. We will see that the keyword argument <code class="docutils literal notranslate"><span class="pre">figsize</span></code> can be used to control the size of the figure, and that the keyword arguments <code class="docutils literal notranslate"><span class="pre">ncols</span></code> and <code class="docutils literal notranslate"><span class="pre">nrows</span></code> can be used to specify the grid on which the axes will be laid out within the figure.</p>
<p>In Matplotlib, the <code class="docutils literal notranslate"><span class="pre">Figure</span></code> object is used to contain one or more sets of <code class="docutils literal notranslate"><span class="pre">Axes</span></code> objects. Data is plotted within a given set of axes. The <code class="docutils literal notranslate"><span class="pre">subplots</span></code> function can be used to create a figure along with a specified layout of axes. By default, <code class="docutils literal notranslate"><span class="pre">subplots</span></code> will create a figure with a single set of axes; calling it will return the figure object and its axes object in a tuple:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">matplotlib.pyplot</span> <span class="k">as</span> <span class="nn">plt</span>
<span class="o">%</span><span class="n">matplotlib</span> <span class="n">notebook</span>
<span class="c1"># Creating a figure that contains a single</span>
<span class="c1"># set of axes. `plt.subplots()` returns</span>
<span class="c1"># the tuple: (Figure-instance, Axes-instance)</span>
<span class="n">fig</span><span class="p">,</span> <span class="n">ax</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">subplots</span><span class="p">()</span>
</pre></div>
</div>
<p>Executing this code will open a figure with a blank set of axes. We can use the <code class="docutils literal notranslate"><span class="pre">Axes</span></code> instance, <code class="docutils literal notranslate"><span class="pre">ax</span></code>, to plot data, add labels and a title to the plot, and add grid lines. The <code class="docutils literal notranslate"><span class="pre">Figure</span></code> instance, <code class="docutils literal notranslate"><span class="pre">fig</span></code>, controls higher-level features of the figure, such as the layout of the axes, the alignment of labels, and other factors. <code class="docutils literal notranslate"><span class="pre">fig</span></code> is perhaps most used for saving figures. Let’s plot a single period of a sine wave and then save it.</p>
<section id="Plotting-and-Saving-a-Figure">
<h3>Plotting and Saving a Figure<a class="headerlink" href="#Plotting-and-Saving-a-Figure" title="Permalink to this headline"></a></h3>
<div class="nbinput docutils container">
<div class="prompt highlight-none notranslate"><div class="highlight"><pre><span></span>[2]:
</pre></div>
</div>
<div class="input_area highlight-ipython3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># using subplots to create a figure with a singe set of axes</span>
<span class="c1"># plotting points on a sine curve</span>
<span class="kn">import</span> <span class="nn">numpy</span> <span class="k">as</span> <span class="nn">np</span>
<span class="kn">import</span> <span class="nn">matplotlib.pyplot</span> <span class="k">as</span> <span class="nn">plt</span>
<span class="o">%</span><span class="k">matplotlib</span> notebook
<span class="c1"># create a figure and set of axes</span>
<span class="n">fig</span><span class="p">,</span> <span class="n">ax</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">subplots</span><span class="p">()</span>
<span class="c1"># prepare 50 x-coordinates and 50 y-coordinates</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">linspace</span><span class="p">(</span><span class="o">-</span><span class="n">np</span><span class="o">.</span><span class="n">pi</span><span class="p">,</span> <span class="n">np</span><span class="o">.</span><span class="n">pi</span><span class="p">,</span> <span class="mi">50</span><span class="p">)</span>
<span class="n">y</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">sin</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="c1"># Plot data on the axes object.</span>
<span class="c1"># Plots corresponding x-y coordinate pairs,</span>
<span class="c1"># specified by the x-coordinates in `x`</span>
<span class="c1"># and the y-coordinates in `y`</span>
<span class="n">ax</span><span class="o">.</span><span class="n">plot</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">)</span>
<span class="c1"># the `fig` object is responsible for saving the</span>
<span class="c1"># full figure and all of its axes. Thefollowing</span>
<span class="c1"># command will save a png-image of this plot</span>
<span class="c1"># to the directory from where this code is executed.</span>
<span class="n">fig</span><span class="o">.</span><span class="n">savefig</span><span class="p">(</span><span class="s2">"sinewave_plt.png"</span><span class="p">);</span> <span class="c1"># the semicolon merely suppresses output to the console</span>
</pre></div>
</div>
</div>
<div class="nboutput docutils container">
<div class="prompt empty docutils container">
</div>
<div class="output_area docutils container">
<div class="output_javascript"></div>
<script type="text/javascript">
var element = document.currentScript.previousSibling.previousSibling;
/* Put everything inside the global mpl namespace */
window.mpl = {};
mpl.get_websocket_type = function() {
if (typeof(WebSocket) !== 'undefined') {
return WebSocket;
} else if (typeof(MozWebSocket) !== 'undefined') {
return MozWebSocket;
} else {
alert('Your browser does not have WebSocket support.' +
'Please try Chrome, Safari or Firefox ≥ 6. ' +
'Firefox 4 and 5 are also supported but you ' +
'have to enable WebSockets in about:config.');
};
}
mpl.figure = function(figure_id, websocket, ondownload, parent_element) {
this.id = figure_id;
this.ws = websocket;
this.supports_binary = (this.ws.binaryType != undefined);
if (!this.supports_binary) {
var warnings = document.getElementById("mpl-warnings");
if (warnings) {
warnings.style.display = 'block';
warnings.textContent = (
"This browser does not support binary websocket messages. " +
"Performance may be slow.");
}
}
this.imageObj = new Image();
this.context = undefined;
this.message = undefined;
this.canvas = undefined;
this.rubberband_canvas = undefined;
this.rubberband_context = undefined;
this.format_dropdown = undefined;
this.image_mode = 'full';
this.root = $('<div/>');
this._root_extra_style(this.root)
this.root.attr('style', 'display: inline-block');
$(parent_element).append(this.root);
this._init_header(this);
this._init_canvas(this);
this._init_toolbar(this);
var fig = this;
this.waiting = false;
this.ws.onopen = function () {
fig.send_message("supports_binary", {value: fig.supports_binary});
fig.send_message("send_image_mode", {});
if (mpl.ratio != 1) {
fig.send_message("set_dpi_ratio", {'dpi_ratio': mpl.ratio});
}
fig.send_message("refresh", {});
}
this.imageObj.onload = function() {
if (fig.image_mode == 'full') {
// Full images could contain transparency (where diff images
// almost always do), so we need to clear the canvas so that
// there is no ghosting.
fig.context.clearRect(0, 0, fig.canvas.width, fig.canvas.height);
}
fig.context.drawImage(fig.imageObj, 0, 0);
};
this.imageObj.onunload = function() {
fig.ws.close();
}
this.ws.onmessage = this._make_on_message_function(this);
this.ondownload = ondownload;
}
mpl.figure.prototype._init_header = function() {
var titlebar = $(
'<div class="ui-dialog-titlebar ui-widget-header ui-corner-all ' +
'ui-helper-clearfix"/>');
var titletext = $(
'<div class="ui-dialog-title" style="width: 100%; ' +
'text-align: center; padding: 3px;"/>');
titlebar.append(titletext)
this.root.append(titlebar);
this.header = titletext[0];
}
mpl.figure.prototype._canvas_extra_style = function(canvas_div) {
}
mpl.figure.prototype._root_extra_style = function(canvas_div) {
}
mpl.figure.prototype._init_canvas = function() {
var fig = this;
var canvas_div = $('<div/>');
canvas_div.attr('style', 'position: relative; clear: both; outline: 0');
function canvas_keyboard_event(event) {
return fig.key_event(event, event['data']);
}
canvas_div.keydown('key_press', canvas_keyboard_event);
canvas_div.keyup('key_release', canvas_keyboard_event);
this.canvas_div = canvas_div
this._canvas_extra_style(canvas_div)
this.root.append(canvas_div);
var canvas = $('<canvas/>');
canvas.addClass('mpl-canvas');
canvas.attr('style', "left: 0; top: 0; z-index: 0; outline: 0")
this.canvas = canvas[0];
this.context = canvas[0].getContext("2d");
var backingStore = this.context.backingStorePixelRatio ||
this.context.webkitBackingStorePixelRatio ||
this.context.mozBackingStorePixelRatio ||
this.context.msBackingStorePixelRatio ||
this.context.oBackingStorePixelRatio ||
this.context.backingStorePixelRatio || 1;
mpl.ratio = (window.devicePixelRatio || 1) / backingStore;
var rubberband = $('<canvas/>');
rubberband.attr('style', "position: absolute; left: 0; top: 0; z-index: 1;")
var pass_mouse_events = true;
canvas_div.resizable({
start: function(event, ui) {
pass_mouse_events = false;
},
resize: function(event, ui) {
fig.request_resize(ui.size.width, ui.size.height);
},
stop: function(event, ui) {
pass_mouse_events = true;
fig.request_resize(ui.size.width, ui.size.height);
},
});
function mouse_event_fn(event) {
if (pass_mouse_events)
return fig.mouse_event(event, event['data']);
}
rubberband.mousedown('button_press', mouse_event_fn);
rubberband.mouseup('button_release', mouse_event_fn);
// Throttle sequential mouse events to 1 every 20ms.
rubberband.mousemove('motion_notify', mouse_event_fn);
rubberband.mouseenter('figure_enter', mouse_event_fn);
rubberband.mouseleave('figure_leave', mouse_event_fn);
canvas_div.on("wheel", function (event) {
event = event.originalEvent;
event['data'] = 'scroll'
if (event.deltaY < 0) {
event.step = 1;
} else {
event.step = -1;
}
mouse_event_fn(event);
});
canvas_div.append(canvas);
canvas_div.append(rubberband);
this.rubberband = rubberband;
this.rubberband_canvas = rubberband[0];
this.rubberband_context = rubberband[0].getContext("2d");
this.rubberband_context.strokeStyle = "#000000";
this._resize_canvas = function(width, height) {
// Keep the size of the canvas, canvas container, and rubber band
// canvas in synch.
canvas_div.css('width', width)
canvas_div.css('height', height)
canvas.attr('width', width * mpl.ratio);
canvas.attr('height', height * mpl.ratio);
canvas.attr('style', 'width: ' + width + 'px; height: ' + height + 'px;');
rubberband.attr('width', width);
rubberband.attr('height', height);
}
// Set the figure to an initial 600x600px, this will subsequently be updated
// upon first draw.
this._resize_canvas(600, 600);
// Disable right mouse context menu.
$(this.rubberband_canvas).bind("contextmenu",function(e){
return false;
});
function set_focus () {
canvas.focus();
canvas_div.focus();
}
window.setTimeout(set_focus, 100);
}
mpl.figure.prototype._init_toolbar = function() {
var fig = this;
var nav_element = $('<div/>')
nav_element.attr('style', 'width: 100%');
this.root.append(nav_element);
// Define a callback function for later on.
function toolbar_event(event) {
return fig.toolbar_button_onclick(event['data']);
}
function toolbar_mouse_event(event) {
return fig.toolbar_button_onmouseover(event['data']);
}
for(var toolbar_ind in mpl.toolbar_items) {
var name = mpl.toolbar_items[toolbar_ind][0];
var tooltip = mpl.toolbar_items[toolbar_ind][1];
var image = mpl.toolbar_items[toolbar_ind][2];
var method_name = mpl.toolbar_items[toolbar_ind][3];
if (!name) {
// put a spacer in here.
continue;
}
var button = $('<button/>');
button.addClass('ui-button ui-widget ui-state-default ui-corner-all ' +
'ui-button-icon-only');
button.attr('role', 'button');
button.attr('aria-disabled', 'false');
button.click(method_name, toolbar_event);
button.mouseover(tooltip, toolbar_mouse_event);
var icon_img = $('<span/>');
icon_img.addClass('ui-button-icon-primary ui-icon');
icon_img.addClass(image);
icon_img.addClass('ui-corner-all');
var tooltip_span = $('<span/>');
tooltip_span.addClass('ui-button-text');
tooltip_span.html(tooltip);
button.append(icon_img);
button.append(tooltip_span);
nav_element.append(button);
}
var fmt_picker_span = $('<span/>');
var fmt_picker = $('<select/>');
fmt_picker.addClass('mpl-toolbar-option ui-widget ui-widget-content');
fmt_picker_span.append(fmt_picker);
nav_element.append(fmt_picker_span);
this.format_dropdown = fmt_picker[0];
for (var ind in mpl.extensions) {
var fmt = mpl.extensions[ind];
var option = $(
'<option/>', {selected: fmt === mpl.default_extension}).html(fmt);
fmt_picker.append(option)
}
// Add hover states to the ui-buttons
$( ".ui-button" ).hover(
function() { $(this).addClass("ui-state-hover");},
function() { $(this).removeClass("ui-state-hover");}
);
var status_bar = $('<span class="mpl-message"/>');
nav_element.append(status_bar);
this.message = status_bar[0];
}
mpl.figure.prototype.request_resize = function(x_pixels, y_pixels) {
// Request matplotlib to resize the figure. Matplotlib will then trigger a resize in the client,
// which will in turn request a refresh of the image.
this.send_message('resize', {'width': x_pixels, 'height': y_pixels});
}
mpl.figure.prototype.send_message = function(type, properties) {
properties['type'] = type;
properties['figure_id'] = this.id;
this.ws.send(JSON.stringify(properties));
}
mpl.figure.prototype.send_draw_message = function() {
if (!this.waiting) {
this.waiting = true;
this.ws.send(JSON.stringify({type: "draw", figure_id: this.id}));
}
}
mpl.figure.prototype.handle_save = function(fig, msg) {
var format_dropdown = fig.format_dropdown;
var format = format_dropdown.options[format_dropdown.selectedIndex].value;
fig.ondownload(fig, format);
}
mpl.figure.prototype.handle_resize = function(fig, msg) {
var size = msg['size'];
if (size[0] != fig.canvas.width || size[1] != fig.canvas.height) {
fig._resize_canvas(size[0], size[1]);
fig.send_message("refresh", {});
};
}
mpl.figure.prototype.handle_rubberband = function(fig, msg) {
var x0 = msg['x0'] / mpl.ratio;
var y0 = (fig.canvas.height - msg['y0']) / mpl.ratio;
var x1 = msg['x1'] / mpl.ratio;
var y1 = (fig.canvas.height - msg['y1']) / mpl.ratio;
x0 = Math.floor(x0) + 0.5;
y0 = Math.floor(y0) + 0.5;
x1 = Math.floor(x1) + 0.5;
y1 = Math.floor(y1) + 0.5;
var min_x = Math.min(x0, x1);
var min_y = Math.min(y0, y1);
var width = Math.abs(x1 - x0);
var height = Math.abs(y1 - y0);
fig.rubberband_context.clearRect(
0, 0, fig.canvas.width, fig.canvas.height);
fig.rubberband_context.strokeRect(min_x, min_y, width, height);
}
mpl.figure.prototype.handle_figure_label = function(fig, msg) {
// Updates the figure title.
fig.header.textContent = msg['label'];
}
mpl.figure.prototype.handle_cursor = function(fig, msg) {
var cursor = msg['cursor'];
switch(cursor)
{
case 0:
cursor = 'pointer';
break;
case 1:
cursor = 'default';
break;
case 2:
cursor = 'crosshair';
break;
case 3:
cursor = 'move';
break;
}
fig.rubberband_canvas.style.cursor = cursor;
}
mpl.figure.prototype.handle_message = function(fig, msg) {
fig.message.textContent = msg['message'];
}
mpl.figure.prototype.handle_draw = function(fig, msg) {
// Request the server to send over a new figure.
fig.send_draw_message();
}
mpl.figure.prototype.handle_image_mode = function(fig, msg) {
fig.image_mode = msg['mode'];
}
mpl.figure.prototype.updated_canvas_event = function() {
// Called whenever the canvas gets updated.
this.send_message("ack", {});
}
// A function to construct a web socket function for onmessage handling.
// Called in the figure constructor.
mpl.figure.prototype._make_on_message_function = function(fig) {
return function socket_on_message(evt) {
if (evt.data instanceof Blob) {
/* FIXME: We get "Resource interpreted as Image but
* transferred with MIME type text/plain:" errors on
* Chrome. But how to set the MIME type? It doesn't seem
* to be part of the websocket stream */
evt.data.type = "image/png";
/* Free the memory for the previous frames */
if (fig.imageObj.src) {
(window.URL || window.webkitURL).revokeObjectURL(
fig.imageObj.src);
}
fig.imageObj.src = (window.URL || window.webkitURL).createObjectURL(
evt.data);
fig.updated_canvas_event();
fig.waiting = false;
return;
}
else if (typeof evt.data === 'string' && evt.data.slice(0, 21) == "data:image/png;base64") {
fig.imageObj.src = evt.data;
fig.updated_canvas_event();
fig.waiting = false;
return;
}
var msg = JSON.parse(evt.data);
var msg_type = msg['type'];
// Call the "handle_{type}" callback, which takes
// the figure and JSON message as its only arguments.
try {
var callback = fig["handle_" + msg_type];
} catch (e) {
console.log("No handler for the '" + msg_type + "' message type: ", msg);
return;
}
if (callback) {
try {
// console.log("Handling '" + msg_type + "' message: ", msg);
callback(fig, msg);
} catch (e) {
console.log("Exception inside the 'handler_" + msg_type + "' callback:", e, e.stack, msg);
}
}
};
}
// from http://stackoverflow.com/questions/1114465/getting-mouse-location-in-canvas
mpl.findpos = function(e) {
//this section is from http://www.quirksmode.org/js/events_properties.html
var targ;
if (!e)
e = window.event;
if (e.target)
targ = e.target;
else if (e.srcElement)
targ = e.srcElement;
if (targ.nodeType == 3) // defeat Safari bug
targ = targ.parentNode;
// jQuery normalizes the pageX and pageY
// pageX,Y are the mouse positions relative to the document
// offset() returns the position of the element relative to the document
var x = e.pageX - $(targ).offset().left;
var y = e.pageY - $(targ).offset().top;
return {"x": x, "y": y};
};
/*
* return a copy of an object with only non-object keys
* we need this to avoid circular references
* http://stackoverflow.com/a/24161582/3208463
*/
function simpleKeys (original) {
return Object.keys(original).reduce(function (obj, key) {
if (typeof original[key] !== 'object')
obj[key] = original[key]
return obj;
}, {});
}
mpl.figure.prototype.mouse_event = function(event, name) {
var canvas_pos = mpl.findpos(event)
if (name === 'button_press')
{
this.canvas.focus();
this.canvas_div.focus();
}
var x = canvas_pos.x * mpl.ratio;
var y = canvas_pos.y * mpl.ratio;
this.send_message(name, {x: x, y: y, button: event.button,
step: event.step,
guiEvent: simpleKeys(event)});
/* This prevents the web browser from automatically changing to
* the text insertion cursor when the button is pressed. We want
* to control all of the cursor setting manually through the
* 'cursor' event from matplotlib */
event.preventDefault();
return false;
}
mpl.figure.prototype._key_event_extra = function(event, name) {
// Handle any extra behaviour associated with a key event
}
mpl.figure.prototype.key_event = function(event, name) {
// Prevent repeat events
if (name == 'key_press')
{
if (event.which === this._key)
return;
else
this._key = event.which;
}
if (name == 'key_release')
this._key = null;
var value = '';
if (event.ctrlKey && event.which != 17)
value += "ctrl+";