forked from UWPCE-PythonCert/IntroToPython-2014
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathsession05.html
More file actions
976 lines (873 loc) · 75.2 KB
/
session05.html
File metadata and controls
976 lines (873 loc) · 75.2 KB
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
<!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Session Five: Advanced Argument passing, List and Dict Comprehensions, Lambda and Functional programming — Introduction To Python 1.3 documentation</title>
<link href='https://fonts.googleapis.com/css?family=Lato:400,700|Roboto+Slab:400,700|Inconsolata:400,700' rel='stylesheet' type='text/css'>
<link rel="stylesheet" href="_static/css/theme.css" type="text/css" />
<link rel="top" title="Introduction To Python 1.3 documentation" href="index.html"/>
<link rel="next" title="Session Six: Object oriented programming: Classes, instances, attributes, and subclassing" href="session06.html"/>
<link rel="prev" title="Session Four: Dictionaries, Sets, Exceptions, and Files" href="session04.html"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/modernizr/2.6.2/modernizr.min.js"></script>
</head>
<body class="wy-body-for-nav" role="document">
<div class="wy-grid-for-nav">
<nav data-toggle="wy-nav-shift" class="wy-nav-side">
<div class="wy-side-nav-search">
<a href="index.html" class="fa fa-home"> Introduction To Python</a>
<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="main navigation">
<ul class="current">
<li class="toctree-l1"><a class="reference internal" href="session01.html">Session One: Introductions</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session01.html#introductions">Introductions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#introduction-to-this-class">Introduction to This Class</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#introduction-to-your-environment">Introduction to Your Environment</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#setting-up-your-environment">Setting Up Your Environment</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#introduction-to-ipython">Introduction to iPython</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#basic-python-syntax">Basic Python Syntax</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#id2">Homework</a></li>
<li class="toctree-l2"><a class="reference internal" href="session01.html#next-class">Next Class</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="session02.html">Session Two: Functions, Booleans and Modules</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session02.html#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#class-outline">Class Outline</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#first-a-little-git-primer">First a little git Primer...</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#quick-intro-to-basics">Quick Intro to Basics</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#break-time">BREAK TIME</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#functions">Functions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#boolean-expressions">Boolean Expressions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#in-class-lab">In-Class Lab:</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#id1">BREAK TIME</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#code-structure-modules-and-namespaces">Code Structure, Modules, and Namespaces</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#id3">In-Class Lab</a></li>
<li class="toctree-l2"><a class="reference internal" href="session02.html#homework">Homework</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="session03.html">Session Three: Sequences, Iteration and String Formatting</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session03.html#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#sequences">Sequences</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#lists-tuples">Lists, Tuples...</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#mutability">Mutability</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#mutable-sequence-methods">Mutable Sequence Methods</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#id1">Iteration</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#string-features">String Features</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#one-last-trick">One Last Trick</a></li>
<li class="toctree-l2"><a class="reference internal" href="session03.html#homework">Homework</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="session04.html">Session Four: Dictionaries, Sets, Exceptions, and Files</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session04.html#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session04.html#a-little-warm-up">A little warm up</a></li>
<li class="toctree-l2"><a class="reference internal" href="session04.html#dictionaries-and-sets">Dictionaries and Sets</a></li>
<li class="toctree-l2"><a class="reference internal" href="session04.html#exceptions">Exceptions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session04.html#file-reading-and-writing">File Reading and Writing</a></li>
<li class="toctree-l2"><a class="reference internal" href="session04.html#paths-and-directories">Paths and Directories</a></li>
<li class="toctree-l2"><a class="reference internal" href="session04.html#homework">Homework</a></li>
</ul>
</li>
<li class="toctree-l1 current"><a class="current reference internal" href="">Session Five: Advanced Argument passing, List and Dict Comprehensions, Lambda and Functional programming</a><ul>
<li class="toctree-l2"><a class="reference internal" href="#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="#advanced-argument-passing">Advanced Argument Passing</a></li>
<li class="toctree-l2"><a class="reference internal" href="#a-bit-more-on-mutability-and-copies">A bit more on mutability (and copies)</a></li>
<li class="toctree-l2"><a class="reference internal" href="#list-and-dict-comprehensions">List and Dict Comprehensions</a></li>
<li class="toctree-l2"><a class="reference internal" href="#anonymous-functions">Anonymous functions</a></li>
<li class="toctree-l2"><a class="reference internal" href="#functional-programming">Functional Programming</a></li>
<li class="toctree-l2"><a class="reference internal" href="#homework">Homework</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="session06.html">Session Six: Object oriented programming: Classes, instances, attributes, and subclassing</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session06.html#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session06.html#object-oriented-programming">Object Oriented Programming</a></li>
<li class="toctree-l2"><a class="reference internal" href="session06.html#python-classes">Python Classes</a></li>
<li class="toctree-l2"><a class="reference internal" href="session06.html#subclassing-inheritance">Subclassing/Inheritance</a></li>
<li class="toctree-l2"><a class="reference internal" href="session06.html#more-on-subclassing">More on Subclassing</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="session07.html">Session Seven: Testing, More OO</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session07.html#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session07.html#testing">Testing</a></li>
<li class="toctree-l2"><a class="reference internal" href="session07.html#more-on-subclassing">More on Subclassing</a></li>
<li class="toctree-l2"><a class="reference internal" href="session07.html#properties">Properties</a></li>
<li class="toctree-l2"><a class="reference internal" href="session07.html#static-and-class-methods">Static and Class Methods</a></li>
<li class="toctree-l2"><a class="reference internal" href="session07.html#special-methods">Special Methods</a></li>
<li class="toctree-l2"><a class="reference internal" href="session07.html#homework">Homework</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="session08.html">Session Eight: Generators, Iterators, Decorators, and Context Managers</a><ul>
<li class="toctree-l2"><a class="reference internal" href="session08.html#review-questions">Review/Questions</a></li>
<li class="toctree-l2"><a class="reference internal" href="session08.html#decorators">Decorators</a></li>
<li class="toctree-l2"><a class="reference internal" href="session08.html#iterators-and-generators">Iterators and Generators</a></li>
<li class="toctree-l2"><a class="reference internal" href="session08.html#context-managers">Context Managers</a></li>
<li class="toctree-l2"><a class="reference internal" href="session08.html#homework">Homework</a></li>
</ul>
</li>
</ul>
<ul>
<li class="toctree-l1"><a class="reference internal" href="homework/index.html">Homework Materials</a><ul>
<li class="toctree-l2"><a class="reference internal" href="homework/kata_fourteen.html">Kata Fourteen: Tom Swift Under Milk Wood</a></li>
<li class="toctree-l2"><a class="reference internal" href="homework/html_builder.html">HTML Renderer Homework Assignment</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="supplements/index.html">Supplemental Materials</a><ul>
<li class="toctree-l2"><a class="reference internal" href="supplements/python_learning_resources.html">Useful Python Learning Resources</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/python_for_mac.html">Setting up your Mac for Python and this class</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/python_for_windows.html">Setting up Windows for Python and this class</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/python_for_linux.html">Setting up Linux for Python and this class</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/virtualenv.html">Working with Virtualenv</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/sublime_as_ide.html">Turning Sublime Text Into a Lightweight Python IDE</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/shell.html">Shell Customizations for Python Development</a></li>
<li class="toctree-l2"><a class="reference internal" href="supplements/unicode.html">Unicode in Python 2</a></li>
</ul>
</li>
</ul>
</div>
</nav>
<section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">
<nav class="wy-nav-top" role="navigation" aria-label="top navigation">
<i data-toggle="wy-nav-top" class="fa fa-bars"></i>
<a href="index.html">Introduction To Python</a>
</nav>
<div class="wy-nav-content">
<div class="rst-content">
<div role="navigation" aria-label="breadcrumbs navigation">
<ul class="wy-breadcrumbs">
<li><a href="index.html">Docs</a> »</li>
<li>Session Five: Advanced Argument passing, List and Dict Comprehensions, Lambda and Functional programming</li>
<li class="wy-breadcrumbs-aside">
<a href="_sources/session05.txt" rel="nofollow"> View page source</a>
</li>
</ul>
<hr/>
</div>
<div role="main">
<div class="section" id="session-five-advanced-argument-passing-list-and-dict-comprehensions-lambda-and-functional-programming">
<h1>Session Five: Advanced Argument passing, List and Dict Comprehensions, Lambda and Functional programming<a class="headerlink" href="#session-five-advanced-argument-passing-list-and-dict-comprehensions-lambda-and-functional-programming" title="Permalink to this headline">¶</a></h1>
<div class="section" id="review-questions">
<h2>Review/Questions<a class="headerlink" href="#review-questions" title="Permalink to this headline">¶</a></h2>
<div class="section" id="review-of-previous-class">
<h3>Review of Previous Class<a class="headerlink" href="#review-of-previous-class" title="Permalink to this headline">¶</a></h3>
<blockquote>
<div><ul class="simple">
<li>Dictionaries</li>
<li>Exceptions</li>
<li>Files, etc.</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="homework-review">
<h3>Homework review<a class="headerlink" href="#homework-review" title="Permalink to this headline">¶</a></h3>
<p>Homework Questions?</p>
<p>My Solutions to the dict/set lab, and some others in the class repo in: <tt class="docutils literal"><span class="pre">Solutions</span></tt></p>
<p>A few tidbits:</p>
<p>dicts aren’t sorted, so what if you want to do something in a sorted way?</p>
<p>The “old” way:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">keys</span> <span class="o">=</span> <span class="n">d</span><span class="o">.</span><span class="n">keys</span><span class="p">()</span>
<span class="n">keys</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span>
<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">keys</span><span class="p">:</span>
<span class="o">...</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="n">collections</span><span class="o">.</span><span class="n">OrderedDict</span>
<span class="nb">sorted</span><span class="p">()</span>
</pre></div>
</div>
<p>(demo)</p>
</div>
</div>
<div class="section" id="advanced-argument-passing">
<h2>Advanced Argument Passing<a class="headerlink" href="#advanced-argument-passing" title="Permalink to this headline">¶</a></h2>
<div class="section" id="keyword-arguments">
<h3>Keyword arguments<a class="headerlink" href="#keyword-arguments" title="Permalink to this headline">¶</a></h3>
<p>When defining a function, you can specify only what you need – in any order</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [151]: </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span><span class="n">z</span><span class="o">=</span><span class="mi">0</span><span class="p">):</span>
<span class="go"> print x,y,z</span>
<span class="gp"> .....:</span>
<span class="gp">In [152]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">)</span>
<span class="go">1 2 3</span>
<span class="gp">In [153]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">z</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
<span class="go">1 0 3</span>
<span class="gp">In [154]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">z</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">y</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span>
<span class="go">1 2 3</span>
</pre></div>
</div>
<p>A Common Idiom:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
<span class="k">if</span> <span class="n">y</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
<span class="n">do_something_different</span>
<span class="n">go_on_here</span>
</pre></div>
</div>
<p>Can set defaults to variables</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [156]: </span><span class="n">y</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">In [157]: </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="o">=</span><span class="n">y</span><span class="p">):</span>
<span class="go"> print "x is:", x</span>
<span class="gp"> .....:</span>
<span class="gp">In [158]: </span><span class="n">fun</span><span class="p">()</span>
<span class="go">x is: 4</span>
</pre></div>
</div>
<p>Defaults are evaluated when the function is defined</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [156]: </span><span class="n">y</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">In [157]: </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="o">=</span><span class="n">y</span><span class="p">):</span>
<span class="go"> print "x is:", x</span>
<span class="gp"> .....:</span>
<span class="gp">In [158]: </span><span class="n">fun</span><span class="p">()</span>
<span class="go">x is: 4</span>
<span class="gp">In [159]: </span><span class="n">y</span> <span class="o">=</span> <span class="mi">6</span>
<span class="gp">In [160]: </span><span class="n">fun</span><span class="p">()</span>
<span class="go">x is: 4</span>
</pre></div>
</div>
</div>
<div class="section" id="function-arguments-in-variables">
<h3>Function arguments in variables<a class="headerlink" href="#function-arguments-in-variables" title="Permalink to this headline">¶</a></h3>
<p>function arguments are really just</p>
<ul class="simple">
<li>a tuple (positional arguments)</li>
<li>a dict (keyword arguments)</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">f</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="n">w</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">h</span><span class="o">=</span><span class="mi">0</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"position: </span><span class="si">%s</span><span class="s">, </span><span class="si">%s</span><span class="s"> -- shape: </span><span class="si">%s</span><span class="s">, </span><span class="si">%s</span><span class="s">"</span><span class="o">%</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="n">w</span><span class="p">,</span> <span class="n">h</span><span class="p">)</span>
<span class="n">position</span> <span class="o">=</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span>
<span class="n">size</span> <span class="o">=</span> <span class="p">{</span><span class="s">'h'</span><span class="p">:</span> <span class="mi">10</span><span class="p">,</span> <span class="s">'w'</span><span class="p">:</span> <span class="mi">20</span><span class="p">}</span>
<span class="o">>>></span> <span class="n">f</span><span class="p">(</span> <span class="o">*</span><span class="n">position</span><span class="p">,</span> <span class="o">**</span><span class="n">size</span><span class="p">)</span>
<span class="n">position</span><span class="p">:</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span> <span class="o">--</span> <span class="n">shape</span><span class="p">:</span> <span class="mi">20</span><span class="p">,</span> <span class="mi">10</span>
</pre></div>
</div>
</div>
<div class="section" id="function-parameters-in-variables">
<h3>Function parameters in variables<a class="headerlink" href="#function-parameters-in-variables" title="Permalink to this headline">¶</a></h3>
<p>You can also pull the parameters out in the function as a tuple and a dict:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="go">def f(*args, **kwargs):</span>
<span class="go"> print "the positional arguments are:", args</span>
<span class="go"> print "the keyword arguments are:", kwargs</span>
<span class="gp">In [389]: </span><span class="n">f</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="n">this</span><span class="o">=</span><span class="mi">5</span><span class="p">,</span> <span class="n">that</span><span class="o">=</span><span class="mi">7</span><span class="p">)</span>
<span class="go">the positional arguments are: (2, 3)</span>
<span class="go">the keyword arguments are: {'this': 5, 'that': 7}</span>
</pre></div>
</div>
</div>
<div class="section" id="passing-a-dict-to-the-string-format-method">
<h3>Passing a dict to the <tt class="docutils literal"><span class="pre">string.format()</span></tt> method<a class="headerlink" href="#passing-a-dict-to-the-string-format-method" title="Permalink to this headline">¶</a></h3>
<p>Now that you know that keyword args are really a dict, you can do this nifty trick:</p>
<p>The <tt class="docutils literal"><span class="pre">format</span></tt> method takes keyword arguments:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [24]: </span><span class="s">u"My name is {first} {last}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">last</span><span class="o">=</span><span class="s">u"Barker"</span><span class="p">,</span> <span class="n">first</span><span class="o">=</span><span class="s">u"Chris"</span><span class="p">)</span>
<span class="gh">Out[24]: </span><span class="go">u'My name is Chris Barker'</span>
</pre></div>
</div>
<p>Build a dict of the keys and values:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [25]: </span><span class="n">d</span> <span class="o">=</span> <span class="p">{</span><span class="s">u"last"</span><span class="p">:</span><span class="s">u"Barker"</span><span class="p">,</span> <span class="s">u"first"</span><span class="p">:</span><span class="s">u"Chris"</span><span class="p">}</span>
</pre></div>
</div>
<p>And pass to <tt class="docutils literal"><span class="pre">format()``with</span> <span class="pre">``**</span></tt></p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [26]: </span><span class="s">u"My name is {first} {last}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="o">**</span><span class="n">d</span><span class="p">)</span>
<span class="gh">Out[26]: </span><span class="go">u'My name is Chris Barker'</span>
</pre></div>
</div>
</div>
<div class="section" id="lab">
<h3>LAB<a class="headerlink" href="#lab" title="Permalink to this headline">¶</a></h3>
<p>Let’s do this right now:</p>
<p>keyword arguments</p>
<ul class="simple">
<li>Write a function that has four optional parameters (with defaults):<ul>
<li>foreground_color</li>
<li>background_color</li>
<li>link_color</li>
<li>visited_link_color</li>
</ul>
</li>
<li>Have it print the colors (use strings for the colors)</li>
<li>Call it with a couple different parameters set</li>
<li>Have it pull the parameters out with <tt class="docutils literal"><span class="pre">*args,</span> <span class="pre">**kwargs</span></tt></li>
</ul>
</div>
</div>
<div class="section" id="a-bit-more-on-mutability-and-copies">
<h2>A bit more on mutability (and copies)<a class="headerlink" href="#a-bit-more-on-mutability-and-copies" title="Permalink to this headline">¶</a></h2>
<div class="section" id="mutable-objects">
<h3>mutable objects<a class="headerlink" href="#mutable-objects" title="Permalink to this headline">¶</a></h3>
<p>We’ve talked about this: mutable objects can have their contents changed in place.</p>
<p>Immutable objects can not.</p>
<p>This has implications when you have a container with mutable objects in it:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [28]: </span><span class="n">list1</span> <span class="o">=</span> <span class="p">[</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="s">'a'</span><span class="p">,</span><span class="s">'b'</span><span class="p">]</span> <span class="p">]</span>
</pre></div>
</div>
<p>one way to make a copy of a list:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [29]: </span><span class="n">list2</span> <span class="o">=</span> <span class="n">list1</span><span class="p">[:]</span>
<span class="gp">In [30]: </span><span class="n">list2</span> <span class="ow">is</span> <span class="n">list1</span>
<span class="gh">Out[30]: </span><span class="go">False</span>
</pre></div>
</div>
<p>they are different lists.</p>
<p>What if we set an element to a new value?</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [31]: </span><span class="n">list1</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="p">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">]</span>
<span class="gp">In [32]: </span><span class="n">list1</span>
<span class="gh">Out[32]: </span><span class="go">[[5, 6, 7], ['a', 'b']]</span>
<span class="gp">In [33]: </span><span class="n">list2</span>
<span class="gh">Out[33]: </span><span class="go">[[1, 2, 3], ['a', 'b']]</span>
</pre></div>
</div>
<p>So they are independent.</p>
<p>But what if we mutate an element?</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [34]: </span><span class="n">list1</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s">'c'</span><span class="p">)</span>
<span class="gp">In [35]: </span><span class="n">list1</span>
<span class="gh">Out[35]: </span><span class="go">[[5, 6, 7], ['a', 'b', 'c']]</span>
<span class="gp">In [36]: </span><span class="n">list2</span>
<span class="gh">Out[36]: </span><span class="go">[[1, 2, 3], ['a', 'b', 'c']]</span>
</pre></div>
</div>
<p>uuh oh! mutating an element in one list mutated the one in the other list.</p>
<p>Why is that?</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [38]: </span><span class="n">list1</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="ow">is</span> <span class="n">list2</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
<span class="gh">Out[38]: </span><span class="go">True</span>
</pre></div>
</div>
<p>The elements are the same object!</p>
<p>This is known as a “shallow” copy – Python doesn’t want to copy more than it needs to, so in this case, it makes a new list, but does not make copies of the contents.</p>
<p>Same for dicts (and any container type)</p>
<p>If the elements are immutable, it doesn’t really make a differnce – but be very careful with mutable elements.</p>
</div>
<div class="section" id="the-copy-module">
<h3>The copy module<a class="headerlink" href="#the-copy-module" title="Permalink to this headline">¶</a></h3>
<p>most objects have a way to make copies (<tt class="docutils literal"><span class="pre">dict.copy()</span></tt> for instance).</p>
<p>but if not, you can use the <tt class="docutils literal"><span class="pre">copy</span></tt> module to make a copy:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [39]: </span><span class="kn">import</span> <span class="nn">copy</span>
<span class="gp">In [40]: </span><span class="n">list3</span> <span class="o">=</span> <span class="n">copy</span><span class="o">.</span><span class="n">copy</span><span class="p">(</span><span class="n">list2</span><span class="p">)</span>
<span class="gp">In [41]: </span><span class="n">list3</span>
<span class="gh">Out[41]: </span><span class="go">[[1, 2, 3], ['a', 'b', 'c']]</span>
</pre></div>
</div>
<p>This is also a shallow copy.</p>
<p>But there is another option:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [3]: </span><span class="n">list1</span>
<span class="gh">Out[3]: </span><span class="go">[[1, 2, 3], ['a', 'b', 'c']]</span>
<span class="gp">In [4]: </span><span class="n">list2</span> <span class="o">=</span> <span class="n">copy</span><span class="o">.</span><span class="n">deepcopy</span><span class="p">(</span><span class="n">list1</span><span class="p">)</span>
<span class="gp">In [5]: </span><span class="n">list1</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="gp">In [6]: </span><span class="n">list1</span>
<span class="gh">Out[6]: </span><span class="go">[[1, 2, 3, 4], ['a', 'b', 'c']]</span>
<span class="gp">In [7]: </span><span class="n">list2</span>
<span class="gh">Out[7]: </span><span class="go">[[1, 2, 3], ['a', 'b', 'c']]</span>
</pre></div>
</div>
<p><tt class="docutils literal"><span class="pre">deepcopy</span></tt> recurses through the object, making copies of everything as it goes.</p>
<p>I happened on this thread on stack overflow:</p>
<p><a class="reference external" href="http://stackoverflow.com/questions/3975376/understanding-dict-copy-shallow-or-deep">http://stackoverflow.com/questions/3975376/understanding-dict-copy-shallow-or-deep</a></p>
<p>The OP is pretty confused – can you sort it out?</p>
<p>Make sure you understand the difference between a reference, a shallow copy, and a deep copy.</p>
</div>
<div class="section" id="mutables-as-default-arguments">
<h3>Mutables as default arguments:<a class="headerlink" href="#mutables-as-default-arguments" title="Permalink to this headline">¶</a></h3>
<p>Another “gotcha” is using mutables as default arguments:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [11]: </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">a</span><span class="o">=</span><span class="p">[]):</span>
<span class="gp"> ....: </span> <span class="n">a</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="gp"> ....: </span> <span class="k">print</span> <span class="n">a</span>
<span class="gp"> ....:</span>
</pre></div>
</div>
<p>This makes sense: maybe you’d pass in a list, but the default is an empty list.</p>
<p>But:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [12]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="go">[3]</span>
<span class="gp">In [13]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="go">[3, 4]</span>
</pre></div>
</div>
<p>Huh?!</p>
<p>Remember that that default argument is defined when the function is created: there will be only one list, and every time the function is called, that same list is used.</p>
<p>The solution:</p>
<p>The standard practice for such a mutable default argument:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [15]: </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">a</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
<span class="gp"> ....: </span> <span class="k">if</span> <span class="n">a</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
<span class="gp"> ....: </span> <span class="n">a</span> <span class="o">=</span> <span class="p">[]</span>
<span class="gp"> ....: </span> <span class="n">a</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="gp"> ....: </span> <span class="k">print</span> <span class="n">a</span>
<span class="gp">In [16]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="go">[3]</span>
<span class="gp">In [17]: </span><span class="n">fun</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="go">[4]</span>
</pre></div>
</div>
<p>You get a new list every time the function is called</p>
</div>
</div>
<div class="section" id="list-and-dict-comprehensions">
<h2>List and Dict Comprehensions<a class="headerlink" href="#list-and-dict-comprehensions" title="Permalink to this headline">¶</a></h2>
<div class="section" id="list-comprehensions">
<h3>List comprehensions<a class="headerlink" href="#list-comprehensions" title="Permalink to this headline">¶</a></h3>
<p>A bit of functional programming</p>
<p>consider this common for loop structure:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_list</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">variable</span> <span class="ow">in</span> <span class="n">a_list</span><span class="p">:</span>
<span class="n">new_list</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">expression</span><span class="p">)</span>
</pre></div>
</div>
<p>This can be expressed with a single line using a “list comprehension”</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_list</span> <span class="o">=</span> <span class="p">[</span><span class="n">expression</span> <span class="k">for</span> <span class="n">variable</span> <span class="ow">in</span> <span class="n">a_list</span><span class="p">]</span>
</pre></div>
</div>
<p>What about nested for loops?</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_list</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">var</span> <span class="ow">in</span> <span class="n">a_list</span><span class="p">:</span>
<span class="k">for</span> <span class="n">var2</span> <span class="ow">in</span> <span class="n">a_list2</span><span class="p">:</span>
<span class="n">new_list</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">expression</span><span class="p">)</span>
</pre></div>
</div>
<p>Can also be expressed in one line:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_list</span> <span class="o">=</span> <span class="p">[</span><span class="n">exp</span> <span class="k">for</span> <span class="n">var</span> <span class="ow">in</span> <span class="n">a_list</span> <span class="k">for</span> <span class="n">var2</span> <span class="ow">in</span> <span class="n">a_list2</span><span class="p">]</span>
</pre></div>
</div>
<p>You get the “outer product”, i.e. all combinations.</p>
<p>(demo)</p>
<p>But usually you at least have a conditional in the loop:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_list</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">variable</span> <span class="ow">in</span> <span class="n">a_list</span><span class="p">:</span>
<span class="k">if</span> <span class="n">something_is_true</span><span class="p">:</span>
<span class="n">new_list</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">expression</span><span class="p">)</span>
</pre></div>
</div>
<p>You can add a conditional to the comprehension:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_list</span> <span class="o">=</span> <span class="p">[</span><span class="n">expr</span> <span class="k">for</span> <span class="n">var</span> <span class="ow">in</span> <span class="n">a_list</span> <span class="k">if</span> <span class="n">something_is_true</span><span class="p">]</span>
</pre></div>
</div>
<p>(demo)</p>
<p>Examples:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [341]: </span><span class="p">[</span><span class="n">x</span><span class="o">**</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">3</span><span class="p">)]</span>
<span class="gh">Out[341]: </span><span class="go">[0, 1, 4]</span>
<span class="gp">In [342]: </span><span class="p">[</span><span class="n">x</span><span class="o">+</span><span class="n">y</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span> <span class="k">for</span> <span class="n">y</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">)]</span>
<span class="gh">Out[342]: </span><span class="go">[5, 6, 6, 7, 7, 8]</span>
<span class="gp">In [343]: </span><span class="p">[</span><span class="n">x</span><span class="o">*</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">6</span><span class="p">)</span> <span class="k">if</span> <span class="ow">not</span> <span class="n">x</span><span class="o">%</span><span class="k">2</span><span class="p">]</span>
<span class="gh">Out[343]: </span><span class="go">[0, 4, 8]</span>
</pre></div>
</div>
<p>Remember this from last week?</p>
<div class="highlight-python"><div class="highlight"><pre><span class="p">[</span><span class="n">name</span> <span class="k">for</span> <span class="n">name</span> <span class="ow">in</span> <span class="nb">dir</span><span class="p">(</span><span class="n">__builtin__</span><span class="p">)</span> <span class="k">if</span> <span class="s">"Error"</span> <span class="ow">in</span> <span class="n">name</span><span class="p">]</span>
<span class="p">[</span><span class="s">'ArithmeticError'</span><span class="p">,</span>
<span class="s">'AssertionError'</span><span class="p">,</span>
<span class="s">'AttributeError'</span><span class="p">,</span>
<span class="s">'BufferError'</span><span class="p">,</span>
<span class="s">'EOFError'</span><span class="p">,</span>
<span class="o">....</span>
</pre></div>
</div>
</div>
<div class="section" id="set-comprehensions">
<h3>Set Comprehensions<a class="headerlink" href="#set-comprehensions" title="Permalink to this headline">¶</a></h3>
<p>You can do it with sets, too:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_set</span> <span class="o">=</span> <span class="p">{</span> <span class="n">value</span> <span class="k">for</span> <span class="n">variable</span> <span class="ow">in</span> <span class="n">a_sequence</span> <span class="p">}</span>
</pre></div>
</div>
<p>same as for loop:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_set</span> <span class="o">=</span> <span class="nb">set</span><span class="p">()</span>
<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">a_list</span><span class="p">:</span>
<span class="n">new_set</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
</pre></div>
</div>
<p>Example: finding all the vowels in a string...</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [19]: </span><span class="n">s</span> <span class="o">=</span> <span class="s">"a not very long string"</span>
<span class="gp">In [20]: </span><span class="n">vowels</span> <span class="o">=</span> <span class="nb">set</span><span class="p">(</span><span class="s">'aeiou'</span><span class="p">)</span>
<span class="gp">In [21]: </span><span class="p">{</span> <span class="n">let</span> <span class="k">for</span> <span class="n">let</span> <span class="ow">in</span> <span class="n">s</span> <span class="k">if</span> <span class="n">let</span> <span class="ow">in</span> <span class="n">vowels</span> <span class="p">}</span>
<span class="gh">Out[21]: </span><span class="go">{'a', 'e', 'i', 'o'}</span>
</pre></div>
</div>
<p>Side note: why did I do <tt class="docutils literal"><span class="pre">set('aeiou')</span></tt> rather than just <cite>aeiou</cite> ?</p>
</div>
<div class="section" id="dict-comprehensions">
<h3>Dict Comprehensions<a class="headerlink" href="#dict-comprehensions" title="Permalink to this headline">¶</a></h3>
<p>Also with dictionaries</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_dict</span> <span class="o">=</span> <span class="p">{</span> <span class="n">key</span><span class="p">:</span><span class="n">value</span> <span class="k">for</span> <span class="n">variable</span> <span class="ow">in</span> <span class="n">a_sequence</span><span class="p">}</span>
</pre></div>
</div>
<p>same as for loop:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">new_dict</span> <span class="o">=</span> <span class="p">{}</span>
<span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">a_list</span><span class="p">:</span>
<span class="n">new_dict</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">value</span>
</pre></div>
</div>
<p>Example</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [22]: </span><span class="p">{</span> <span class="n">i</span><span class="p">:</span> <span class="s">"this_</span><span class="si">%i</span><span class="s">"</span><span class="o">%</span><span class="k">i</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span> <span class="p">}</span>
<span class="gh">Out[22]: </span><span class="go">{0: 'this_0', 1: 'this_1', 2: 'this_2',</span>
<span class="go"> 3: 'this_3', 4: 'this_4'}</span>
</pre></div>
</div>
<p>(not as useful with the <tt class="docutils literal"><span class="pre">dict()</span></tt> constructor...)</p>
</div>
</div>
<div class="section" id="anonymous-functions">
<h2>Anonymous functions<a class="headerlink" href="#anonymous-functions" title="Permalink to this headline">¶</a></h2>
<div class="section" id="lambda">
<h3>lambda<a class="headerlink" href="#lambda" title="Permalink to this headline">¶</a></h3>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [171]: </span><span class="n">f</span> <span class="o">=</span> <span class="k">lambda</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span>
<span class="gp">In [172]: </span><span class="n">f</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">)</span>
<span class="gh">Out[172]: </span><span class="go">5</span>
</pre></div>
</div>
<p>Content can only be an expression – not a statement</p>
<p>Anyone remember what the difference is?</p>
<p>Called “Anonymous”: it doesn’t need a name.</p>
<p>It’s a python object, it can be stored in a list or other container</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [7]: </span><span class="n">l</span> <span class="o">=</span> <span class="p">[</span><span class="k">lambda</span> <span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="p">]</span>
<span class="gp">In [8]: </span><span class="nb">type</span><span class="p">(</span><span class="n">l</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="gh">Out[8]: </span><span class="go">function</span>
</pre></div>
</div>
<p>And you can call it:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [9]: </span><span class="n">l</span><span class="p">[</span><span class="mi">0</span><span class="p">](</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span>
<span class="gh">Out[9]: </span><span class="go">7</span>
</pre></div>
</div>
</div>
<div class="section" id="functions-as-first-class-objects">
<h3>Functions as first class objects<a class="headerlink" href="#functions-as-first-class-objects" title="Permalink to this headline">¶</a></h3>
<p>You can do that with “regular” functions too:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [12]: </span><span class="k">def</span> <span class="nf">fun</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="gp"> ....: </span> <span class="k">return</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span>
<span class="gp"> ....:</span>
<span class="gp">In [13]: </span><span class="n">l</span> <span class="o">=</span> <span class="p">[</span><span class="n">fun</span><span class="p">]</span>
<span class="gp">In [14]: </span><span class="nb">type</span><span class="p">(</span><span class="n">l</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="gh">Out[14]: </span><span class="go">function</span>
<span class="gp">In [15]: </span><span class="n">l</span><span class="p">[</span><span class="mi">0</span><span class="p">](</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">)</span>
<span class="gh">Out[15]: </span><span class="go">7</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="functional-programming">
<h2>Functional Programming<a class="headerlink" href="#functional-programming" title="Permalink to this headline">¶</a></h2>
<div class="section" id="map">
<h3>map<a class="headerlink" href="#map" title="Permalink to this headline">¶</a></h3>
<p><tt class="docutils literal"><span class="pre">map</span></tt> “maps” a function onto a sequence of objects – It applies the function to each item in the list, returning another list</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [23]: </span><span class="n">l</span> <span class="o">=</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">12</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<span class="gp">In [24]: </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
<span class="go"> return x*2 + 10</span>
<span class="gp">In [25]: </span><span class="nb">map</span><span class="p">(</span><span class="n">fun</span><span class="p">,</span> <span class="n">l</span><span class="p">)</span>
<span class="gh">Out[25]: </span><span class="go">[14, 20, 24, 34, 22, 18]</span>
</pre></div>
</div>
<p>But if it’s a small function, and you only need it once:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [26]: </span><span class="nb">map</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="n">x</span><span class="o">*</span><span class="mi">2</span> <span class="o">+</span> <span class="mi">10</span><span class="p">,</span> <span class="n">l</span><span class="p">)</span>
<span class="gh">Out[26]: </span><span class="go">[14, 20, 24, 34, 22, 18]</span>
</pre></div>
</div>
</div>
<div class="section" id="filter">
<h3>filter<a class="headerlink" href="#filter" title="Permalink to this headline">¶</a></h3>
<p><tt class="docutils literal"><span class="pre">filter</span></tt> “filters” a sequence of objects with a boolean function –
It keeps only those for which the function is True</p>
<p>To get only the even numbers:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [27]: </span><span class="n">l</span> <span class="o">=</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">12</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<span class="gp">In [28]: </span><span class="nb">filter</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="ow">not</span> <span class="n">x</span><span class="o">%</span><span class="k">2</span><span class="p">,</span> <span class="n">l</span><span class="p">)</span>
<span class="gh">Out[28]: </span><span class="go">[2, 12, 6, 4]</span>
</pre></div>
</div>
</div>
<div class="section" id="reduce">
<h3>reduce<a class="headerlink" href="#reduce" title="Permalink to this headline">¶</a></h3>
<p><tt class="docutils literal"><span class="pre">reduce</span></tt> “reduces” a sequence of objects to a single object with a function that combines two arguments</p>
<p>To get the sum:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [30]: </span><span class="n">l</span> <span class="o">=</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">12</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<span class="gp">In [31]: </span><span class="nb">reduce</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="p">,</span> <span class="n">l</span><span class="p">)</span>
<span class="gh">Out[31]: </span><span class="go">36</span>
</pre></div>
</div>
<p>To get the product:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [32]: </span><span class="nb">reduce</span><span class="p">(</span><span class="k">lambda</span> <span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">*</span><span class="n">y</span><span class="p">,</span> <span class="n">l</span><span class="p">)</span>
<span class="gh">Out[32]: </span><span class="go">20160</span>
</pre></div>
</div>
</div>
<div class="section" id="comprehensions">
<h3>Comprehensions<a class="headerlink" href="#comprehensions" title="Permalink to this headline">¶</a></h3>
<p>Couldn’t you do all this with comprehensions?</p>
<p>Yes:</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [33]: </span><span class="p">[</span><span class="n">x</span><span class="o">+</span><span class="mi">2</span> <span class="o">+</span> <span class="mi">10</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">l</span><span class="p">]</span>
<span class="gh">Out[33]: </span><span class="go">[14, 17, 19, 24, 18, 16]</span>
<span class="gp">In [34]: </span><span class="p">[</span><span class="n">x</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">l</span> <span class="k">if</span> <span class="ow">not</span> <span class="n">x</span><span class="o">%</span><span class="k">2</span><span class="p">]</span>
<span class="gh">Out[34]: </span><span class="go">[2, 12, 6, 4]</span>
</pre></div>
</div>
<p>(Except Reduce)</p>
<p>But Guido thinks almost all uses of reduce are really <tt class="docutils literal"><span class="pre">sum()</span></tt></p>
</div>
<div class="section" id="id1">
<h3>Functional Programming<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h3>
<p>Comprehensions and map, filter, reduce are all “functional programming” approaches}</p>
<p><tt class="docutils literal"><span class="pre">map,</span> <span class="pre">filter</span></tt> and <tt class="docutils literal"><span class="pre">reduce</span></tt> pre-date comprehensions in Python’s history</p>
<p>Some people like that syntax better</p>
<p>And “map-reduce” is a big concept these days for parallel processing of “Big Data” in NoSQL databases.</p>
<p>(Hadoop, MongoDB, etc.)</p>
</div>
<div class="section" id="a-bit-more-about-lambda">
<h3>A bit more about lambda<a class="headerlink" href="#a-bit-more-about-lambda" title="Permalink to this headline">¶</a></h3>
<p>Can also use keyword arguments}</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [186]: </span><span class="n">l</span> <span class="o">=</span> <span class="p">[]</span>
<span class="gp">In [187]: </span><span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">3</span><span class="p">):</span>
<span class="go"> l.append(lambda x, e=i: x**e)</span>
<span class="gp"> .....:</span>
<span class="gp">In [189]: </span><span class="k">for</span> <span class="n">f</span> <span class="ow">in</span> <span class="n">l</span><span class="p">:</span>
<span class="go"> print f(3)</span>
<span class="go">1</span>
<span class="go">3</span>
<span class="go">9</span>
</pre></div>
</div>
<p>Note when the keyword argument is evaluated: this turns out to be very handy!</p>
</div>
</div>
<div class="section" id="homework">
<h2>Homework<a class="headerlink" href="#homework" title="Permalink to this headline">¶</a></h2>
<div class="section" id="id2">
<h3>List comprehensions<a class="headerlink" href="#id2" title="Permalink to this headline">¶</a></h3>
<p>Note: this is a bit of a “backwards” exercise –
we show you code, you figure out what it does.</p>
<p>As a result, not much to submit – but so we can give you credit, submit
a file with a solution to the final problem.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">feast</span> <span class="o">=</span> <span class="p">[</span><span class="s">'lambs'</span><span class="p">,</span> <span class="s">'sloths'</span><span class="p">,</span> <span class="s">'orangutans'</span><span class="p">,</span> <span class="s">'breakfast cereals'</span><span class="p">,</span> <span class="s">'fruit bats'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">comprehension</span> <span class="o">=</span> <span class="p">[</span><span class="n">delicacy</span><span class="o">.</span><span class="n">capitalize</span><span class="p">()</span> <span class="k">for</span> <span class="n">delicacy</span> <span class="ow">in</span> <span class="n">feast</span><span class="p">]</span>
</pre></div>
</div>
<p>What is the output of:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">comprehension</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="n">comprehension</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span>
<span class="go">???</span>
</pre></div>
</div>
<p>(figure it out before you try it)</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">feast</span> <span class="o">=</span> <span class="p">[</span><span class="s">'spam'</span><span class="p">,</span> <span class="s">'sloths'</span><span class="p">,</span> <span class="s">'orangutans'</span><span class="p">,</span> <span class="s">'breakfast cereals'</span><span class="p">,</span>
<span class="go"> 'fruit bats']</span>
<span class="gp">>>> </span><span class="n">comprehension</span> <span class="o">=</span> <span class="p">[</span><span class="n">delicacy</span> <span class="k">for</span> <span class="n">delicacy</span> <span class="ow">in</span> <span class="n">feast</span> <span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">delicacy</span><span class="p">)</span> <span class="o">></span> <span class="mi">6</span><span class="p">]</span>
</pre></div>
</div>
<p>What is the output of:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">feast</span><span class="p">)</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">comprehension</span><span class="p">)</span>
<span class="go">???</span>
</pre></div>
</div>
<p>(figure it out first!)</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">list_of_tuples</span> <span class="o">=</span> <span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="s">'lumberjack'</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="s">'inquisition'</span><span class="p">),</span> <span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="s">'spam'</span><span class="p">)]</span>
<span class="gp">>>> </span><span class="n">comprehension</span> <span class="o">=</span> <span class="p">[</span> <span class="n">skit</span> <span class="o">*</span> <span class="n">number</span> <span class="k">for</span> <span class="n">number</span><span class="p">,</span> <span class="n">skit</span> <span class="ow">in</span> <span class="n">list_of_tuples</span> <span class="p">]</span>
</pre></div>
</div>
<p>What is the output of:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">comprehension</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">comprehension</span><span class="p">[</span><span class="mi">2</span><span class="p">])</span>
<span class="go">???</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">list_of_eggs</span> <span class="o">=</span> <span class="p">[</span><span class="s">'poached egg'</span><span class="p">,</span> <span class="s">'fried egg'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">list_of_meats</span> <span class="o">=</span> <span class="p">[</span><span class="s">'lite spam'</span><span class="p">,</span> <span class="s">'ham spam'</span><span class="p">,</span> <span class="s">'fried spam'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">comprehension</span> <span class="o">=</span> <span class="p">[</span> <span class="s">'{0} and {1}'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">egg</span><span class="p">,</span> <span class="n">meat</span><span class="p">)</span> <span class="k">for</span> <span class="n">egg</span> <span class="ow">in</span> <span class="n">list_of_eggs</span> <span class="k">for</span> <span class="n">meat</span> <span class="ow">in</span> <span class="n">list_of_meats</span><span class="p">]</span>
</pre></div>
</div>
<p>What is the output of:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">comprehension</span><span class="p">)</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="n">comprehension</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="go">???</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">comprehension</span> <span class="o">=</span> <span class="p">{</span> <span class="n">x</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="s">'aabbbcccc'</span><span class="p">}</span>
</pre></div>
</div>
<p>What is the output of:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">comprehension</span>
<span class="go">???</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">dict_of_weapons</span> <span class="o">=</span> <span class="p">{</span><span class="s">'first'</span><span class="p">:</span> <span class="s">'fear'</span><span class="p">,</span>
<span class="go"> 'second': 'surprise',</span>
<span class="go"> 'third':'ruthless efficiency',</span>
<span class="go"> 'forth':'fanatical devotion',</span>
<span class="go"> 'fifth': None}</span>
<span class="gp">>>> </span><span class="n">dict_comprehension</span> <span class="o">=</span> \
<span class="go">{ k.upper(): weapon for k, weapon in dict_of_weapons.iteritems() if weapon}</span>
</pre></div>
</div>
<p>What is the output of:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="s">'first'</span> <span class="ow">in</span> <span class="n">dict_comprehension</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="s">'FIRST'</span> <span class="ow">in</span> <span class="n">dict_comprehension</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">dict_of_weapons</span><span class="p">)</span>
<span class="go">???</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">dict_comprehension</span><span class="p">)</span>
<span class="go">???</span>
</pre></div>
</div>
<p>See also:</p>
<p><a class="reference external" href="https://github.com/gregmalcolm/python_koans">https://github.com/gregmalcolm/python_koans</a></p>
<p><a class="reference external" href="https://github.com/gregmalcolm/python_koans/blob/master/python2/koans/about_comprehension.py">https://github.com/gregmalcolm/python_koans/blob/master/python2/koans/about_comprehension.py</a></p>
<p>(submit this one to gitHub for credit on this assignment)</p>
<p>This is from CodingBat “count_evens” (<a class="reference external" href="http://codingbat.com/prob/p189616">http://codingbat.com/prob/p189616</a>)</p>
<p><em>Using a list comprehension</em>, return the number of even ints in the given array.</p>
<p>Note: the % “mod” operator computes the remainder, e.g. <tt class="docutils literal"><span class="pre">5</span> <span class="pre">%</span> <span class="pre">2</span></tt> is 1.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">count_evens</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">])</span> <span class="o">==</span> <span class="mi">3</span>
<span class="n">count_evens</span><span class="p">([</span><span class="mi">2</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">0</span><span class="p">])</span> <span class="o">==</span> <span class="mi">3</span>
<span class="n">count_evens</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">5</span><span class="p">])</span> <span class="o">==</span> <span class="mi">0</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">count_evens</span><span class="p">(</span><span class="n">nums</span><span class="p">):</span>
<span class="n">one_line_comprehension_here</span>
</pre></div>
</div>
</div>
<div class="section" id="dict-and-set-comprehensions">
<h3><tt class="docutils literal"><span class="pre">dict</span></tt> and <tt class="docutils literal"><span class="pre">set</span></tt> comprehensions<a class="headerlink" href="#dict-and-set-comprehensions" title="Permalink to this headline">¶</a></h3>
<p>Let’s revisiting the dict/set lab – see how much you can do with
comprehensions instead.</p>
<p>Specifically, look at these:</p>
<p>First a slightly bigger, more interesting (or at least bigger..) dict:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">food_prefs</span> <span class="o">=</span> <span class="p">{</span><span class="s">"name"</span><span class="p">:</span> <span class="s">u"Chris"</span><span class="p">,</span>
<span class="s">u"city"</span><span class="p">:</span> <span class="s">u"Seattle"</span><span class="p">,</span>
<span class="s">u"cake"</span><span class="p">:</span> <span class="s">u"chocolate"</span><span class="p">,</span>
<span class="s">u"fruit"</span><span class="p">:</span> <span class="s">u"mango"</span><span class="p">,</span>
<span class="s">u"salad"</span><span class="p">:</span> <span class="s">u"greek"</span><span class="p">,</span>
<span class="s">u"pasta"</span><span class="p">:</span> <span class="s">u"lasagna"</span><span class="p">}</span>
</pre></div>
</div>
<p>1. Print the dict by passing it to a string format method, so that you
get something like:</p>
<blockquote>
<div><dl class="docutils">
<dt>“Chris is from Seattle, and he likes chocolate cake, mango fruit,</dt>
<dd>greek salad, and lasagna pasta”</dd>
</dl>
</div></blockquote>
<p>2. Using a list comprehension, build a dictionary of numbers from zero
to fifteen and the hexadecimal equivalent (string is fine).</p>
<ol class="arabic simple" start="3">
<li>Do the previous entirely with a dict comprehension – should be a one-liner</li>
</ol>
<p>4. Using the dictionary from item 1: Make a dictionary using the same
keys but with the number of ‘a’s in each value. You can do this either
by editing the dict in place, or making a new one. If you edit in place,
make a copy first!</p>
<p>5. Create sets s2, s3 and s4 that contain numbers from zero through twenty,
divisible 2, 3 and 4.</p>
<blockquote>
<div><ol class="loweralpha simple">
<li>Do this with one set comprehension for each set.</li>
<li>What if you had a lot more than 3? – Don’t Repeat Yourself (DRY)<ul>
<li>create a sequence that holds all three sets</li>
<li>loop through that sequence to build the sets up – so no repeated code.</li>
</ul>
</li>
<li>Extra credit: do it all as a one-liner by nesting a set comprehension inside a list comprehension. (OK, that may be getting carried away!)</li>
</ol>
</div></blockquote>
</div>
<div class="section" id="lambda-and-keyword-argument-magic">
<h3>lambda and keyword argument magic<a class="headerlink" href="#lambda-and-keyword-argument-magic" title="Permalink to this headline">¶</a></h3>
<p>Write a function that returns a list of n functions,
such that each one, when called, will return the input value,
incremented by an increasing number.</p>
<p>Use a for loop, <tt class="docutils literal"><span class="pre">lambda</span></tt>, and a keyword argument</p>
<p>( Extra credit ):</p>
<p>Do it with a list comprehension, instead of a for loop</p>
<p>Not clear? here’s what you should get</p>
<div class="highlight-ipython"><div class="highlight"><pre><span class="gp">In [96]: </span><span class="n">the_list</span> <span class="o">=</span> <span class="n">function_builder</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="go">### so the_list should contain n functions (callables)</span>
<span class="gp">In [97]: </span><span class="n">the_list</span><span class="p">[</span><span class="mi">0</span><span class="p">](</span><span class="mi">2</span><span class="p">)</span>
<span class="gh">Out[97]: </span><span class="go">2</span>
<span class="go">## the zeroth element of the list is a function that add 0</span>
<span class="go">## to the input, hence called with 2, returns 2</span>
<span class="gp">In [98]: </span><span class="n">the_list</span><span class="p">[</span><span class="mi">1</span><span class="p">](</span><span class="mi">2</span><span class="p">)</span>
<span class="gh">Out[98]: </span><span class="go">3</span>
<span class="go">## the 1st element of the list is a function that adds 1</span>
<span class="go">## to the input value, thus called with 2, returns 3</span>
<span class="gp">In [100]: </span><span class="k">for</span> <span class="n">f</span> <span class="ow">in</span> <span class="n">the_list</span><span class="p">:</span>
<span class="go"> print f(5)</span>
<span class="gp"> .....:</span>
<span class="go">5</span>
<span class="go">6</span>
<span class="go">7</span>
<span class="go">8</span>
<span class="go">### If you loop through them all, and call them, each one adds one more</span>
<span class="go">to the input, 5... i.e. the nth function in the list adds n to the input.</span>
</pre></div>
</div>
</div>
<div class="section" id="functional-files">
<h3>Functional files<a class="headerlink" href="#functional-files" title="Permalink to this headline">¶</a></h3>
<p>Write a program that takes a filename and “cleans” the file be removing all the leading and trailing whitespace from each line.</p>
<p>Read in the original file and write out a new one, either creating a new file or overwriting the existing one.</p>
<p>Give your user the option of which to perform.</p>
<p>Use <tt class="docutils literal"><span class="pre">map()</span></tt> to do the work.</p>
<p>Write a second version using a comprehension.</p>
<p><tt class="docutils literal"><span class="pre">sys.argv</span></tt> hold the command line arguments the user typed in. If the user types:</p>
<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span>python the_script a_file_name
</pre></div>
</div>
<p>Then:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">sys</span>
<span class="n">filename</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
</pre></div>
</div>
<p>will get <tt class="docutils literal"><span class="pre">filename</span> <span class="pre">==</span> <span class="pre">"a_file_name"</span></tt></p>
</div>
<div class="section" id="recommended-reading">
<h3>Recommended Reading<a class="headerlink" href="#recommended-reading" title="Permalink to this headline">¶</a></h3>
<ul class="simple">
<li>LPTHW: Ex 40 - 45</li>
</ul>
<p><a class="reference external" href="http://learnpythonthehardway.org/book/">http://learnpythonthehardway.org/book/</a></p>
<ul class="simple">
<li>Dive Into Python: chapter 4, 5</li>
</ul>
<p><a class="reference external" href="http://www.diveintopython.net/toc/index.html">http://www.diveintopython.net/toc/index.html</a></p>
</div>
</div>
</div>
</div>
<footer>
<div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
<a href="session06.html" class="btn btn-neutral float-right" title="Session Six: Object oriented programming: Classes, instances, attributes, and subclassing"/>Next <span class="fa fa-arrow-circle-right"></span></a>
<a href="session04.html" class="btn btn-neutral" title="Session Four: Dictionaries, Sets, Exceptions, and Files"><span class="fa fa-arrow-circle-left"></span> Previous</a>
</div>
<hr/>
<div role="contentinfo">
<p>
© Copyright 2014, Christopher Barker, Cris Ewing, .
</p>
</div>
<a href="https://github.com/snide/sphinx_rtd_theme">Sphinx theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>
</footer>
</div>
</div>
</section>
</div>
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT:'./',
VERSION:'1.3',
COLLAPSE_INDEX:false,
FILE_SUFFIX:'.html',
HAS_SOURCE: true
};
</script>
<script type="text/javascript" src="_static/jquery.js"></script>
<script type="text/javascript" src="_static/underscore.js"></script>
<script type="text/javascript" src="_static/doctools.js"></script>
<script type="text/javascript" src="_static/js/theme.js"></script>
<script type="text/javascript">
jQuery(function () {
SphinxRtdTheme.StickyNav.enable();
});
</script>
</body>
</html>