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
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st February 2003), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>
Indexing Support
</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%"
summary="header">
<tr>
<td valign="top" width="300">
<h3>
<a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../boost.png" border=
"0"></a>
</h3>
</td>
<td valign="top">
<h1 align="center">
<a href="../index.html">Boost.Python</a>
</h1>
<h2> Headers <boost/python/indexing/indexing_suite.hpp><br>
<boost/python/indexing/vector_indexing_suite.hpp></h2>
</td>
</tr>
</table>
<hr>
<h2>
Contents
</h2>
<dl class="page-index">
<dt>
<a href="#introduction">Introduction</a>
</dt>
<dt>
<a href="#interface">Interface</a>
</dt>
<dd>
<dl class="page-index">
<dt>
<a href="#indexing_suite">indexing_suite</a>
</dt>
<dt>
<a href="#indexing_suite_subclasses">indexing_suite
sub-classes</a>
</dt>
<dd>
<dl class="page-index">
<dt>
<a href="#vector_indexing_suite">vector_indexing_suite</a>
</dt>
</dl>
</dd>
</dl>
</dd>
</dl>
<dl>
<dt>
<a href="#indexing_suite_class">indexing_suite class</a>
</dt>
<dt>
<a href="#vector_indexing_suite_class">vector_indexing_suite
class<br>
</a><a href="#map_indexing_suite_class">map_indexing_suite class</a> </dt>
</dl>
<hr>
<h2>
<a name="introduction" id="introduction"></a>Introduction
</h2>
<p>
Indexing is a Boost Python facility for easy exportation of indexable
C++ containers to Python. Indexable containers are containers that
allow random access through the operator[] (e.g. std::vector).
</p>
<p>
While Boost Python has all the facilities needed to expose indexable
C++ containers such as the ubiquitous std::vector to Python, the
procedure is not as straightforward as we'd like it to be. Python
containers do not map easily to C++ containers. Emulating Python
containers in C++ (see Python Reference Manual, <a href=
"http://www.python.org/doc/current/ref/sequence-types.html">Emulating
container types</a>) using Boost Python is non trivial. There are a lot
of issues to consider before we can map a C++ container to Python.
These involve implementing wrapper functions for the methods
<strong>__len__</strong>, <strong>__getitem__</strong>,
<strong>__setitem__</strong>, <strong>__delitem__,</strong>
<strong>__iter__</strong> and <strong>__contains</strong>.
</p>
<p>
The goals:
</p>
<ul>
<li>
<div>
Make indexable C++ containers behave exactly as one would expect a
Python container to behave.
</div>
</li>
<li>
Provide default reference semantics for container element indexing
(<tt>__getitem__</tt>) such that <tt>c[i]</tt> can be mutable.
Require:
<div>
<pre>
val = c[i]
c[i].m()
val == c[i]
</pre>
</div>where <tt>m</tt> is a non-const (mutating) member function
(method).
</li>
<li>
Return safe references from <tt>__getitem__</tt> such that subsequent
adds and deletes to and from the container will not result in
dangling references (will not crash Python).
</li>
<li>
Support slice indexes.
</li>
<li>
Accept Python container arguments (e.g. lists, tuples) wherever
appropriate.
</li>
<li>
Allow for extensibility through re-definable policy classes.
</li>
<li>
Provide predefined support for the most common STL and STL like
indexable containers.
</li>
</ul>
<hr>
<h2> <a name="interface"></a>The Boost.Python Indexing Interface</h2>
<h3> <a name="indexing_suite"></a>indexing_suite [ Header <boost/python/indexing/indexing_suite.hpp>
]</h3>
<p>
The <tt>indexing_suite</tt> class is the base class for the
management of C++ containers intended to be integrated to Python. The
objective is make a C++ container look and feel and behave exactly as
we'd expect a Python container. The class automatically wraps these
special Python methods (taken from the Python reference: <a href=
"http://www.python.org/doc/current/ref/sequence-types.html">Emulating
container types</a>):
</p>
<dl>
<dd>
<dl>
<dt>
<b><a name="l2h-126"><tt class=
"method">__len__</tt></a></b>(<var>self</var>)
</dt>
<dd>
Called to implement the built-in function <tt class=
"function">len()</tt><a name="l2h-134"> </a> Should return
the length of the object, an integer <code>>=</code> 0. Also,
an object that doesn't define a <tt class=
"method">__nonzero__()</tt> method and whose <tt class=
"method">__len__()</tt> method returns zero is considered to be
false in a Boolean context. <a name="l2h-128"> </a>
</dd>
</dl>
<dl>
<dt>
<b><a name="l2h-129"><tt class=
"method">__getitem__</tt></a></b>(<var>self, key</var>)
</dt>
<dd>
Called to implement evaluation of
<code><var>self</var>[<var>key</var>]</code>. For sequence types,
the accepted keys should be integers and slice
objects.<a name="l2h-135"> </a> Note that the special
interpretation of negative indexes (if the class wishes to
emulate a sequence type) is up to the <tt class=
"method">__getitem__()</tt> method. If <var>key</var> is of
an inappropriate type, <tt class="exception">TypeError</tt>
may be raised; if of a value outside the set of indexes for
the sequence (after any special interpretation of negative
values), <tt class="exception">IndexError</tt> should be
raised. <span class="note"><b class="label">Note:</b>
<tt class="keyword">for</tt> loops expect that an <tt class=
"exception">IndexError</tt> will be raised for illegal
indexes to allow proper detection of the end of the
sequence.</span>
</dd>
</dl>
<dl>
<dt>
<b><a name="l2h-130"><tt class=
"method">__setitem__</tt></a></b>(<var>self, key, value</var>)
</dt>
<dd>
Called to implement assignment to
<code><var>self</var>[<var>key</var>]</code>. Same note as for
<tt class="method">__getitem__()</tt>. This should only be
implemented for mappings if the objects support changes to the
values for keys, or if new keys can be added, or for sequences if
elements can be replaced. The same exceptions should be raised
for improper <var>key</var> values as for the <tt class=
"method">__getitem__()</tt> method.
</dd>
</dl>
<dl>
<dt>
<b><a name="l2h-131"><tt class=
"method">__delitem__</tt></a></b>(<var>self, key</var>)
</dt>
<dd>
Called to implement deletion of
<code><var>self</var>[<var>key</var>]</code>. Same note as for
<tt class="method">__getitem__()</tt>. This should only be
implemented for mappings if the objects support removal of keys,
or for sequences if elements can be removed from the sequence.
The same exceptions should be raised for improper <var>key</var>
values as for the <tt class="method">__getitem__()</tt> method.
</dd>
</dl>
<dl>
<dt>
<b><a name="l2h-132"><tt class=
"method">__iter__</tt></a></b>(<var>self</var>)
</dt>
<dd>
This method is called when an iterator is required for a
container. This method should return a new iterator object that
can iterate over all the objects in the container. For mappings,
it should iterate over the keys of the container, and should also
be made available as the method <tt class=
"method">iterkeys()</tt>.
<p>
Iterator objects also need to implement this method; they are
required to return themselves. For more information on iterator
objects, see ``<a class="ulink" href=
"http://www.python.org/doc/current/lib/typeiter.html">Iterator
Types</a>'' in the <em class="citetitle"><a href=
"http://www.python.org/doc/current/lib/lib.html" title=
"Python Library Reference">Python Library Reference</a></em>.
</p>
</dd>
</dl>
<dl>
<dt>
<b><a name="l2h-133"><tt class=
"method">__contains__</tt></a></b>(<var>self, item</var>)
</dt>
<dd>
Called to implement membership test operators. Should return true
if <var>item</var> is in <var>self</var>, false otherwise. For
mapping objects, this should consider the keys of the mapping
rather than the values or the key-item pairs.
</dd>
</dl>
</dd>
</dl>
<h3> <a name="indexing_suite_subclasses"></a>indexing_suite sub-classes</h3>
<p>
The <tt>indexing_suite</tt> is not meant to be used as is. A couple of
policy functions must be supplied by subclasses of
<tt>indexing_suite</tt>. However, a set of <tt>indexing_suite</tt>
subclasses for the standard indexable STL containers will be provided,
In most cases, we can simply use the available predefined suites. In
some cases, we can refine the predefined suites to suit our needs.
</p>
<h3> <a name="vector_indexing_suite"></a>vector_indexing_suite [ Header <boost/python/indexing/vector_indexing_suite.hpp>
] </h3>
<p>
The <tt>vector_indexing_suite</tt> class is a predefined
<tt>indexing_suite</tt> derived class designed to wrap
<tt>std::vector</tt> (and <tt>std::vector</tt> like [i.e. a class with
std::vector interface]) classes. It provides all the policies required by the
<tt>indexing_suite</tt>.
</p>
<p>
Example usage:
</p>
<pre>
class X {...};
...
class_<std::vector<X> >("XVec")
.def(vector_indexing_suite<std::vector<X> >())
;
</pre>
<p>
<tt>XVec</tt> is now a full-fledged Python container (see the
<a href="../../test/vector_indexing_suite.cpp">example in full</a>,
along with its <a href="../../test/vector_indexing_suite.py">python
test</a>).
</p>
<h3><a name="map_indexing_suite" id="map_indexing_suite"></a>map_indexing_suite [ Header <boost/python/indexing/map_indexing_suite.hpp> ] </h3>
<p> The <tt>map_indexing_suite</tt> class is a predefined <tt>indexing_suite</tt> derived class designed to wrap <tt>std::map</tt> (and <tt>std::map</tt> like [i.e. a class with std::map interface]) classes. It provides all the policies required by the <tt>indexing_suite</tt>. </p>
<p> Example usage: </p>
<pre>
class X {...};
...
class_<std::map<X> >("XMap")
.def(map_indexing_suite<std::map<X> >())
;
</pre>
<p> By default indexed elements are returned by proxy. This can be disabled by supplying <tt>true</tt> in the NoProxy template parameter. <tt>XMap</tt> is now a full-fledged Python container (see the <a href="../../test/map_indexing_suite.cpp">example in full</a>, along with its <a href="../../test/map_indexing_suite.py">python test</a>).</p>
<hr>
<h2>
<a name="indexing_suite_class"></a>indexing_suite class </h2>
<h2> <tt>indexing_suite<<br>
</tt><tt>class Container<br>
, class DerivedPolicies<font color="#007F00"><br>
</font></tt> <tt>,
bool NoProxy<br>
,
bool NoSlice<br>
</tt><tt>, class Data<br>
, class Index<br>
</tt><tt>, class Key</tt></h2>
<table width="100%" border="1">
<tr>
<td>
<strong>Template Parameter</strong><br>
</td>
<td>
<strong>Requirements</strong>
</td>
<td>
<strong>Semantics</strong>
</td>
<td>
<strong>Default</strong>
</td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>Container</tt></font>
</td>
<td>
A class type
</td>
<td>
The container type to be wrapped to Python.
</td>
<td>
</td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>DerivedPolicies</tt></font>
</td>
<td>
A subclass of indexing_suite
</td>
<td>
Derived classes provide the policy hooks. See <a href=
"#DerivedPolicies">DerivedPolicies</a> below.
</td>
<td>
</td>
</tr>
<tr>
<td> <font color="#007F00"><tt>NoProxy</tt></font> </td>
<td> A boolean </td>
<td> By default indexed elements have Python reference semantics and are returned by proxy. This can be disabled by supplying <strong>true</strong> in the <tt>NoProxy</tt> template parameter. </td>
<td> false </td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>NoSlice</tt></font>
</td>
<td>
A boolean
</td>
<td>
Do not allow slicing. </td>
<td>
false
</td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>Data</tt></font>
</td>
<td>
</td>
<td>
The container's data type.
</td>
<td>
<tt>Container::value_type</tt>
</td>
</tr>
<tr>
<td> <font color="#007F00"><tt>Index</tt></font> </td>
<td> </td>
<td> The container's index type. </td>
<td> <tt>Container::size_type</tt> </td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>Key</tt></font>
</td>
<td>
</td>
<td>
The container's key type.
</td>
<td>
<tt>Container::value_type</tt>
</td>
</tr>
</table>
<pre>
template <<br> class Container
, class DerivedPolicies
, bool NoProxy = false<br> , bool NoSlice = false
, class Data = typename Container::value_type
, class Index = typename Container::size_type
, class Key = typename Container::value_type
><br> class indexing_suite
: unspecified
{
public:
indexing_suite(); // default constructor
}
</pre>
<h2>
<tt><a name="DerivedPolicies"></a>DerivedPolicies</tt>
</h2>
<dl>
<dd>
Derived classes provide the hooks needed by
the <tt>indexing_suite:</tt>
</dd>
</dl>
<pre> data_type&
get_item(Container& container, index_type i);
static object
get_slice(Container& container, index_type from, index_type to);
static void
set_item(Container& container, index_type i, data_type const& v);
static void
set_slice(
Container& container, index_type from,
index_type to, data_type const& v
);
template <class Iter>
static void<br> set_slice(Container& container, index_type from,
index_type to, Iter first, Iter last
);
static void
delete_item(Container& container, index_type i);
static void
delete_slice(Container& container, index_type from, index_type to);
static size_t
size(Container& container);
template <class T>
static bool
contains(Container& container, T const& val);
static index_type
convert_index(Container& container, PyObject* i);
static index_type
adjust_index(index_type current, index_type from,
index_type to, size_type len
);
</pre>
<blockquote>
<p>
Most of these policies are self explanatory. <tt>However,
<strong>convert_index</strong></tt> and
<tt><strong>adjust_index</strong></tt> deserve some explanation.
</p>
<p>
<strong><tt>convert_index</tt></strong> converts a Python index into
a C++ index that the container can handle. For instance, negative
indexes in Python, by convention, start counting from the right(e.g.
<tt>C[-1]</tt> indexes the rightmost element in <tt>C</tt>).
<strong><tt>convert_index</tt></strong> should handle the necessary
conversion for the C++ container (e.g. convert <tt>-1</tt> to
<tt>C.size()-1</tt>). <tt><strong>convert_index</strong></tt> should
also be able to convert the type of the index (A dynamic Python type)
to the actual type that the C++ container expects.
</p>
<p>
When a container expands or contracts, held indexes to its elements
must be adjusted to follow the movement of data. For instance, if we
erase 3 elements, starting from index 0 from a 5 element vector, what
used to be at index 4 will now be at index 1:
</p>
<pre>
[a][b][c][d][e] ---> [d][e]
^ ^
4 1
</pre>
<p>
<strong><tt>adjust_index</tt></strong> takes care of the adjustment.
Given a current index, the function should return the adjusted index
when data in the container at index <tt>from</tt>..<tt>to</tt> is
replaced by <tt>len</tt> elements.
</p>
</blockquote>
<div>
<hr>
<h2>
<a name="vector_indexing_suite_class"></a>vector_indexing_suite class
</h2>
<h3>
Class template <tt><br>
vector_indexing_suite<<br>
class <font color="#007F00">Container</font><br>
, bool <font color="#007F00">NoProxy</font><br>
, class <font color="#007F00">DerivedPolicies</font>></tt>
</h3>
<table width="100%" border="1">
<tr>
<td>
<strong>Template Parameter</strong><br>
</td>
<td>
<strong>Requirements</strong>
</td>
<td>
<strong>Semantics</strong>
</td>
<td>
<strong>Default</strong>
</td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>Container</tt></font>
</td>
<td>
A class type
</td>
<td>
The container type to be wrapped to Python.
</td>
<td>
</td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>NoProxy</tt></font>
</td>
<td>
A boolean
</td>
<td>
By default indexed elements have Python reference semantics and
are returned by proxy. This can be disabled by supplying
<strong>true</strong> in the <tt>NoProxy</tt> template parameter.
</td>
<td>
false
</td>
</tr>
<tr>
<td>
<font color="#007F00"><tt>DerivedPolicies</tt></font>
</td>
<td>
A subclass of indexing_suite
</td>
<td>
The <tt>vector_indexing_suite</tt> may still be derived to
further tweak any of the predefined policies. Static polymorphism
through CRTP (James Coplien. "Curiously Recurring Template
Pattern". C++ Report, Feb. 1995) enables the base
<tt>indexing_suite</tt> class to call policy function of the most
derived class
</td>
<td>
</td>
</tr>
</table>
<pre>
template <<br> class Container,<br> bool NoProxy = false,<br> class DerivedPolicies = unspecified_default<br> class vector_indexing_suite : unspecified_base<br> {<br> public:<br><br> typedef typename Container::value_type data_type;<br> typedef typename Container::value_type key_type;<br> typedef typename Container::size_type index_type;<br> typedef typename Container::size_type size_type;<br> typedef typename Container::difference_type difference_type;<br> <br> data_type&<br> get_item(Container& container, index_type i);
static object
get_slice(Container& container, index_type from, index_type to);
static void<br> set_item(Container& container, index_type i, data_type const& v);
static void
set_slice(Container& container, index_type from,
index_type to, data_type const& v);
template <class Iter><br> static void<br> set_slice(Container& container, index_type from,<br> index_type to, Iter first, Iter last);
static void
delete_item(Container& container, index_type i);
static void
delete_slice(Container& container, index_type from, index_type to);<br>
static size_t
size(Container& container);
static bool
contains(Container& container, key_type const& key);
static index_type
convert_index(Container& container, PyObject* i);
static index_type
adjust_index(index_type current, index_type from,
index_type to, size_type len);
};
</pre>
<h2><a name="vector_indexing_suite_class"></a>map_indexing_suite class </h2>
<h3> Class template <tt><br>
map_indexing_suite<<br>
class <font color="#007F00">Container</font><br>
, bool <font color="#007F00">NoProxy</font><br>
, class <font color="#007F00">DerivedPolicies</font>></tt> </h3>
<table width="100%" border="1">
<tr>
<td> <strong>Template Parameter</strong><br>
</td>
<td> <strong>Requirements</strong> </td>
<td> <strong>Semantics</strong> </td>
<td> <strong>Default</strong> </td>
</tr>
<tr>
<td> <font color="#007F00"><tt>Container</tt></font> </td>
<td> A class type </td>
<td> The container type to be wrapped to Python. </td>
<td> </td>
</tr>
<tr>
<td> <font color="#007F00"><tt>NoProxy</tt></font> </td>
<td> A boolean </td>
<td> By default indexed elements have Python reference semantics and are returned by proxy. This can be disabled by supplying <strong>true</strong> in the <tt>NoProxy</tt> template parameter. </td>
<td> false </td>
</tr>
<tr>
<td> <font color="#007F00"><tt>DerivedPolicies</tt></font> </td>
<td> A subclass of indexing_suite </td>
<td> The <tt>vector_indexing_suite</tt> may still be derived to further tweak any of the predefined policies. Static polymorphism through CRTP (James Coplien. "Curiously Recurring Template Pattern". C++ Report, Feb. 1995) enables the base <tt>indexing_suite</tt> class to call policy function of the most derived class </td>
<td> </td>
</tr>
</table>
<pre>
template <<br> class Container,<br> bool NoProxy = false,<br> class DerivedPolicies = unspecified_default<br> class map_indexing_suite : unspecified_base<br> {<br> public:<br><br> typedef typename Container::value_type value_type;<br> typedef typename Container::value_type::second_type data_type;<br> typedef typename Container::key_type key_type;<br> typedef typename Container::key_type index_type;<br> typedef typename Container::size_type size_type;<br> typedef typename Container::difference_type difference_type;<br><br> static data_type&<br> get_item(Container& container, index_type i);
static void<br> set_item(Container& container, index_type i, data_type const& v);
static void
delete_item(Container& container, index_type i);<br>
static size_t
size(Container& container);
static bool
contains(Container& container, key_type const& key);
static bool<br> compare_index(Container& container, index_type a, index_type b);
<br> static index_type
convert_index(Container& container, PyObject* i);
};
</pre>
<hr>
© Copyright Joel de Guzman 2003. Permission to copy, use, modify,
sell and distribute this document is granted provided this copyright
notice appears in all copies. This document is provided "as is" without
express or implied warranty, and with no claim as to its suitability
for any purpose.
</div>
</body>
</html>
|
