{{ message }}
-
Notifications
You must be signed in to change notification settings - Fork 62
Expand file tree
/
Copy pathportable_code.html
More file actions
281 lines (258 loc) · 16.8 KB
/
Copy pathportable_code.html
File metadata and controls
281 lines (258 loc) · 16.8 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
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Developer’s tips for writing code for Python 2 and 3 — Matplotlib 2.2.0 documentation</title>
<link rel="stylesheet" href="../_static/mpl.css"
type="text/css" />
<link rel="stylesheet" href="../_static/pygments.css"
type="text/css" />
<link rel="stylesheet" href="../_static/gallery.css" type="text/css" />
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: '../',
VERSION: '2.2.0',
COLLAPSE_INDEX: false,
FILE_SUFFIX: '.html',
HAS_SOURCE: true,
SOURCELINK_SUFFIX: '.txt'
};
</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>
<link rel="search" type="application/opensearchdescription+xml"
title="Search within Matplotlib 2.2.0 documentation"
href="../_static/opensearch.xml"/>
<link rel="shortcut icon" href="../_static/favicon.ico"/>
<link rel="index" title="Index" href="../genindex.html"
/>
<link rel="search" title="Search" href="../search.html"
/>
<link rel="top" title="Matplotlib 2.2.0 documentation" href="../index.html" />
<link rel="up" title="The Matplotlib Developers’ Guide" href="index.html" />
<link rel="next" title="Working with Matplotlib source code" href="gitwash/index.html" />
<link rel="prev" title="Developer’s guide for creating scales and transformations" href="add_new_projection.html" />
<link rel="canonical" href="https://matplotlib.org/2.2.5/devel/portable_code.html" />
<script data-domain="matplotlib.org" defer="defer" src="https://views.scientific-python.org/js/script.js"></script>
</head>
<body>
<div id="unreleased-message"> You are reading an old version of the documentation (v2.2.0). For the latest version see <a href="/stable/">https://matplotlib.org/stable/</a> </div>
<div style="background-color: white; text-align: left; padding: 10px 10px 15px 15px; position: relative;">
<a href="../index.html">
<div style="float: left; position: absolute; width: 496px; bottom: 0; padding-bottom: 24px"><span style="float: right; color: #789; background: white">Version 2.2.0</span></div>
<img src="../_static/logo2.png" height="125px" border="0" alt="matplotlib"/></a>
<!-- The "Fork me on github" ribbon -->
<div id="forkongithub"><a href="https://github.com/matplotlib/matplotlib">Fork me on GitHub</a></div>
</div>
<div class="related">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="gitwash/index.html" title="Working with Matplotlib source code"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="add_new_projection.html" title="Developer’s guide for creating scales and transformations"
accesskey="P">previous</a> |</li>
<li><a href="../index.html">home</a>| </li>
<li><a href="../gallery/index.html">examples</a>| </li>
<li><a href="../tutorials/index.html">tutorials</a>| </li>
<li><a href="../api/pyplot_summary.html">pyplot</a>| </li>
<li><a href="../contents.html">docs</a> »</li>
<li><a href="index.html" accesskey="U">The Matplotlib Developers’ Guide</a> »</li>
</ul>
</div>
<div class="sphinxsidebar">
<div class="sphinxsidebarwrapper">
<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Developer’s tips for writing code for Python 2 and 3</a><ul>
<li><a class="reference internal" href="#welcome-to-the-future">Welcome to the <code class="docutils literal notranslate"><span class="pre">__future__</span></code></a></li>
<li><a class="reference internal" href="#finding-places-to-use-six">Finding places to use six</a></li>
<li><a class="reference internal" href="#the-dreaded-u-escapes">The dreaded <code class="docutils literal notranslate"><span class="pre">\u</span></code> escapes</a></li>
<li><a class="reference internal" href="#iteration">Iteration</a></li>
<li><a class="reference internal" href="#numpy-specific-things">Numpy-specific things</a></li>
</ul>
</li>
</ul>
<div class="relations">
<h3>Related Topics</h3>
<ul>
<li><a href="../contents.html">Documentation overview</a><ul>
<li><a href="index.html">The Matplotlib Developers’ Guide</a><ul>
<li>Previous: <a href="add_new_projection.html" title="previous chapter">Developer’s guide for creating scales and transformations</a></li>
<li>Next: <a href="gitwash/index.html" title="next chapter">Working with <em>Matplotlib</em> source code</a></li>
</ul></li>
</ul></li>
</ul>
</div>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../_sources/devel/portable_code.rst.txt"
rel="nofollow">Show Source</a></li>
</ul>
</div>
<div id="searchbox" style="display: none" role="search">
<h3>Quick search</h3>
<div class="searchformwrapper">
<form class="search" action="../search.html" method="get">
<input type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
</div>
<script type="text/javascript">$('#searchbox').show(0);</script>
</div>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body">
<div class="section" id="developer-s-tips-for-writing-code-for-python-2-and-3">
<span id="portable-code"></span><h1>Developer’s tips for writing code for Python 2 and 3<a class="headerlink" href="#developer-s-tips-for-writing-code-for-python-2-and-3" title="Permalink to this headline">¶</a></h1>
<p>As of matplotlib 1.4, the <a class="reference external" href="http://pythonhosted.org/six/">six</a>
library is used to support Python 2 and 3 from a single code base.
The <code class="xref py py-obj docutils literal notranslate"><span class="pre">2to3</span></code> tool is no longer used.</p>
<p>This document describes some of the issues with that approach and some
recommended solutions. It is not a complete guide to Python 2 and 3
compatibility.</p>
<div class="section" id="welcome-to-the-future">
<h2>Welcome to the <code class="docutils literal notranslate"><span class="pre">__future__</span></code><a class="headerlink" href="#welcome-to-the-future" title="Permalink to this headline">¶</a></h2>
<p>The top of every <code class="xref py py-obj docutils literal notranslate"><span class="pre">py</span></code> file should include the following:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">__future__</span> <span class="k">import</span> <span class="p">(</span><span class="n">absolute_import</span><span class="p">,</span> <span class="n">division</span><span class="p">,</span>
<span class="n">print_function</span><span class="p">,</span> <span class="n">unicode_literals</span><span class="p">)</span>
<span class="kn">import</span> <span class="nn">six</span>
</pre></div>
</div>
<p>This will make the Python 2 interpreter behave as close to Python 3 as
possible.</p>
<p>All matplotlib files should also import <code class="xref py py-obj docutils literal notranslate"><span class="pre">six</span></code>, whether they are using
it or not, just to make moving code between modules easier, as <code class="xref py py-obj docutils literal notranslate"><span class="pre">six</span></code>
gets used <em>a lot</em>.</p>
</div>
<div class="section" id="finding-places-to-use-six">
<h2>Finding places to use six<a class="headerlink" href="#finding-places-to-use-six" title="Permalink to this headline">¶</a></h2>
<p>The only way to make sure code works on both Python 2 and 3 is to make sure it
is covered by unit tests.</p>
<p>However, the <code class="xref py py-obj docutils literal notranslate"><span class="pre">2to3</span></code> commandline tool can also be used to locate places
that require special handling with <code class="xref py py-obj docutils literal notranslate"><span class="pre">six</span></code>.</p>
<p>(The <a class="reference external" href="https://pypi.python.org/pypi/modernize">modernize</a> tool may
also be handy, though I’ve never used it personally).</p>
<p>The <a class="reference external" href="http://pythonhosted.org/six/">six</a> documentation serves as a
good reference for the sorts of things that need to be updated.</p>
</div>
<div class="section" id="the-dreaded-u-escapes">
<h2>The dreaded <code class="docutils literal notranslate"><span class="pre">\u</span></code> escapes<a class="headerlink" href="#the-dreaded-u-escapes" title="Permalink to this headline">¶</a></h2>
<p>When <code class="xref py py-obj docutils literal notranslate"><span class="pre">from</span> <span class="pre">__future__</span> <span class="pre">import</span> <span class="pre">unicode_literals</span></code> is used, all string
literals (not preceded with a <code class="xref py py-obj docutils literal notranslate"><span class="pre">b</span></code>) will become unicode literals.</p>
<p>Normally, one would use “raw” string literals to encode strings that
contain a lot of slashes that we don’t want Python to interpret as
special characters. A common example in matplotlib is when it deals
with TeX and has to represent things like <code class="docutils literal notranslate"><span class="pre">r"\usepackage{foo}"</span></code>.
Unfortunately, on Python 2there is no way to represent <code class="xref py py-obj docutils literal notranslate"><span class="pre">u</span></code> in a raw
unicode string literal, since it will always be interpreted as the
start of a unicode character escape, such as <code class="xref py py-obj docutils literal notranslate"><span class="pre">u20af</span></code>. The only
solution is to use a regular (non-raw) string literal and repeat all
slashes, e.g. <code class="docutils literal notranslate"><span class="pre">"\\usepackage{foo}"</span></code>.</p>
<p>The following shows the problem on Python 2:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="sa">ur</span><span class="s1">'\u'</span>
File <span class="nb">"<stdin>"</span>, line <span class="m">1</span>
<span class="gr">SyntaxError</span>: <span class="n">(unicode error) 'rawunicodeescape' codec can't decode bytes in</span>
<span class="go">position 0-1: truncated \uXXXX</span>
<span class="gp">>>> </span><span class="sa">ur</span><span class="s1">'</span><span class="se">\\</span><span class="s1">u'</span>
<span class="go">u'\\\\u'</span>
<span class="gp">>>> </span><span class="sa">u</span><span class="s1">'\u'</span>
File <span class="nb">"<stdin>"</span>, line <span class="m">1</span>
<span class="gr">SyntaxError</span>: <span class="n">(unicode error) 'unicodeescape' codec can't decode bytes in</span>
<span class="go">position 0-1: truncated \uXXXX escape</span>
<span class="gp">>>> </span><span class="sa">u</span><span class="s1">'</span><span class="se">\\</span><span class="s1">u'</span>
<span class="go">u'\\u'</span>
</pre></div>
</div>
<p>This bug has been fixed in Python 3, however, we can’t take advantage
of that and still support Python 2:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="sa">r</span><span class="s1">'\u'</span>
<span class="go">'\\u'</span>
<span class="gp">>>> </span><span class="sa">r</span><span class="s1">'</span><span class="se">\\</span><span class="s1">u'</span>
<span class="go">'\\\\u'</span>
<span class="gp">>>> </span><span class="s1">'\u'</span>
File <span class="nb">"<stdin>"</span>, line <span class="m">1</span>
<span class="gr">SyntaxError</span>: <span class="n">(unicode error) 'unicodeescape' codec can't decode bytes in</span>
<span class="go">position 0-1: truncated \uXXXX escape</span>
<span class="gp">>>> </span><span class="s1">'</span><span class="se">\\</span><span class="s1">u'</span>
<span class="go">'\\u'</span>
</pre></div>
</div>
</div>
<div class="section" id="iteration">
<h2>Iteration<a class="headerlink" href="#iteration" title="Permalink to this headline">¶</a></h2>
<p>The behavior of the methods for iterating over the items, values and
keys of a dictionary has changed in Python 3. Additionally, other
built-in functions such as <a class="reference external" href="https://docs.python.org/3/library/functions.html#zip" title="(in Python v3.6)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">zip</span></code></a>, <a class="reference external" href="https://docs.python.org/3/library/stdtypes.html#range" title="(in Python v3.6)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">range</span></code></a> and <a class="reference external" href="https://docs.python.org/3/library/functions.html#map" title="(in Python v3.6)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">map</span></code></a> have changed to
return iterators rather than temporary lists.</p>
<p>In many cases, the performance implications of iterating vs. creating
a temporary list won’t matter, so it’s tempting to use the form that
is simplest to read. However, that results in code that behaves
differently on Python 2 and 3, leading to subtle bugs that may not be
detected by the regression tests. Therefore, unless the loop in
question is provably simple and doesn’t call into other code, the
<code class="xref py py-obj docutils literal notranslate"><span class="pre">six</span></code> versions that ensure the same behavior on both Python 2 and 3
should be used. The following table shows the mapping of equivalent
semantics between Python 2, 3 and six for <code class="xref py py-obj docutils literal notranslate"><span class="pre">dict.items()</span></code>:</p>
<table border="1" class="docutils">
<colgroup>
<col width="33%" />
<col width="33%" />
<col width="33%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Python 2</th>
<th class="head">Python 3</th>
<th class="head">six</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">d.items()</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">list(d.items())</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">list(six.iteritems(d))</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">d.iteritems()</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">d.items()</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">six.iteritems(d)</span></code></td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="numpy-specific-things">
<h2>Numpy-specific things<a class="headerlink" href="#numpy-specific-things" title="Permalink to this headline">¶</a></h2>
<p>When specifying dtypes, all strings must be byte strings on Python 2
and unicode strings on Python 3. The best way to handle this is to
force cast them using <code class="xref py py-obj docutils literal notranslate"><span class="pre">str()</span></code>. The same is true of structure
specifiers in the <a class="reference external" href="https://docs.python.org/3/library/struct.html#module-struct" title="(in Python v3.6)"><code class="xref py py-obj docutils literal notranslate"><span class="pre">struct</span></code></a> built-in module.</p>
</div>
</div>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="footer">
© Copyright 2002 - 2012 John Hunter, Darren Dale, Eric Firing, Michael Droettboom and the Matplotlib development team; 2012 - 2017 The Matplotlib development team.
Last updated on Mar 06, 2018.
Created using <a
href="http://sphinx-doc.org/">Sphinx</a> 1.7.1.
</div>
</body>
<footer>
</footer>
</html>
You can’t perform that action at this time.