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<h1>Unicode In Python, Completely Demystified</h1>
</div>
</div>
<div class="presentation">
<div class="slide" id="slide0">
<h1 class="title">Unicode In Python, Completely Demystified</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>Kumar McMillan</td></tr>
<tr class="field"><th class="docinfo-name">Location:</th><td class="field-body">PyCon 2008, Chicago</td>
</tr>
<tr class="field"><th class="docinfo-name">URL:</th><td class="field-body"><a class="reference external" href="http://farmdev.com/talks/unicode/">http://farmdev.com/talks/unicode/</a></td>
</tr>
<tr class="field"><th class="docinfo-name">Source:</th><td class="field-body"><a class="reference external" href="https://github.com/kumar303/unicode-in-python">https://github.com/kumar303/unicode-in-python</a></td>
</tr>
</tbody>
</table>
</div>
<div class="slide" id="what-does-this-mean">
<h1>What does this mean?</h1>
<pre class="literal-block">
UnicodeDecodeError: 'ascii' codec
can't decode byte 0xc4 in position
10: ordinal not in range(128)
</pre>
<ul class="incremental simple">
<li>Never seen this exception?</li>
<li>Seen it and sort of fixed it?</li>
<li>This is a confusing error</li>
</ul>
<ul class="handout simple">
<li>If you've never seen this before but want to write Python code, this talk is for you</li>
<li>If you've seen this before and have no idea how to solve it, this talk is for you</li>
<li>This is a really confusing error if you don't know what Python is trying to do for you; this talk aims to clarify</li>
</ul>
</div>
<div class="slide" id="overview">
<h1>Overview</h1>
<ul class="simple">
<li>The truth about strings in Python</li>
<li>The magic of Unicode</li>
<li>How to work with Unicode in Python 2<ul>
<li>fundamental concept</li>
<li>example code</li>
</ul>
</li>
<li>Glimpse at Unicode in Python 3</li>
<li>Ask lots of questions</li>
<li>Corrections?</li>
</ul>
</div>
<div class="slide" id="why-use-unicode-in-python">
<h1>Why use Unicode in Python?</h1>
<ul class="incremental simple">
<li>handle non-English languages</li>
<li>use 3rd party modules</li>
<li>accept arbitrary text input</li>
<li>you will love Unicode</li>
<li>you will hate Unicode</li>
</ul>
</div>
<div class="slide" id="web-application">
<h1>Web application</h1>
<img alt="images/text-lifecycle-web.png" src="images/text-lifecycle-web.png" />
<pre class="handout literal-block">
[form input] => [Python] => [HTML]
</pre>
<ul class="handout simple">
<li>accepts input as text</li>
<li>writes text to an html file</li>
</ul>
</div>
<div class="slide" id="interacting-with-a-database">
<h1>Interacting with a database</h1>
<img alt="images/text-lifecycle-db.png" src="images/text-lifecycle-db.png" />
<pre class="handout literal-block">
[read from DB] => [Python] => [write to DB]
</pre>
<ul class="handout simple">
<li>accepts input as text</li>
<li>writes text to the database</li>
</ul>
</div>
<div class="slide" id="command-line-script">
<h1>Command line script</h1>
<img alt="images/text-lifecycle-script.png" src="images/text-lifecycle-script.png" />
<pre class="handout literal-block">
[text files] => [Python] => [stdout]
</pre>
<ul class="handout simple">
<li>accepts input as text</li>
<li>writes text to stdout or other files</li>
</ul>
</div>
<div class="slide" id="let-s-open-a-utf-8-file">
<h1>Let's open a UTF-8 file</h1>
<div class="section" id="ivan-krstic">
<h2>Ivan Krstić</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> f <span style="color: #666666">=</span> <span style="color: #008000">open</span>(<span style="color: #BA2121">'/tmp/ivan_utf8.txt'</span>, <span style="color: #BA2121">'r'</span>)
<span style="color: #666666">>>></span> ivan_utf8 <span style="color: #666666">=</span> f<span style="color: #666666">.</span>read()
<span style="color: #666666">>>></span> ivan_utf8
<span style="color: #BA2121">'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\xc4\x87</span><span style="color: #BA2121">'</span>
</pre></div>
<ul class="handout simple">
<li>Ivan Krstić is the director of security architecture at OLPC</li>
<li>pretend you opened this in a desktop text editor (nothing fancy like vi)
and you saved it in UTF-8 format. This might not have been the default.</li>
<li>now you are opening the file in Python</li>
</ul>
</div>
</div>
<div class="slide" id="what-is-it">
<h1>What is it?</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_utf8
<span style="color: #BA2121">'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\xc4\x87</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> <span style="color: #008000">type</span>(ivan_utf8)
<span style="color: #666666"><</span><span style="color: #008000">type</span> <span style="color: #BA2121">'str'</span><span style="color: #666666">></span>
</pre></div>
<ul class="incremental simple">
<li>a string of bytes!</li>
<li>1 byte = 8 bits</li>
<li>A bit is either "0" or "1"</li>
</ul>
</div>
<div class="slide" id="text-is-encoded">
<h1>Text is encoded</h1>
<div class="section" id="id1">
<h2>Ivan Krstić</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #BA2121">'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\xc4\x87</span><span style="color: #BA2121">'</span>
</pre></div>
<ul class="incremental simple">
<li>This string is encoded in UTF-8 format</li>
<li>An encoding is a set of rules that assign numeric values to each text character</li>
<li>Notice the c with a hachek takes up 2 bytes</li>
<li>Other encodings might represent ć differently</li>
<li>Python stdlib supports over 100 encodings</li>
</ul>
<ul class="handout simple">
<li>c with a hachek is part of the Croatian language</li>
<li>each encoding has its own byte representation of text</li>
</ul>
</div>
</div>
<div class="slide" id="ascii">
<h1>ASCII</h1>
<table border="1" class="docutils">
<colgroup>
<col width="35%" />
<col width="16%" />
<col width="16%" />
<col width="16%" />
<col width="16%" />
</colgroup>
<tbody valign="top">
<tr><td><strong>char</strong></td>
<td>I</td>
<td>v</td>
<td>a</td>
<td>n</td>
</tr>
<tr><td><strong>hex</strong></td>
<td>\x49</td>
<td>\x76</td>
<td>\x61</td>
<td>\x6e</td>
</tr>
<tr><td><strong>decimal</strong></td>
<td>73</td>
<td>118</td>
<td>97</td>
<td>110</td>
</tr>
</tbody>
</table>
<ul class="incremental simple">
<li>UTF-8 is an extension of ASCII</li>
<li>created in 1963 as the <strong>American</strong> Standard Code for Information Interchange</li>
<li>each character is 1 byte</li>
<li>128 possible characters</li>
</ul>
</div>
<div class="slide" id="id2">
<h1>ASCII</h1>
<table border="1" class="docutils">
<colgroup>
<col width="27%" />
<col width="12%" />
<col width="12%" />
<col width="12%" />
<col width="12%" />
<col width="12%" />
<col width="12%" />
</colgroup>
<tbody valign="top">
<tr><td><strong>char</strong></td>
<td>K</td>
<td>r</td>
<td>s</td>
<td>t</td>
<td>i</td>
<td>ć</td>
</tr>
<tr><td><strong>hex</strong></td>
<td>\x4b</td>
<td>\x76</td>
<td>\x72</td>
<td>\x74</td>
<td>\x69</td>
<td>nope</td>
</tr>
<tr><td><strong>decimal</strong></td>
<td>75</td>
<td>118</td>
<td>114</td>
<td>116</td>
<td>105</td>
<td>sorry</td>
</tr>
</tbody>
</table>
<ul class="incremental simple">
<li>ć cannot be encoded as ASCII</li>
<li>d'oh!</li>
</ul>
</div>
<div class="slide" id="built-in-string-types">
<h1>built-in string types</h1>
<p>(Python 2)</p>
<pre class="literal-block">
<type 'basestring'>
|
+--<type 'str'>
|
+--<type 'unicode'>
</pre>
</div>
<div class="slide" id="important-methods">
<h1>Important methods</h1>
<div class="section" id="s-decode-encoding">
<h2>s.decode(<em>encoding</em>)</h2>
<ul class="simple">
<li><tt class="docutils literal"><type 'str'></tt> to <tt class="docutils literal"><type 'unicode'></tt></li>
</ul>
</div>
<div class="section" id="u-encode-encoding">
<h2>u.encode(<em>encoding</em>)</h2>
<ul class="simple">
<li><tt class="docutils literal"><type 'unicode'></tt> to <tt class="docutils literal"><type 'str'></tt></li>
</ul>
</div>
</div>
<div class="slide" id="the-problem">
<h1>The problem</h1>
<p>Can't my Python text remain encoded?</p>
<div class="section" id="id3">
<h2>Ivan Krstić</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_utf8
<span style="color: #BA2121">'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\xc4\x87</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> <span style="color: #008000">len</span>(ivan_utf8)
<span style="color: #666666">12</span>
<span style="color: #666666">>>></span> ivan_utf8[<span style="color: #666666">-1</span>]
<span style="color: #BA2121">'</span><span style="color: #BB6622; font-weight: bold">\x87</span><span style="color: #BA2121">'</span>
</pre></div>
<ul class="handout simple">
<li>isn't encoded text good enough? No decoding errors anywhere</li>
<li>is the length of Ivan Krstić really 12?<ul>
<li>what happens if the text were encoded differently?</li>
</ul>
</li>
<li>is the last character really hexadecimal 87? Is that what I wanted?</li>
</ul>
</div>
</div>
<div class="slide" id="unicode-is-more-accurate">
<h1>Unicode is more accurate</h1>
<div class="section" id="id4">
<h2>Ivan Krstić</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_utf8
<span style="color: #BA2121">'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\xc4\x87</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> ivan_uni <span style="color: #666666">=</span> ivan_utf8<span style="color: #666666">.</span>decode(<span style="color: #BA2121">'utf-8'</span>)
<span style="color: #666666">>>></span> ivan_uni
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> <span style="color: #008000">type</span>(ivan_uni)
<span style="color: #666666"><</span><span style="color: #008000">type</span> <span style="color: #BA2121">'unicode'</span><span style="color: #666666">></span>
</pre></div>
</div>
</div>
<div class="slide" id="id5">
<h1>Unicode is more accurate</h1>
<div class="section" id="id6">
<h2>Ivan Krstić</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_uni
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> <span style="color: #008000">len</span>(ivan_uni)
<span style="color: #666666">11</span>
<span style="color: #666666">>>></span> ivan_uni[<span style="color: #666666">-1</span>]
<span style="color: #BA2121">u'</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
</pre></div>
</div>
</div>
<div class="slide" id="unicode-what-is-it">
<h1>Unicode, what is it?</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
</pre></div>
<ul class="incremental simple">
<li>a way to represent text without bytes</li>
<li>unique number (code point) for each character of every language</li>
<li>supports all major languages written today</li>
<li>defines over 1 million code points</li>
</ul>
<ul class="handout simple">
<li>supports...<ul>
<li>European alphabets</li>
<li>Middle Eastern right-to-left</li>
<li>scripts of Asia</li>
<li>technical math symbols</li>
<li>et cetera</li>
</ul>
</li>
</ul>
</div>
<div class="slide" id="unicode-the-ideal">
<h1>Unicode, the ideal</h1>
<p>If ASCII, UTF-8, and other byte strings are "text" ...</p>
<p class="incremental big">...then Unicode is "text-ness";</p>
<p class="incremental huge">it is the abstract form of text</p>
<ul class="handout simple">
<li><a class="reference external" href="http://en.wikipedia.org/wiki/Platonic_idealism">http://en.wikipedia.org/wiki/Platonic_idealism</a></li>
</ul>
</div>
<div class="slide" id="unicode-is-a-concept">
<h1>Unicode is a concept</h1>
<table border="1" class="docutils">
<colgroup>
<col width="31%" />
<col width="69%" />
</colgroup>
<tbody valign="top">
<tr><td><strong>letter</strong></td>
<td><strong>Unicode Code Point</strong></td>
</tr>
<tr><td>ć</td>
<td>\u0107</td>
</tr>
</tbody>
</table>
<ul class="simple">
<li>to save Unicode to disk you have to encode it</li>
</ul>
<table border="1" class="docutils">
<colgroup>
<col width="23%" />
<col width="25%" />
<col width="23%" />
<col width="30%" />
</colgroup>
<tbody valign="top">
<tr><td colspan="4">Byte Encodings</td>
</tr>
<tr><td><strong>letter</strong></td>
<td><strong>UTF-8</strong></td>
<td><strong>UTF-16</strong></td>
<td><strong>Shift-JIS</strong></td>
</tr>
<tr><td>ć</td>
<td>\xc4\x87</td>
<td>\x07\x01</td>
<td>\x85\xc9</td>
</tr>
</tbody>
</table>
</div>
<div class="slide" id="unicode-transformation-format">
<h1>Unicode Transformation Format</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ab <span style="color: #666666">=</span> <span style="color: #008000">unicode</span>(<span style="color: #BA2121">'AB'</span>)
</pre></div>
<div class="section" id="utf-8">
<h2>UTF-8</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ab<span style="color: #666666">.</span>encode(<span style="color: #BA2121">'utf-8'</span>)
<span style="color: #BA2121">'AB'</span>
</pre></div>
<ul class="incremental simple">
<li>variable byte representation</li>
<li>first 128 characters encoded just like ASCII</li>
<li>1 byte (8 bits) to 4 bytes per code point</li>
</ul>
</div>
</div>
<div class="slide" id="id7">
<h1>Unicode Transformation Format</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ab <span style="color: #666666">=</span> <span style="color: #008000">unicode</span>(<span style="color: #BA2121">'AB'</span>)
</pre></div>
<div class="section" id="utf-16">
<h2>UTF-16</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ab<span style="color: #666666">.</span>encode(<span style="color: #BA2121">'utf-16'</span>)
<span style="color: #BA2121">'</span><span style="color: #BB6622; font-weight: bold">\xff\xfe</span><span style="color: #BA2121">A</span><span style="color: #BB6622; font-weight: bold">\x00</span><span style="color: #BA2121">B</span><span style="color: #BB6622; font-weight: bold">\x00</span><span style="color: #BA2121">'</span>
</pre></div>
<ul class="incremental simple">
<li>variable byte representation</li>
<li>2 bytes (16 bits) to 4 bytes per code point</li>
<li>optimized for languages residing in the 2 byte character range</li>
</ul>
</div>
</div>
<div class="slide" id="id8">
<h1>Unicode Transformation Format</h1>
<div class="section" id="utf-32">
<h2>UTF-32</h2>
<ul class="incremental simple">
<li>fixed width byte representation, fastest</li>
<li>4 bytes (32 bits) per code point</li>
<li>not supported in Python</li>
</ul>
</div>
</div>
<div class="slide" id="unicode-chart">
<h1>Unicode chart</h1>
<div class="section" id="ian-albert-s-unicode-chart">
<h2>Ian Albert's Unicode chart</h2>
<ul class="incremental simple">
<li>this guy decided to print the entire Unicode chart</li>
<li>1,114,112 code points</li>
<li>6 feet by 12 feet</li>
<li>22,017 × 42,807 pixels</li>
</ul>
</div>
</div>
<div class="slide" id="id9">
<h1>Unicode chart</h1>
<img alt="images/unichart-printed.jpg" src="images/unichart-printed.jpg" />
<p class="handout">Ian Albert's Unicode chart. Says it only cost him $20 at Kinko's but he was pretty sure they rang him up wrong.</p>
</div>
<div class="slide" id="unicode-chart-50">
<h1>Unicode chart 50 %</h1>
<img alt="images/unichart-50.jpg" src="images/unichart-50.jpg" />
</div>
<div class="slide" id="unicode-chart-100">
<h1>Unicode chart 100 %</h1>
<img alt="images/unichart-100.jpg" src="images/unichart-100.jpg" />
</div>
<div class="slide" id="decoding-text-into-unicode">
<h1>Decoding text into Unicode</h1>
<ul class="incremental simple">
<li>It's mostly automatic</li>
<li>this happens a lot in 3rd party modules</li>
<li>Python will try to decode it for you</li>
</ul>
</div>
<div class="slide" id="python-magic">
<h1>Python magic</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_uni
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> f <span style="color: #666666">=</span> <span style="color: #008000">open</span>(<span style="color: #BA2121">'/tmp/ivan.txt'</span>, <span style="color: #BA2121">'w'</span>)
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>write(ivan_uni)
Traceback (most recent call last):
<span style="color: #666666">...</span>
<span style="color: #D2413A; font-weight: bold">UnicodeEncodeError</span>: <span style="color: #BA2121">'ascii'</span> codec can<span style="color: #BA2121">'t encode character u'</span>\u0107<span style="color: #BA2121">' in position 10: ordinal not in range(128)</span>
</pre></div>
</div>
<div class="slide" id="python-magic-revealed">
<h1>Python magic, revealed</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_uni
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> f <span style="color: #666666">=</span> <span style="color: #008000">open</span>(<span style="color: #BA2121">'/tmp/ivan.txt'</span>, <span style="color: #BA2121">'w'</span>)
<span style="color: #666666">>>></span> <span style="color: #008000; font-weight: bold">import</span> <span style="color: #0000FF; font-weight: bold">sys</span>
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>write(ivan_uni<span style="color: #666666">.</span>encode(
<span style="color: #666666">...</span> sys<span style="color: #666666">.</span>getdefaultencoding()))
<span style="color: #666666">...</span>
Traceback (most recent call last):
<span style="color: #666666">...</span>
<span style="color: #D2413A; font-weight: bold">UnicodeEncodeError</span>: <span style="color: #BA2121">'ascii'</span> codec can<span style="color: #BA2121">'t encode character u'</span>\u0107<span style="color: #BA2121">' in position 10: ordinal not in range(128)</span>
</pre></div>
</div>
<div class="slide" id="gasp">
<h1>Gasp!</h1>
<p class="center huge">THE DEFAULT
ENCODING FOR
PYTHON 2
IS ASCII</p>
</div>
<div class="slide" id="just-reset-it">
<h1>Just reset it?!</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%">sys<span style="color: #666666">.</span>setdefaultencoding(<span style="color: #BA2121">'utf-8'</span>)
</pre></div>
<ul class="incremental simple">
<li>can't I just put this in <tt class="docutils literal">sitecustomize.py</tt>?</li>
<li>No!</li>
<li>your code will not work on other Python installations</li>
<li>more trouble than it's worth</li>
</ul>
</div>
<div class="slide" id="solution">
<h1>Solution</h1>
<ol class="incremental big arabic simple">
<li><strong>Decode</strong> early</li>
<li><strong>Unicode</strong> everywhere</li>
<li><strong>Encode</strong> late</li>
</ol>
</div>
<div class="slide" id="decode-early">
<h1>1. Decode early</h1>
<p>Decode to <tt class="docutils literal"><type 'unicode'></tt> ASAP</p>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> <span style="color: #008000; font-weight: bold">def</span> <span style="color: #0000FF">to_unicode_or_bust</span>(
<span style="color: #666666">...</span> obj, encoding<span style="color: #666666">=</span><span style="color: #BA2121">'utf-8'</span>):
<span style="color: #666666">...</span> <span style="color: #008000; font-weight: bold">if</span> <span style="color: #008000">isinstance</span>(obj, <span style="color: #008000">basestring</span>):
<span style="color: #666666">...</span> <span style="color: #008000; font-weight: bold">if</span> <span style="color: #AA22FF; font-weight: bold">not</span> <span style="color: #008000">isinstance</span>(obj, <span style="color: #008000">unicode</span>):
<span style="color: #666666">...</span> obj <span style="color: #666666">=</span> <span style="color: #008000">unicode</span>(obj, encoding)
<span style="color: #666666">...</span> <span style="color: #008000; font-weight: bold">return</span> obj
<span style="color: #666666">...</span>
<span style="color: #666666">>>></span>
</pre></div>
<p class="handout">detects if object is a string and if so converts to unicode, if not already.</p>
</div>
<div class="slide" id="unicode-everywhere">
<h1>2. Unicode everywhere</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> to_unicode_or_bust(ivan_uni)
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> to_unicode_or_bust(ivan_utf8)
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> to_unicode_or_bust(<span style="color: #666666">1234</span>)
<span style="color: #666666">1234</span>
</pre></div>
</div>
<div class="slide" id="encode-late">
<h1>3. Encode late</h1>
<p>Encode to <tt class="docutils literal"><type 'str'></tt> when you write to disk or <strong>print</strong></p>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> f <span style="color: #666666">=</span> <span style="color: #008000">open</span>(<span style="color: #BA2121">'/tmp/ivan_out.txt'</span>,<span style="color: #BA2121">'wb'</span>)
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>write(ivan_uni<span style="color: #666666">.</span>encode(<span style="color: #BA2121">'utf-8'</span>))
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>close()
</pre></div>
</div>
<div class="slide" id="shortcuts">
<h1>Shortcuts</h1>
<div class="section" id="codecs-open">
<h2>codecs.open()</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> <span style="color: #008000; font-weight: bold">import</span> <span style="color: #0000FF; font-weight: bold">codecs</span>
<span style="color: #666666">>>></span> f <span style="color: #666666">=</span> codecs<span style="color: #666666">.</span>open(<span style="color: #BA2121">'/tmp/ivan_utf8.txt'</span>, <span style="color: #BA2121">'r'</span>,
<span style="color: #666666">...</span> encoding<span style="color: #666666">=</span><span style="color: #BA2121">'utf-8'</span>)
<span style="color: #666666">...</span>
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>read()
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>close()
</pre></div>
</div>
</div>
<div class="slide" id="id10">
<h1>Shortcuts</h1>
<div class="section" id="id11">
<h2>codecs.open()</h2>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> <span style="color: #008000; font-weight: bold">import</span> <span style="color: #0000FF; font-weight: bold">codecs</span>
<span style="color: #666666">>>></span> f <span style="color: #666666">=</span> codecs<span style="color: #666666">.</span>open(<span style="color: #BA2121">'/tmp/ivan_utf8.txt'</span>, <span style="color: #BA2121">'w'</span>,
<span style="color: #666666">...</span> encoding<span style="color: #666666">=</span><span style="color: #BA2121">'utf-8'</span>)
<span style="color: #666666">...</span>
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>write(ivan_uni)
<span style="color: #666666">>>></span> f<span style="color: #666666">.</span>close()
</pre></div>
</div>
</div>
<div class="slide" id="python-2-unicode-incompatibility">
<h1>Python 2 Unicode incompatibility</h1>
<ul class="simple">
<li>some 3rd party modules incompatible<ul>
<li>submit bugs!</li>
</ul>
</li>
<li>some builtin modules are incompatible<ul>
<li>csv</li>
</ul>
</li>
</ul>
</div>
<div class="slide" id="python-2-unicode-workarounds">
<h1>Python 2 Unicode workarounds</h1>
<ul class="simple">
<li>momentarily encode as UTF-8, then decode immediately</li>
<li>csv documentation shows you how to do this</li>
</ul>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> ivan_bytes <span style="color: #666666">=</span> ivan_uni<span style="color: #666666">.</span>encode(<span style="color: #BA2121">'utf-8'</span>)
<span style="color: #666666">>>></span> <span style="color: #408080; font-style: italic"># do stuff</span>
<span style="color: #666666">>>></span> ivan_bytes<span style="color: #666666">.</span>decode(<span style="color: #BA2121">'utf-8'</span>)
<span style="color: #BA2121">u'Ivan Krsti</span><span style="color: #BB6622; font-weight: bold">\u0107</span><span style="color: #BA2121">'</span>
</pre></div>
</div>
<div class="slide" id="the-bom">
<h1>The BOM</h1>
<ul class="incremental simple">
<li>sometimes at beginning of files</li>
<li>Byte Order Mark</li>
<li>essential for UTF-16, UTF-32 files<ul>
<li>Big Endian (MSB first)</li>
<li>Little Endian (LSB first)</li>
</ul>
</li>
<li>UTF-8 BOM just says "I am UTF-8"<ul>
<li>popular in Windows</li>
</ul>
</li>
</ul>
</div>
<div class="slide" id="detecting-the-bom">
<h1>Detecting the BOM</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> f <span style="color: #666666">=</span> <span style="color: #008000">open</span>(<span style="color: #BA2121">'/tmp/ivan_utf16.txt'</span>,<span style="color: #BA2121">'r'</span>)
<span style="color: #666666">>>></span> sample <span style="color: #666666">=</span> f<span style="color: #666666">.</span>read(<span style="color: #666666">4</span>)
<span style="color: #666666">>>></span> sample
<span style="color: #BA2121">'</span><span style="color: #BB6622; font-weight: bold">\xff\xfe</span><span style="color: #BA2121">I</span><span style="color: #BB6622; font-weight: bold">\x00</span><span style="color: #BA2121">'</span>
</pre></div>
<ul class="simple">
<li>BOM can be 2, 3, or 4 bytes long</li>
</ul>
</div>
<div class="slide" id="id12">
<h1>Detecting the BOM</h1>
<div class="highlight" style="background: #f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">>>></span> <span style="color: #008000; font-weight: bold">import</span> <span style="color: #0000FF; font-weight: bold">codecs</span>
<span style="color: #666666">>>></span> (sample<span style="color: #666666">.</span>startswith(codecs<span style="color: #666666">.</span>BOM_UTF16_LE) <span style="color: #AA22FF; font-weight: bold">or</span>
<span style="color: #666666">...</span> sample<span style="color: #666666">.</span>startswith(codecs<span style="color: #666666">.</span>BOM_UTF16_BE))
<span style="color: #666666">...</span>
<span style="color: #008000">True</span>
<span style="color: #666666">>>></span> sample<span style="color: #666666">.</span>startswith(codecs<span style="color: #666666">.</span>BOM_UTF8)
<span style="color: #008000">False</span>
</pre></div>
</div>
<div class="slide" id="do-i-have-to-remove-the-bom">
<h1>Do I have to remove the BOM?</h1>
<ul class="incremental simple">
<li>maybe</li>
<li>decoding UTF-16 removes the BOM automatically</li>
<li>but not UTF-8<ul>
<li><em>unless</em> you say <tt class="docutils literal"><span class="pre">s.decode('utf-8-sig')</span></tt><ul>
<li>available since Python 2.5</li>