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  198.   <section id="what-s-new-in-python-3-1">

  199. <h1>What’s New In Python 3.1<a class="headerlink" href="#what-s-new-in-python-3-1" title="Link to this heading">¶</a></h1>

  200. <dl class="field-list simple">

  201. <dt class="field-odd">Author<span class="colon">:</span></dt>

  202. <dd class="field-odd"><p>Raymond Hettinger</p>

  203. </dd>

  204. </dl>

  205. <p>This article explains the new features in Python 3.1, compared to 3.0.

  206. Python 3.1 was released on June 27, 2009.</p>

  207. <section id="pep-372-ordered-dictionaries">

  208. <h2>PEP 372: Ordered Dictionaries<a class="headerlink" href="#pep-372-ordered-dictionaries" title="Link to this heading">¶</a></h2>

  209. <p>Regular Python dictionaries iterate over key/value pairs in arbitrary order.

  210. Over the years, a number of authors have written alternative implementations

  211. that remember the order that the keys were originally inserted.  Based on

  212. the experiences from those implementations, a new

  213. <a class="reference internal" href="../library/collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.OrderedDict</span></code></a> class has been introduced.</p>

  214. <p>The OrderedDict API is substantially the same as regular dictionaries

  215. but will iterate over keys and values in a guaranteed order depending on

  216. when a key was first inserted.  If a new entry overwrites an existing entry,

  217. the original insertion position is left unchanged.  Deleting an entry and

  218. reinserting it will move it to the end.</p>

  219. <p>The standard library now supports use of ordered dictionaries in several

  220. modules.  The <a class="reference internal" href="../library/configparser.html#module-configparser" title="configparser: Configuration file parser."><code class="xref py py-mod docutils literal notranslate"><span class="pre">configparser</span></code></a> module uses them by default.  This lets

  221. configuration files be read, modified, and then written back in their original

  222. order.  The <em>_asdict()</em> method for <a class="reference internal" href="../library/collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-func docutils literal notranslate"><span class="pre">collections.namedtuple()</span></code></a> now

  223. returns an ordered dictionary with the values appearing in the same order as

  224. the underlying tuple indices.  The <a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> module is being built-out with

  225. an <em>object_pairs_hook</em> to allow OrderedDicts to be built by the decoder.

  226. Support was also added for third-party tools like <a class="reference external" href="https://pyyaml.org/">PyYAML</a>.</p>

  227. <div class="admonition seealso">

  228. <p class="admonition-title">See also</p>

  229. <dl class="simple">

  230. <dt><span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0372/"><strong>PEP 372</strong></a> - Ordered Dictionaries</dt><dd><p>PEP written by Armin Ronacher and Raymond Hettinger.  Implementation

  231. written by Raymond Hettinger.</p>

  232. </dd>

  233. </dl>

  234. </div>

  235. <p>Since an ordered dictionary remembers its insertion order, it can be used

  236. in conjunction with sorting to make a sorted dictionary:</p>

  237. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="c1"># regular unsorted dictionary</span>

  238. <span class="gp">&gt;&gt;&gt; </span><span class="n">d</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;banana&#39;</span><span class="p">:</span> <span class="mi">3</span><span class="p">,</span> <span class="s1">&#39;apple&#39;</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span> <span class="s1">&#39;pear&#39;</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span> <span class="s1">&#39;orange&#39;</span><span class="p">:</span> <span class="mi">2</span><span class="p">}</span>

  239. 

  240. <span class="gp">&gt;&gt;&gt; </span><span class="c1"># dictionary sorted by key</span>

  241. <span class="gp">&gt;&gt;&gt; </span><span class="n">OrderedDict</span><span class="p">(</span><span class="nb">sorted</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">(),</span> <span class="n">key</span><span class="o">=</span><span class="k">lambda</span> <span class="n">t</span><span class="p">:</span> <span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">]))</span>

  242. <span class="go">OrderedDict([(&#39;apple&#39;, 4), (&#39;banana&#39;, 3), (&#39;orange&#39;, 2), (&#39;pear&#39;, 1)])</span>

  243. 

  244. <span class="gp">&gt;&gt;&gt; </span><span class="c1"># dictionary sorted by value</span>

  245. <span class="gp">&gt;&gt;&gt; </span><span class="n">OrderedDict</span><span class="p">(</span><span class="nb">sorted</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">(),</span> <span class="n">key</span><span class="o">=</span><span class="k">lambda</span> <span class="n">t</span><span class="p">:</span> <span class="n">t</span><span class="p">[</span><span class="mi">1</span><span class="p">]))</span>

  246. <span class="go">OrderedDict([(&#39;pear&#39;, 1), (&#39;orange&#39;, 2), (&#39;banana&#39;, 3), (&#39;apple&#39;, 4)])</span>

  247. 

  248. <span class="gp">&gt;&gt;&gt; </span><span class="c1"># dictionary sorted by length of the key string</span>

  249. <span class="gp">&gt;&gt;&gt; </span><span class="n">OrderedDict</span><span class="p">(</span><span class="nb">sorted</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">(),</span> <span class="n">key</span><span class="o">=</span><span class="k">lambda</span> <span class="n">t</span><span class="p">:</span> <span class="nb">len</span><span class="p">(</span><span class="n">t</span><span class="p">[</span><span class="mi">0</span><span class="p">])))</span>

  250. <span class="go">OrderedDict([(&#39;pear&#39;, 1), (&#39;apple&#39;, 4), (&#39;orange&#39;, 2), (&#39;banana&#39;, 3)])</span>

  251. </pre></div>

  252. </div>

  253. <p>The new sorted dictionaries maintain their sort order when entries

  254. are deleted.  But when new keys are added, the keys are appended

  255. to the end and the sort is not maintained.</p>

  256. </section>

  257. <section id="pep-378-format-specifier-for-thousands-separator">

  258. <h2>PEP 378: Format Specifier for Thousands Separator<a class="headerlink" href="#pep-378-format-specifier-for-thousands-separator" title="Link to this heading">¶</a></h2>

  259. <p>The built-in <a class="reference internal" href="../library/functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code></a> function and the <a class="reference internal" href="../library/stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate"><span class="pre">str.format()</span></code></a> method use

  260. a mini-language that now includes a simple, non-locale aware way to format

  261. a number with a thousands separator.  That provides a way to humanize a

  262. program’s output, improving its professional appearance and readability:</p>

  263. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="nb">format</span><span class="p">(</span><span class="mi">1234567</span><span class="p">,</span> <span class="s1">&#39;,d&#39;</span><span class="p">)</span>

  264. <span class="go">&#39;1,234,567&#39;</span>

  265. <span class="gp">&gt;&gt;&gt; </span><span class="nb">format</span><span class="p">(</span><span class="mf">1234567.89</span><span class="p">,</span> <span class="s1">&#39;,.2f&#39;</span><span class="p">)</span>

  266. <span class="go">&#39;1,234,567.89&#39;</span>

  267. <span class="gp">&gt;&gt;&gt; </span><span class="nb">format</span><span class="p">(</span><span class="mf">12345.6</span> <span class="o">+</span> <span class="mf">8901234.12</span><span class="n">j</span><span class="p">,</span> <span class="s1">&#39;,f&#39;</span><span class="p">)</span>

  268. <span class="go">&#39;12,345.600000+8,901,234.120000j&#39;</span>

  269. <span class="gp">&gt;&gt;&gt; </span><span class="nb">format</span><span class="p">(</span><span class="n">Decimal</span><span class="p">(</span><span class="s1">&#39;1234567.89&#39;</span><span class="p">),</span> <span class="s1">&#39;,f&#39;</span><span class="p">)</span>

  270. <span class="go">&#39;1,234,567.89&#39;</span>

  271. </pre></div>

  272. </div>

  273. <p>The supported types are <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>, <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate"><span class="pre">complex</span></code></a>

  274. and <a class="reference internal" href="../library/decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate"><span class="pre">decimal.Decimal</span></code></a>.</p>

  275. <p>Discussions are underway about how to specify alternative separators

  276. like dots, spaces, apostrophes, or underscores.  Locale-aware applications

  277. should use the existing <em>n</em> format specifier which already has some support

  278. for thousands separators.</p>

  279. <div class="admonition seealso">

  280. <p class="admonition-title">See also</p>

  281. <dl class="simple">

  282. <dt><span class="target" id="index-1"></span><a class="pep reference external" href="https://peps.python.org/pep-0378/"><strong>PEP 378</strong></a> - Format Specifier for Thousands Separator</dt><dd><p>PEP written by Raymond Hettinger and implemented by Eric Smith and

  283. Mark Dickinson.</p>

  284. </dd>

  285. </dl>

  286. </div>

  287. </section>

  288. <section id="other-language-changes">

  289. <h2>Other Language Changes<a class="headerlink" href="#other-language-changes" title="Link to this heading">¶</a></h2>

  290. <p>Some smaller changes made to the core Python language are:</p>

  291. <ul>

  292. <li><p>Directories and zip archives containing a <code class="file docutils literal notranslate"><span class="pre">__main__.py</span></code>

  293. file can now be executed directly by passing their name to the

  294. interpreter. The directory/zipfile is automatically inserted as the

  295. first entry in sys.path.  (Suggestion and initial patch by Andy Chu;

  296. revised patch by Phillip J. Eby and Nick Coghlan; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=1739468">bpo-1739468</a>.)</p></li>

  297. <li><p>The <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate"><span class="pre">int()</span></code></a> type gained a <code class="docutils literal notranslate"><span class="pre">bit_length</span></code> method that returns the

  298. number of bits necessary to represent its argument in binary:</p>

  299. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">n</span> <span class="o">=</span> <span class="mi">37</span>

  300. <span class="gp">&gt;&gt;&gt; </span><span class="nb">bin</span><span class="p">(</span><span class="mi">37</span><span class="p">)</span>

  301. <span class="go">&#39;0b100101&#39;</span>

  302. <span class="gp">&gt;&gt;&gt; </span><span class="n">n</span><span class="o">.</span><span class="n">bit_length</span><span class="p">()</span>

  303. <span class="go">6</span>

  304. <span class="gp">&gt;&gt;&gt; </span><span class="n">n</span> <span class="o">=</span> <span class="mi">2</span><span class="o">**</span><span class="mi">123</span><span class="o">-</span><span class="mi">1</span>

  305. <span class="gp">&gt;&gt;&gt; </span><span class="n">n</span><span class="o">.</span><span class="n">bit_length</span><span class="p">()</span>

  306. <span class="go">123</span>

  307. <span class="gp">&gt;&gt;&gt; </span><span class="p">(</span><span class="n">n</span><span class="o">+</span><span class="mi">1</span><span class="p">)</span><span class="o">.</span><span class="n">bit_length</span><span class="p">()</span>

  308. <span class="go">124</span>

  309. </pre></div>

  310. </div>

  311. <p>(Contributed by Fredrik Johansson, Victor Stinner, Raymond Hettinger,

  312. and Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=3439">bpo-3439</a>.)</p>

  313. </li>

  314. <li><p>The fields in <a class="reference internal" href="../library/functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code></a> strings can now be automatically

  315. numbered:</p>

  316. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="s1">&#39;Sir </span><span class="si">{}</span><span class="s1"> of </span><span class="si">{}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="s1">&#39;Gallahad&#39;</span><span class="p">,</span> <span class="s1">&#39;Camelot&#39;</span><span class="p">)</span>

  317. <span class="go">&#39;Sir Gallahad of Camelot&#39;</span>

  318. </pre></div>

  319. </div>

  320. <p>Formerly, the string would have required numbered fields such as:

  321. <code class="docutils literal notranslate"><span class="pre">'Sir</span> <span class="pre">{0}</span> <span class="pre">of</span> <span class="pre">{1}'</span></code>.</p>

  322. <p>(Contributed by Eric Smith; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5237">bpo-5237</a>.)</p>

  323. </li>

  324. <li><p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">string.maketrans()</span></code> function is deprecated and is replaced by new

  325. static methods, <a class="reference internal" href="../library/stdtypes.html#bytes.maketrans" title="bytes.maketrans"><code class="xref py py-meth docutils literal notranslate"><span class="pre">bytes.maketrans()</span></code></a> and <a class="reference internal" href="../library/stdtypes.html#bytearray.maketrans" title="bytearray.maketrans"><code class="xref py py-meth docutils literal notranslate"><span class="pre">bytearray.maketrans()</span></code></a>.

  326. This change solves the confusion around which types were supported by the

  327. <a class="reference internal" href="../library/string.html#module-string" title="string: Common string operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">string</span></code></a> module. Now, <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>, <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>, and

  328. <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a> each have their own <strong>maketrans</strong> and <strong>translate</strong>

  329. methods with intermediate translation tables of the appropriate type.</p>

  330. <p>(Contributed by Georg Brandl; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5675">bpo-5675</a>.)</p>

  331. </li>

  332. <li><p>The syntax of the <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement now allows multiple context

  333. managers in a single statement:</p>

  334. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;mylog.txt&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">infile</span><span class="p">,</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;a.out&#39;</span><span class="p">,</span> <span class="s1">&#39;w&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">outfile</span><span class="p">:</span>

  335. <span class="gp">... </span>    <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">infile</span><span class="p">:</span>

  336. <span class="gp">... </span>        <span class="k">if</span> <span class="s1">&#39;&lt;critical&gt;&#39;</span> <span class="ow">in</span> <span class="n">line</span><span class="p">:</span>

  337. <span class="gp">... </span>            <span class="n">outfile</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">line</span><span class="p">)</span>

  338. </pre></div>

  339. </div>

  340. <p>With the new syntax, the <code class="xref py py-func docutils literal notranslate"><span class="pre">contextlib.nested()</span></code> function is no longer

  341. needed and is now deprecated.</p>

  342. <p>(Contributed by Georg Brandl and Mattias Brändström;

  343. <a class="reference external" href="https://codereview.appspot.com/53094">appspot issue 53094</a>.)</p>

  344. </li>

  345. <li><p><code class="docutils literal notranslate"><span class="pre">round(x,</span> <span class="pre">n)</span></code> now returns an integer if <em>x</em> is an integer.

  346. Previously it returned a float:</p>

  347. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="nb">round</span><span class="p">(</span><span class="mi">1123</span><span class="p">,</span> <span class="o">-</span><span class="mi">2</span><span class="p">)</span>

  348. <span class="go">1100</span>

  349. </pre></div>

  350. </div>

  351. <p>(Contributed by Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4707">bpo-4707</a>.)</p>

  352. </li>

  353. <li><p>Python now uses David Gay’s algorithm for finding the shortest floating

  354. point representation that doesn’t change its value.  This should help

  355. mitigate some of the confusion surrounding binary floating point

  356. numbers.</p>

  357. <p>The significance is easily seen with a number like <code class="docutils literal notranslate"><span class="pre">1.1</span></code> which does not

  358. have an exact equivalent in binary floating point.  Since there is no exact

  359. equivalent, an expression like <code class="docutils literal notranslate"><span class="pre">float('1.1')</span></code> evaluates to the nearest

  360. representable value which is <code class="docutils literal notranslate"><span class="pre">0x1.199999999999ap+0</span></code> in hex or

  361. <code class="docutils literal notranslate"><span class="pre">1.100000000000000088817841970012523233890533447265625</span></code> in decimal. That

  362. nearest value was and still is used in subsequent floating point

  363. calculations.</p>

  364. <p>What is new is how the number gets displayed.  Formerly, Python used a

  365. simple approach.  The value of <code class="docutils literal notranslate"><span class="pre">repr(1.1)</span></code> was computed as <code class="docutils literal notranslate"><span class="pre">format(1.1,</span>

  366. <span class="pre">'.17g')</span></code> which evaluated to <code class="docutils literal notranslate"><span class="pre">'1.1000000000000001'</span></code>. The advantage of

  367. using 17 digits was that it relied on IEEE-754 guarantees to assure that

  368. <code class="docutils literal notranslate"><span class="pre">eval(repr(1.1))</span></code> would round-trip exactly to its original value.  The

  369. disadvantage is that many people found the output to be confusing (mistaking

  370. intrinsic limitations of binary floating point representation as being a

  371. problem with Python itself).</p>

  372. <p>The new algorithm for <code class="docutils literal notranslate"><span class="pre">repr(1.1)</span></code> is smarter and returns <code class="docutils literal notranslate"><span class="pre">'1.1'</span></code>.

  373. Effectively, it searches all equivalent string representations (ones that

  374. get stored with the same underlying float value) and returns the shortest

  375. representation.</p>

  376. <p>The new algorithm tends to emit cleaner representations when possible, but

  377. it does not change the underlying values.  So, it is still the case that

  378. <code class="docutils literal notranslate"><span class="pre">1.1</span> <span class="pre">+</span> <span class="pre">2.2</span> <span class="pre">!=</span> <span class="pre">3.3</span></code> even though the representations may suggest otherwise.</p>

  379. <p>The new algorithm depends on certain features in the underlying floating

  380. point implementation.  If the required features are not found, the old

  381. algorithm will continue to be used.  Also, the text pickle protocols

  382. assure cross-platform portability by using the old algorithm.</p>

  383. <p>(Contributed by Eric Smith and Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=1580">bpo-1580</a>)</p>

  384. </li>

  385. </ul>

  386. </section>

  387. <section id="new-improved-and-deprecated-modules">

  388. <h2>New, Improved, and Deprecated Modules<a class="headerlink" href="#new-improved-and-deprecated-modules" title="Link to this heading">¶</a></h2>

  389. <ul>

  390. <li><p>Added a <a class="reference internal" href="../library/collections.html#collections.Counter" title="collections.Counter"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.Counter</span></code></a> class to support convenient

  391. counting of unique items in a sequence or iterable:</p>

  392. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">Counter</span><span class="p">([</span><span class="s1">&#39;red&#39;</span><span class="p">,</span> <span class="s1">&#39;blue&#39;</span><span class="p">,</span> <span class="s1">&#39;red&#39;</span><span class="p">,</span> <span class="s1">&#39;green&#39;</span><span class="p">,</span> <span class="s1">&#39;blue&#39;</span><span class="p">,</span> <span class="s1">&#39;blue&#39;</span><span class="p">])</span>

  393. <span class="go">Counter({&#39;blue&#39;: 3, &#39;red&#39;: 2, &#39;green&#39;: 1})</span>

  394. </pre></div>

  395. </div>

  396. <p>(Contributed by Raymond Hettinger; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=1696199">bpo-1696199</a>.)</p>

  397. </li>

  398. <li><p>Added a new module, <a class="reference internal" href="../library/tkinter.ttk.html#module-tkinter.ttk" title="tkinter.ttk: Tk themed widget set"><code class="xref py py-mod docutils literal notranslate"><span class="pre">tkinter.ttk</span></code></a> for access to the Tk themed widget set.

  399. The basic idea of ttk is to separate, to the extent possible, the code

  400. implementing a widget’s behavior from the code implementing its appearance.</p>

  401. <p>(Contributed by Guilherme Polo; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=2983">bpo-2983</a>.)</p>

  402. </li>

  403. <li><p>The <a class="reference internal" href="../library/gzip.html#gzip.GzipFile" title="gzip.GzipFile"><code class="xref py py-class docutils literal notranslate"><span class="pre">gzip.GzipFile</span></code></a> and <a class="reference internal" href="../library/bz2.html#bz2.BZ2File" title="bz2.BZ2File"><code class="xref py py-class docutils literal notranslate"><span class="pre">bz2.BZ2File</span></code></a> classes now support

  404. the context management protocol:</p>

  405. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="c1"># Automatically close file after writing</span>

  406. <span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">gzip</span><span class="o">.</span><span class="n">GzipFile</span><span class="p">(</span><span class="n">filename</span><span class="p">,</span> <span class="s2">&quot;wb&quot;</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>

  407. <span class="gp">... </span>    <span class="n">f</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;xxx&quot;</span><span class="p">)</span>

  408. </pre></div>

  409. </div>

  410. <p>(Contributed by Antoine Pitrou.)</p>

  411. </li>

  412. <li><p>The <a class="reference internal" href="../library/decimal.html#module-decimal" title="decimal: Implementation of the General Decimal Arithmetic  Specification."><code class="xref py py-mod docutils literal notranslate"><span class="pre">decimal</span></code></a> module now supports methods for creating a

  413. decimal object from a binary <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>.  The conversion is

  414. exact but can sometimes be surprising:</p>

  415. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">Decimal</span><span class="o">.</span><span class="n">from_float</span><span class="p">(</span><span class="mf">1.1</span><span class="p">)</span>

  416. <span class="go">Decimal(&#39;1.100000000000000088817841970012523233890533447265625&#39;)</span>

  417. </pre></div>

  418. </div>

  419. <p>The long decimal result shows the actual binary fraction being

  420. stored for <em>1.1</em>.  The fraction has many digits because <em>1.1</em> cannot

  421. be exactly represented in binary.</p>

  422. <p>(Contributed by Raymond Hettinger and Mark Dickinson.)</p>

  423. </li>

  424. <li><p>The <a class="reference internal" href="../library/itertools.html#module-itertools" title="itertools: Functions creating iterators for efficient looping."><code class="xref py py-mod docutils literal notranslate"><span class="pre">itertools</span></code></a> module grew two new functions.  The

  425. <a class="reference internal" href="../library/itertools.html#itertools.combinations_with_replacement" title="itertools.combinations_with_replacement"><code class="xref py py-func docutils literal notranslate"><span class="pre">itertools.combinations_with_replacement()</span></code></a> function is one of

  426. four for generating combinatorics including permutations and Cartesian

  427. products.  The <a class="reference internal" href="../library/itertools.html#itertools.compress" title="itertools.compress"><code class="xref py py-func docutils literal notranslate"><span class="pre">itertools.compress()</span></code></a> function mimics its namesake

  428. from APL.  Also, the existing <a class="reference internal" href="../library/itertools.html#itertools.count" title="itertools.count"><code class="xref py py-func docutils literal notranslate"><span class="pre">itertools.count()</span></code></a> function now has

  429. an optional <em>step</em> argument and can accept any type of counting

  430. sequence including <a class="reference internal" href="../library/fractions.html#fractions.Fraction" title="fractions.Fraction"><code class="xref py py-class docutils literal notranslate"><span class="pre">fractions.Fraction</span></code></a> and

  431. <a class="reference internal" href="../library/decimal.html#decimal.Decimal" title="decimal.Decimal"><code class="xref py py-class docutils literal notranslate"><span class="pre">decimal.Decimal</span></code></a>:</p>

  432. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="p">[</span><span class="n">p</span><span class="o">+</span><span class="n">q</span> <span class="k">for</span> <span class="n">p</span><span class="p">,</span><span class="n">q</span> <span class="ow">in</span> <span class="n">combinations_with_replacement</span><span class="p">(</span><span class="s1">&#39;LOVE&#39;</span><span class="p">,</span> <span class="mi">2</span><span class="p">)]</span>

  433. <span class="go">[&#39;LL&#39;, &#39;LO&#39;, &#39;LV&#39;, &#39;LE&#39;, &#39;OO&#39;, &#39;OV&#39;, &#39;OE&#39;, &#39;VV&#39;, &#39;VE&#39;, &#39;EE&#39;]</span>

  434. 

  435. <span class="gp">&gt;&gt;&gt; </span><span class="nb">list</span><span class="p">(</span><span class="n">compress</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">),</span> <span class="n">selectors</span><span class="o">=</span><span class="p">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">]))</span>

  436. <span class="go">[2, 3, 5, 7]</span>

  437. 

  438. <span class="gp">&gt;&gt;&gt; </span><span class="n">c</span> <span class="o">=</span> <span class="n">count</span><span class="p">(</span><span class="n">start</span><span class="o">=</span><span class="n">Fraction</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="n">step</span><span class="o">=</span><span class="n">Fraction</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">6</span><span class="p">))</span>

  439. <span class="gp">&gt;&gt;&gt; </span><span class="p">[</span><span class="nb">next</span><span class="p">(</span><span class="n">c</span><span class="p">),</span> <span class="nb">next</span><span class="p">(</span><span class="n">c</span><span class="p">),</span> <span class="nb">next</span><span class="p">(</span><span class="n">c</span><span class="p">),</span> <span class="nb">next</span><span class="p">(</span><span class="n">c</span><span class="p">)]</span>

  440. <span class="go">[Fraction(1, 2), Fraction(2, 3), Fraction(5, 6), Fraction(1, 1)]</span>

  441. </pre></div>

  442. </div>

  443. <p>(Contributed by Raymond Hettinger.)</p>

  444. </li>

  445. <li><p><a class="reference internal" href="../library/collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-func docutils literal notranslate"><span class="pre">collections.namedtuple()</span></code></a> now supports a keyword argument

  446. <em>rename</em> which lets invalid fieldnames be automatically converted to

  447. positional names in the form _0, _1, etc.  This is useful when

  448. the field names are being created by an external source such as a

  449. CSV header, SQL field list, or user input:</p>

  450. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">query</span> <span class="o">=</span> <span class="nb">input</span><span class="p">()</span>

  451. <span class="go">SELECT region, dept, count(*) FROM main GROUPBY region, dept</span>

  452. 

  453. <span class="gp">&gt;&gt;&gt; </span><span class="n">cursor</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="n">query</span><span class="p">)</span>

  454. <span class="gp">&gt;&gt;&gt; </span><span class="n">query_fields</span> <span class="o">=</span> <span class="p">[</span><span class="n">desc</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="k">for</span> <span class="n">desc</span> <span class="ow">in</span> <span class="n">cursor</span><span class="o">.</span><span class="n">description</span><span class="p">]</span>

  455. <span class="gp">&gt;&gt;&gt; </span><span class="n">UserQuery</span> <span class="o">=</span> <span class="n">namedtuple</span><span class="p">(</span><span class="s1">&#39;UserQuery&#39;</span><span class="p">,</span> <span class="n">query_fields</span><span class="p">,</span> <span class="n">rename</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>

  456. <span class="gp">&gt;&gt;&gt; </span><span class="n">pprint</span><span class="o">.</span><span class="n">pprint</span><span class="p">([</span><span class="n">UserQuery</span><span class="p">(</span><span class="o">*</span><span class="n">row</span><span class="p">)</span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">cursor</span><span class="p">])</span>

  457. <span class="go">[UserQuery(region=&#39;South&#39;, dept=&#39;Shipping&#39;, _2=185),</span>

  458. <span class="go"> UserQuery(region=&#39;North&#39;, dept=&#39;Accounting&#39;, _2=37),</span>

  459. <span class="go"> UserQuery(region=&#39;West&#39;, dept=&#39;Sales&#39;, _2=419)]</span>

  460. </pre></div>

  461. </div>

  462. <p>(Contributed by Raymond Hettinger; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=1818">bpo-1818</a>.)</p>

  463. </li>

  464. <li><p>The <a class="reference internal" href="../library/re.html#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.sub()</span></code></a>, <a class="reference internal" href="../library/re.html#re.subn" title="re.subn"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.subn()</span></code></a> and <a class="reference internal" href="../library/re.html#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.split()</span></code></a> functions now

  465. accept a flags parameter.</p>

  466. <p>(Contributed by Gregory Smith.)</p>

  467. </li>

  468. <li><p>The <a class="reference internal" href="../library/logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate"><span class="pre">logging</span></code></a> module now implements a simple <a class="reference internal" href="../library/logging.handlers.html#logging.NullHandler" title="logging.NullHandler"><code class="xref py py-class docutils literal notranslate"><span class="pre">logging.NullHandler</span></code></a>

  469. class for applications that are not using logging but are calling

  470. library code that does.  Setting-up a null handler will suppress

  471. spurious warnings such as “No handlers could be found for logger foo”:</p>

  472. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">NullHandler</span><span class="p">()</span>

  473. <span class="gp">&gt;&gt;&gt; </span><span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s2">&quot;foo&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">h</span><span class="p">)</span>

  474. </pre></div>

  475. </div>

  476. <p>(Contributed by Vinay Sajip; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4384">bpo-4384</a>).</p>

  477. </li>

  478. <li><p>The <a class="reference internal" href="../library/runpy.html#module-runpy" title="runpy: Locate and run Python modules without importing them first."><code class="xref py py-mod docutils literal notranslate"><span class="pre">runpy</span></code></a> module which supports the <code class="docutils literal notranslate"><span class="pre">-m</span></code> command line switch

  479. now supports the execution of packages by looking for and executing

  480. a <code class="docutils literal notranslate"><span class="pre">__main__</span></code> submodule when a package name is supplied.</p>

  481. <p>(Contributed by Andi Vajda; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4195">bpo-4195</a>.)</p>

  482. </li>

  483. <li><p>The <a class="reference internal" href="../library/pdb.html#module-pdb" title="pdb: The Python debugger for interactive interpreters."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pdb</span></code></a> module can now access and display source code loaded via

  484. <a class="reference internal" href="../library/zipimport.html#module-zipimport" title="zipimport: Support for importing Python modules from ZIP archives."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zipimport</span></code></a> (or any other conformant <span class="target" id="index-2"></span><a class="pep reference external" href="https://peps.python.org/pep-0302/"><strong>PEP 302</strong></a> loader).</p>

  485. <p>(Contributed by Alexander Belopolsky; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4201">bpo-4201</a>.)</p>

  486. </li>

  487. <li><p><a class="reference internal" href="../library/functools.html#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">functools.partial</span></code></a> objects can now be pickled.</p></li>

  488. </ul>

  489. <blockquote>

  490. <div><p>(Suggested by Antoine Pitrou and Jesse Noller.  Implemented by

  491. Jack Diederich; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5228">bpo-5228</a>.)</p>

  492. </div></blockquote>

  493. <ul>

  494. <li><p>Add <a class="reference internal" href="../library/pydoc.html#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pydoc</span></code></a> help topics for symbols so that <code class="docutils literal notranslate"><span class="pre">help('&#64;')</span></code>

  495. works as expected in the interactive environment.</p>

  496. <p>(Contributed by David Laban; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4739">bpo-4739</a>.)</p>

  497. </li>

  498. <li><p>The <a class="reference internal" href="../library/unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">unittest</span></code></a> module now supports skipping individual tests or classes

  499. of tests. And it supports marking a test as an expected failure, a test that

  500. is known to be broken, but shouldn’t be counted as a failure on a

  501. TestResult:</p>

  502. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">TestGizmo</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span>

  503. 

  504.     <span class="nd">@unittest</span><span class="o">.</span><span class="n">skipUnless</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">platform</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s2">&quot;win&quot;</span><span class="p">),</span> <span class="s2">&quot;requires Windows&quot;</span><span class="p">)</span>

  505.     <span class="k">def</span> <span class="nf">test_gizmo_on_windows</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>

  506.         <span class="o">...</span>

  507. 

  508.     <span class="nd">@unittest</span><span class="o">.</span><span class="n">expectedFailure</span>

  509.     <span class="k">def</span> <span class="nf">test_gimzo_without_required_library</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>

  510.         <span class="o">...</span>

  511. </pre></div>

  512. </div>

  513. <p>Also, tests for exceptions have been builtout to work with context managers

  514. using the <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement:</p>

  515. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">test_division_by_zero</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>

  516.     <span class="k">with</span> <span class="bp">self</span><span class="o">.</span><span class="n">assertRaises</span><span class="p">(</span><span class="ne">ZeroDivisionError</span><span class="p">):</span>

  517.         <span class="n">x</span> <span class="o">/</span> <span class="mi">0</span>

  518. </pre></div>

  519. </div>

  520. <p>In addition, several new assertion methods were added including

  521. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertSetEqual" title="unittest.TestCase.assertSetEqual"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertSetEqual()</span></code></a>,

  522. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertDictEqual" title="unittest.TestCase.assertDictEqual"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertDictEqual()</span></code></a>,

  523. <code class="xref py py-meth docutils literal notranslate"><span class="pre">assertDictContainsSubset()</span></code>,

  524. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertListEqual" title="unittest.TestCase.assertListEqual"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertListEqual()</span></code></a>,

  525. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertTupleEqual" title="unittest.TestCase.assertTupleEqual"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertTupleEqual()</span></code></a>,

  526. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertSequenceEqual" title="unittest.TestCase.assertSequenceEqual"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertSequenceEqual()</span></code></a>,

  527. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertRaisesRegex" title="unittest.TestCase.assertRaisesRegex"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertRaisesRegexp()</span></code></a>,

  528. <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertIsNone" title="unittest.TestCase.assertIsNone"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertIsNone()</span></code></a>,

  529. and <a class="reference internal" href="../library/unittest.html#unittest.TestCase.assertIsNotNone" title="unittest.TestCase.assertIsNotNone"><code class="xref py py-meth docutils literal notranslate"><span class="pre">assertIsNotNone()</span></code></a>.</p>

  530. <p>(Contributed by Benjamin Peterson and Antoine Pitrou.)</p>

  531. </li>

  532. <li><p>The <a class="reference internal" href="../library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">io</span></code></a> module has three new constants for the <a class="reference internal" href="../library/io.html#io.IOBase.seek" title="io.IOBase.seek"><code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code></a>

  533. method: <a class="reference internal" href="../library/os.html#os.SEEK_SET" title="os.SEEK_SET"><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_SET</span></code></a>, <a class="reference internal" href="../library/os.html#os.SEEK_CUR" title="os.SEEK_CUR"><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_CUR</span></code></a>, and <a class="reference internal" href="../library/os.html#os.SEEK_END" title="os.SEEK_END"><code class="xref py py-data docutils literal notranslate"><span class="pre">SEEK_END</span></code></a>.</p></li>

  534. <li><p>The <a class="reference internal" href="../library/sys.html#sys.version_info" title="sys.version_info"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.version_info</span></code></a> tuple is now a named tuple:</p>

  535. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">sys</span><span class="o">.</span><span class="n">version_info</span>

  536. <span class="go">sys.version_info(major=3, minor=1, micro=0, releaselevel=&#39;alpha&#39;, serial=2)</span>

  537. </pre></div>

  538. </div>

  539. <p>(Contributed by Ross Light; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4285">bpo-4285</a>.)</p>

  540. </li>

  541. <li><p>The <a class="reference internal" href="../library/nntplib.html#module-nntplib" title="nntplib: NNTP protocol client (requires sockets). (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">nntplib</span></code></a> and <a class="reference internal" href="../library/imaplib.html#module-imaplib" title="imaplib: IMAP4 protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">imaplib</span></code></a> modules now support IPv6.</p>

  542. <p>(Contributed by Derek Morr; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=1655">bpo-1655</a> and <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=1664">bpo-1664</a>.)</p>

  543. </li>

  544. <li><p>The <a class="reference internal" href="../library/pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> module has been adapted for better interoperability with

  545. Python 2.x when used with protocol 2 or lower.  The reorganization of the

  546. standard library changed the formal reference for many objects.  For

  547. example, <code class="docutils literal notranslate"><span class="pre">__builtin__.set</span></code> in Python 2 is called <code class="docutils literal notranslate"><span class="pre">builtins.set</span></code> in Python

  548. 3. This change confounded efforts to share data between different versions of

  549. Python.  But now when protocol 2 or lower is selected, the pickler will

  550. automatically use the old Python 2 names for both loading and dumping. This

  551. remapping is turned-on by default but can be disabled with the <em>fix_imports</em>

  552. option:</p>

  553. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">s</span> <span class="o">=</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>

  554. <span class="gp">&gt;&gt;&gt; </span><span class="n">pickle</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">protocol</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span>

  555. <span class="go">b&#39;c__builtin__\nset\np0\n((lp1\nL1L\naL2L\naL3L\natp2\nRp3\n.&#39;</span>

  556. <span class="gp">&gt;&gt;&gt; </span><span class="n">pickle</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">protocol</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span> <span class="n">fix_imports</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>

  557. <span class="go">b&#39;cbuiltins\nset\np0\n((lp1\nL1L\naL2L\naL3L\natp2\nRp3\n.&#39;</span>

  558. </pre></div>

  559. </div>

  560. <p>An unfortunate but unavoidable side-effect of this change is that protocol 2

  561. pickles produced by Python 3.1 won’t be readable with Python 3.0. The latest

  562. pickle protocol, protocol 3, should be used when migrating data between

  563. Python 3.x implementations, as it doesn’t attempt to remain compatible with

  564. Python 2.x.</p>

  565. <p>(Contributed by Alexandre Vassalotti and Antoine Pitrou, <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=6137">bpo-6137</a>.)</p>

  566. </li>

  567. <li><p>A new module, <a class="reference internal" href="../library/importlib.html#module-importlib" title="importlib: The implementation of the import machinery."><code class="xref py py-mod docutils literal notranslate"><span class="pre">importlib</span></code></a> was added.  It provides a complete, portable,

  568. pure Python reference implementation of the <a class="reference internal" href="../reference/simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">import</span></code></a> statement and its

  569. counterpart, the <a class="reference internal" href="../library/functions.html#import__" title="__import__"><code class="xref py py-func docutils literal notranslate"><span class="pre">__import__()</span></code></a> function.  It represents a substantial

  570. step forward in documenting and defining the actions that take place during

  571. imports.</p>

  572. <p>(Contributed by Brett Cannon.)</p>

  573. </li>

  574. </ul>

  575. </section>

  576. <section id="optimizations">

  577. <h2>Optimizations<a class="headerlink" href="#optimizations" title="Link to this heading">¶</a></h2>

  578. <p>Major performance enhancements have been added:</p>

  579. <ul>

  580. <li><p>The new I/O library (as defined in <span class="target" id="index-3"></span><a class="pep reference external" href="https://peps.python.org/pep-3116/"><strong>PEP 3116</strong></a>) was mostly written in

  581. Python and quickly proved to be a problematic bottleneck in Python 3.0.

  582. In Python 3.1, the I/O library has been entirely rewritten in C and is

  583. 2 to 20 times faster depending on the task at hand. The pure Python

  584. version is still available for experimentation purposes through

  585. the <code class="docutils literal notranslate"><span class="pre">_pyio</span></code> module.</p>

  586. <p>(Contributed by Amaury Forgeot d’Arc and Antoine Pitrou.)</p>

  587. </li>

  588. <li><p>Added a heuristic so that tuples and dicts containing only untrackable objects

  589. are not tracked by the garbage collector. This can reduce the size of

  590. collections and therefore the garbage collection overhead on long-running

  591. programs, depending on their particular use of datatypes.</p>

  592. <p>(Contributed by Antoine Pitrou, <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4688">bpo-4688</a>.)</p>

  593. </li>

  594. <li><p>Enabling a configure option named <code class="docutils literal notranslate"><span class="pre">--with-computed-gotos</span></code>

  595. on compilers that support it (notably: gcc, SunPro, icc), the bytecode

  596. evaluation loop is compiled with a new dispatch mechanism which gives

  597. speedups of up to 20%, depending on the system, the compiler, and

  598. the benchmark.</p>

  599. <p>(Contributed by Antoine Pitrou along with a number of other participants,

  600. <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4753">bpo-4753</a>).</p>

  601. </li>

  602. <li><p>The decoding of UTF-8, UTF-16 and LATIN-1 is now two to four times

  603. faster.</p>

  604. <p>(Contributed by Antoine Pitrou and Amaury Forgeot d’Arc, <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4868">bpo-4868</a>.)</p>

  605. </li>

  606. <li><p>The <a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> module now has a C extension to substantially improve

  607. its performance.  In addition, the API was modified so that json works

  608. only with <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>, not with <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.  That change makes the

  609. module closely match the <a class="reference external" href="https://json.org/">JSON specification</a>

  610. which is defined in terms of Unicode.</p>

  611. <p>(Contributed by Bob Ippolito and converted to Py3.1 by Antoine Pitrou

  612. and Benjamin Peterson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4136">bpo-4136</a>.)</p>

  613. </li>

  614. <li><p>Unpickling now interns the attribute names of pickled objects.  This saves

  615. memory and allows pickles to be smaller.</p>

  616. <p>(Contributed by Jake McGuire and Antoine Pitrou; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5084">bpo-5084</a>.)</p>

  617. </li>

  618. </ul>

  619. </section>

  620. <section id="idle">

  621. <h2>IDLE<a class="headerlink" href="#idle" title="Link to this heading">¶</a></h2>

  622. <ul>

  623. <li><p>IDLE’s format menu now provides an option to strip trailing whitespace

  624. from a source file.</p>

  625. <p>(Contributed by Roger D. Serwy; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5150">bpo-5150</a>.)</p>

  626. </li>

  627. </ul>

  628. </section>

  629. <section id="build-and-c-api-changes">

  630. <h2>Build and C API Changes<a class="headerlink" href="#build-and-c-api-changes" title="Link to this heading">¶</a></h2>

  631. <p>Changes to Python’s build process and to the C API include:</p>

  632. <ul>

  633. <li><p>Integers are now stored internally either in base <code class="docutils literal notranslate"><span class="pre">2**15</span></code> or in base

  634. <code class="docutils literal notranslate"><span class="pre">2**30</span></code>, the base being determined at build time.  Previously, they

  635. were always stored in base <code class="docutils literal notranslate"><span class="pre">2**15</span></code>.  Using base <code class="docutils literal notranslate"><span class="pre">2**30</span></code> gives

  636. significant performance improvements on 64-bit machines, but

  637. benchmark results on 32-bit machines have been mixed.  Therefore,

  638. the default is to use base <code class="docutils literal notranslate"><span class="pre">2**30</span></code> on 64-bit machines and base <code class="docutils literal notranslate"><span class="pre">2**15</span></code>

  639. on 32-bit machines; on Unix, there’s a new configure option

  640. <code class="docutils literal notranslate"><span class="pre">--enable-big-digits</span></code> that can be used to override this default.</p>

  641. <p>Apart from the performance improvements this change should be invisible to

  642. end users, with one exception: for testing and debugging purposes there’s a

  643. new <a class="reference internal" href="../library/sys.html#sys.int_info" title="sys.int_info"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.int_info</span></code></a> that provides information about the

  644. internal format, giving the number of bits per digit and the size in bytes

  645. of the C type used to store each digit:</p>

  646. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">sys</span>

  647. <span class="gp">&gt;&gt;&gt; </span><span class="n">sys</span><span class="o">.</span><span class="n">int_info</span>

  648. <span class="go">sys.int_info(bits_per_digit=30, sizeof_digit=4)</span>

  649. </pre></div>

  650. </div>

  651. <p>(Contributed by Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4258">bpo-4258</a>.)</p>

  652. </li>

  653. <li><p>The <a class="reference internal" href="../c-api/long.html#c.PyLong_AsUnsignedLongLong" title="PyLong_AsUnsignedLongLong"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyLong_AsUnsignedLongLong()</span></code></a> function now handles a negative

  654. <em>pylong</em> by raising <a class="reference internal" href="../library/exceptions.html#OverflowError" title="OverflowError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OverflowError</span></code></a> instead of <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p>

  655. <p>(Contributed by Mark Dickinson and Lisandro Dalcrin; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5175">bpo-5175</a>.)</p>

  656. </li>

  657. <li><p>Deprecated <code class="xref c c-func docutils literal notranslate"><span class="pre">PyNumber_Int()</span></code>.  Use <a class="reference internal" href="../c-api/number.html#c.PyNumber_Long" title="PyNumber_Long"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyNumber_Long()</span></code></a> instead.</p>

  658. <p>(Contributed by Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=4910">bpo-4910</a>.)</p>

  659. </li>

  660. <li><p>Added a new <a class="reference internal" href="../c-api/conversion.html#c.PyOS_string_to_double" title="PyOS_string_to_double"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_string_to_double()</span></code></a> function to replace the

  661. deprecated functions <code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_ascii_strtod()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_ascii_atof()</span></code>.</p>

  662. <p>(Contributed by Mark Dickinson; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5914">bpo-5914</a>.)</p>

  663. </li>

  664. <li><p>Added <a class="reference internal" href="../c-api/capsule.html#c.PyCapsule" title="PyCapsule"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCapsule</span></code></a> as a replacement for the <code class="xref c c-type docutils literal notranslate"><span class="pre">PyCObject</span></code> API.

  665. The principal difference is that the new type has a well defined interface

  666. for passing typing safety information and a less complicated signature

  667. for calling a destructor.  The old type had a problematic API and is now

  668. deprecated.</p>

  669. <p>(Contributed by Larry Hastings; <a class="reference external" href="https://bugs.python.org/issue?&#64;action=redirect&amp;bpo=5630">bpo-5630</a>.)</p>

  670. </li>

  671. </ul>

  672. </section>

  673. <section id="porting-to-python-3-1">

  674. <h2>Porting to Python 3.1<a class="headerlink" href="#porting-to-python-3-1" title="Link to this heading">¶</a></h2>

  675. <p>This section lists previously described changes and other bugfixes

  676. that may require changes to your code:</p>

  677. <ul>

  678. <li><p>The new floating point string representations can break existing doctests.

  679. For example:</p>

  680. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">e</span><span class="p">():</span>

  681. <span class="w">    </span><span class="sd">&#39;&#39;&#39;Compute the base of natural logarithms.</span>

  682. 

  683. <span class="sd">    &gt;&gt;&gt; e()</span>

  684. <span class="sd">    2.7182818284590451</span>

  685. 

  686. <span class="sd">    &#39;&#39;&#39;</span>

  687.     <span class="k">return</span> <span class="nb">sum</span><span class="p">(</span><span class="mi">1</span><span class="o">/</span><span class="n">math</span><span class="o">.</span><span class="n">factorial</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">reversed</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="mi">30</span><span class="p">)))</span>

  688. 

  689. <span class="n">doctest</span><span class="o">.</span><span class="n">testmod</span><span class="p">()</span>

  690. 

  691. <span class="o">**********************************************************************</span>

  692. <span class="n">Failed</span> <span class="n">example</span><span class="p">:</span>

  693.     <span class="n">e</span><span class="p">()</span>

  694. <span class="n">Expected</span><span class="p">:</span>

  695.     <span class="mf">2.7182818284590451</span>

  696. <span class="n">Got</span><span class="p">:</span>

  697.     <span class="mf">2.718281828459045</span>

  698. <span class="o">**********************************************************************</span>

  699. </pre></div>

  700. </div>

  701. </li>

  702. <li><p>The automatic name remapping in the pickle module for protocol 2 or lower can

  703. make Python 3.1 pickles unreadable in Python 3.0.  One solution is to use

  704. protocol 3.  Another solution is to set the <em>fix_imports</em> option to <code class="docutils literal notranslate"><span class="pre">False</span></code>.

  705. See the discussion above for more details.</p></li>

  706. </ul>

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