<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title>functools — Higher-order functions and operations on callable objects — Python 3.7.4 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.7.4 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="operator — Standard operators as functions" href="operator.html" /> <link rel="prev" title="itertools — Functions creating iterators for efficient looping" href="itertools.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/library/functools.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <script type="text/javascript" src="../_static/switchers.js"></script> <style> @media only screen { table.full-width-table { width: 100%; } } </style> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="operator.html" title="operator — Standard operators as functions" accesskey="N">next</a> |</li> <li class="right" > <a href="itertools.html" title="itertools — Functions creating iterators for efficient looping" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <span class="language_switcher_placeholder">en</span> <span class="version_switcher_placeholder">3.7.4</span> <a href="../index.html">Documentation </a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="functional.html" accesskey="U">Functional Programming Modules</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-functools"> <span id="functools-higher-order-functions-and-operations-on-callable-objects"></span><h1><a class="reference internal" href="#module-functools" title="functools: Higher-order functions and operations on callable objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">functools</span></code></a> — Higher-order functions and operations on callable objects<a class="headerlink" href="#module-functools" title="Permalink to this headline">¶</a></h1> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/functools.py">Lib/functools.py</a></p> <hr class="docutils" /> <p>The <a class="reference internal" href="#module-functools" title="functools: Higher-order functions and operations on callable objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">functools</span></code></a> module is for higher-order functions: functions that act on or return other functions. In general, any callable object can be treated as a function for the purposes of this module.</p> <p>The <a class="reference internal" href="#module-functools" title="functools: Higher-order functions and operations on callable objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">functools</span></code></a> module defines the following functions:</p> <dl class="function"> <dt id="functools.cmp_to_key"> <code class="descclassname">functools.</code><code class="descname">cmp_to_key</code><span class="sig-paren">(</span><em>func</em><span class="sig-paren">)</span><a class="headerlink" href="#functools.cmp_to_key" title="Permalink to this definition">¶</a></dt> <dd><p>Transform an old-style comparison function to a <a class="reference internal" href="../glossary.html#term-key-function"><span class="xref std std-term">key function</span></a>. Used with tools that accept key functions (such as <a class="reference internal" href="functions.html#sorted" title="sorted"><code class="xref py py-func docutils literal notranslate"><span class="pre">sorted()</span></code></a>, <a class="reference internal" href="functions.html#min" title="min"><code class="xref py py-func docutils literal notranslate"><span class="pre">min()</span></code></a>, <a class="reference internal" href="functions.html#max" title="max"><code class="xref py py-func docutils literal notranslate"><span class="pre">max()</span></code></a>, <a class="reference internal" href="heapq.html#heapq.nlargest" title="heapq.nlargest"><code class="xref py py-func docutils literal notranslate"><span class="pre">heapq.nlargest()</span></code></a>, <a class="reference internal" href="heapq.html#heapq.nsmallest" title="heapq.nsmallest"><code class="xref py py-func docutils literal notranslate"><span class="pre">heapq.nsmallest()</span></code></a>, <a class="reference internal" href="itertools.html#itertools.groupby" title="itertools.groupby"><code class="xref py py-func docutils literal notranslate"><span class="pre">itertools.groupby()</span></code></a>). This function is primarily used as a transition tool for programs being converted from Python 2 which supported the use of comparison functions.</p> <p>A comparison function is any callable that accept two arguments, compares them, and returns a negative number for less-than, zero for equality, or a positive number for greater-than. A key function is a callable that accepts one argument and returns another value to be used as the sort key.</p> <p>Example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nb">sorted</span><span class="p">(</span><span class="n">iterable</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="n">cmp_to_key</span><span class="p">(</span><span class="n">locale</span><span class="o">.</span><span class="n">strcoll</span><span class="p">))</span> <span class="c1"># locale-aware sort order</span> </pre></div> </div> <p>For sorting examples and a brief sorting tutorial, see <a class="reference internal" href="../howto/sorting.html#sortinghowto"><span class="std std-ref">Sorting HOW TO</span></a>.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="functools.lru_cache"> <code class="descclassname">@</code><code class="descclassname">functools.</code><code class="descname">lru_cache</code><span class="sig-paren">(</span><em>maxsize=128</em>, <em>typed=False</em><span class="sig-paren">)</span><a class="headerlink" href="#functools.lru_cache" title="Permalink to this definition">¶</a></dt> <dd><p>Decorator to wrap a function with a memoizing callable that saves up to the <em>maxsize</em> most recent calls. It can save time when an expensive or I/O bound function is periodically called with the same arguments.</p> <p>Since a dictionary is used to cache results, the positional and keyword arguments to the function must be hashable.</p> <p>Distinct argument patterns may be considered to be distinct calls with separate cache entries. For example, <cite>f(a=1, b=2)</cite> and <cite>f(b=2, a=1)</cite> differ in their keyword argument order and may have two separate cache entries.</p> <p>If <em>maxsize</em> is set to <code class="docutils literal notranslate"><span class="pre">None</span></code>, the LRU feature is disabled and the cache can grow without bound. The LRU feature performs best when <em>maxsize</em> is a power-of-two.</p> <p>If <em>typed</em> is set to true, function arguments of different types will be cached separately. For example, <code class="docutils literal notranslate"><span class="pre">f(3)</span></code> and <code class="docutils literal notranslate"><span class="pre">f(3.0)</span></code> will be treated as distinct calls with distinct results.</p> <p>To help measure the effectiveness of the cache and tune the <em>maxsize</em> parameter, the wrapped function is instrumented with a <code class="xref py py-func docutils literal notranslate"><span class="pre">cache_info()</span></code> function that returns a <a class="reference internal" href="../glossary.html#term-named-tuple"><span class="xref std std-term">named tuple</span></a> showing <em>hits</em>, <em>misses</em>, <em>maxsize</em> and <em>currsize</em>. In a multi-threaded environment, the hits and misses are approximate.</p> <p>The decorator also provides a <code class="xref py py-func docutils literal notranslate"><span class="pre">cache_clear()</span></code> function for clearing or invalidating the cache.</p> <p>The original underlying function is accessible through the <code class="xref py py-attr docutils literal notranslate"><span class="pre">__wrapped__</span></code> attribute. This is useful for introspection, for bypassing the cache, or for rewrapping the function with a different cache.</p> <p>An <a class="reference external" href="https://en.wikipedia.org/wiki/Cache_algorithms#Examples">LRU (least recently used) cache</a> works best when the most recent calls are the best predictors of upcoming calls (for example, the most popular articles on a news server tend to change each day). The cache’s size limit assures that the cache does not grow without bound on long-running processes such as web servers.</p> <p>In general, the LRU cache should only be used when you want to reuse previously computed values. Accordingly, it doesn’t make sense to cache functions with side-effects, functions that need to create distinct mutable objects on each call, or impure functions such as time() or random().</p> <p>Example of an LRU cache for static web content:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nd">@lru_cache</span><span class="p">(</span><span class="n">maxsize</span><span class="o">=</span><span class="mi">32</span><span class="p">)</span> <span class="k">def</span> <span class="nf">get_pep</span><span class="p">(</span><span class="n">num</span><span class="p">):</span> <span class="s1">'Retrieve text of a Python Enhancement Proposal'</span> <span class="n">resource</span> <span class="o">=</span> <span class="s1">'http://www.python.org/dev/peps/pep-</span><span class="si">%04d</span><span class="s1">/'</span> <span class="o">%</span> <span class="n">num</span> <span class="k">try</span><span class="p">:</span> <span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">resource</span><span class="p">)</span> <span class="k">as</span> <span class="n">s</span><span class="p">:</span> <span class="k">return</span> <span class="n">s</span><span class="o">.</span><span class="n">read</span><span class="p">()</span> <span class="k">except</span> <span class="n">urllib</span><span class="o">.</span><span class="n">error</span><span class="o">.</span><span class="n">HTTPError</span><span class="p">:</span> <span class="k">return</span> <span class="s1">'Not Found'</span> <span class="o">>>></span> <span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">290</span><span class="p">,</span> <span class="mi">308</span><span class="p">,</span> <span class="mi">320</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">218</span><span class="p">,</span> <span class="mi">320</span><span class="p">,</span> <span class="mi">279</span><span class="p">,</span> <span class="mi">289</span><span class="p">,</span> <span class="mi">320</span><span class="p">,</span> <span class="mi">9991</span><span class="p">:</span> <span class="o">...</span> <span class="n">pep</span> <span class="o">=</span> <span class="n">get_pep</span><span class="p">(</span><span class="n">n</span><span class="p">)</span> <span class="o">...</span> <span class="nb">print</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">pep</span><span class="p">))</span> <span class="o">>>></span> <span class="n">get_pep</span><span class="o">.</span><span class="n">cache_info</span><span class="p">()</span> <span class="n">CacheInfo</span><span class="p">(</span><span class="n">hits</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">misses</span><span class="o">=</span><span class="mi">8</span><span class="p">,</span> <span class="n">maxsize</span><span class="o">=</span><span class="mi">32</span><span class="p">,</span> <span class="n">currsize</span><span class="o">=</span><span class="mi">8</span><span class="p">)</span> </pre></div> </div> <p>Example of efficiently computing <a class="reference external" href="https://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers</a> using a cache to implement a <a class="reference external" href="https://en.wikipedia.org/wiki/Dynamic_programming">dynamic programming</a> technique:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nd">@lru_cache</span><span class="p">(</span><span class="n">maxsize</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span> <span class="k">def</span> <span class="nf">fib</span><span class="p">(</span><span class="n">n</span><span class="p">):</span> <span class="k">if</span> <span class="n">n</span> <span class="o"><</span> <span class="mi">2</span><span class="p">:</span> <span class="k">return</span> <span class="n">n</span> <span class="k">return</span> <span class="n">fib</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">fib</span><span class="p">(</span><span class="n">n</span><span class="o">-</span><span class="mi">2</span><span class="p">)</span> <span class="o">>>></span> <span class="p">[</span><span class="n">fib</span><span class="p">(</span><span class="n">n</span><span class="p">)</span> <span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">16</span><span class="p">)]</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">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">21</span><span class="p">,</span> <span class="mi">34</span><span class="p">,</span> <span class="mi">55</span><span class="p">,</span> <span class="mi">89</span><span class="p">,</span> <span class="mi">144</span><span class="p">,</span> <span class="mi">233</span><span class="p">,</span> <span class="mi">377</span><span class="p">,</span> <span class="mi">610</span><span class="p">]</span> <span class="o">>>></span> <span class="n">fib</span><span class="o">.</span><span class="n">cache_info</span><span class="p">()</span> <span class="n">CacheInfo</span><span class="p">(</span><span class="n">hits</span><span class="o">=</span><span class="mi">28</span><span class="p">,</span> <span class="n">misses</span><span class="o">=</span><span class="mi">16</span><span class="p">,</span> <span class="n">maxsize</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">currsize</span><span class="o">=</span><span class="mi">16</span><span class="p">)</span> </pre></div> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.2.</span></p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.3: </span>Added the <em>typed</em> option.</p> </div> </dd></dl> <dl class="function"> <dt id="functools.total_ordering"> <code class="descclassname">@</code><code class="descclassname">functools.</code><code class="descname">total_ordering</code><a class="headerlink" href="#functools.total_ordering" title="Permalink to this definition">¶</a></dt> <dd><p>Given a class defining one or more rich comparison ordering methods, this class decorator supplies the rest. This simplifies the effort involved in specifying all of the possible rich comparison operations:</p> <p>The class must define one of <a class="reference internal" href="../reference/datamodel.html#object.__lt__" title="object.__lt__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__lt__()</span></code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__le__" title="object.__le__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__le__()</span></code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__gt__" title="object.__gt__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__gt__()</span></code></a>, or <a class="reference internal" href="../reference/datamodel.html#object.__ge__" title="object.__ge__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__ge__()</span></code></a>. In addition, the class should supply an <a class="reference internal" href="../reference/datamodel.html#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__eq__()</span></code></a> method.</p> <p>For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nd">@total_ordering</span> <span class="k">class</span> <span class="nc">Student</span><span class="p">:</span> <span class="k">def</span> <span class="nf">_is_valid_operand</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span> <span class="k">return</span> <span class="p">(</span><span class="nb">hasattr</span><span class="p">(</span><span class="n">other</span><span class="p">,</span> <span class="s2">"lastname"</span><span class="p">)</span> <span class="ow">and</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">other</span><span class="p">,</span> <span class="s2">"firstname"</span><span class="p">))</span> <span class="k">def</span> <span class="nf">__eq__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span> <span class="k">if</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">_is_valid_operand</span><span class="p">(</span><span class="n">other</span><span class="p">):</span> <span class="k">return</span> <span class="bp">NotImplemented</span> <span class="k">return</span> <span class="p">((</span><span class="bp">self</span><span class="o">.</span><span class="n">lastname</span><span class="o">.</span><span class="n">lower</span><span class="p">(),</span> <span class="bp">self</span><span class="o">.</span><span class="n">firstname</span><span class="o">.</span><span class="n">lower</span><span class="p">())</span> <span class="o">==</span> <span class="p">(</span><span class="n">other</span><span class="o">.</span><span class="n">lastname</span><span class="o">.</span><span class="n">lower</span><span class="p">(),</span> <span class="n">other</span><span class="o">.</span><span class="n">firstname</span><span class="o">.</span><span class="n">lower</span><span class="p">()))</span> <span class="k">def</span> <span class="nf">__lt__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span> <span class="k">if</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">_is_valid_operand</span><span class="p">(</span><span class="n">other</span><span class="p">):</span> <span class="k">return</span> <span class="bp">NotImplemented</span> <span class="k">return</span> <span class="p">((</span><span class="bp">self</span><span class="o">.</span><span class="n">lastname</span><span class="o">.</span><span class="n">lower</span><span class="p">(),</span> <span class="bp">self</span><span class="o">.</span><span class="n">firstname</span><span class="o">.</span><span class="n">lower</span><span class="p">())</span> <span class="o"><</span> <span class="p">(</span><span class="n">other</span><span class="o">.</span><span class="n">lastname</span><span class="o">.</span><span class="n">lower</span><span class="p">(),</span> <span class="n">other</span><span class="o">.</span><span class="n">firstname</span><span class="o">.</span><span class="n">lower</span><span class="p">()))</span> </pre></div> </div> <div class="admonition note"> <p class="admonition-title">Note</p> <p>While this decorator makes it easy to create well behaved totally ordered types, it <em>does</em> come at the cost of slower execution and more complex stack traces for the derived comparison methods. If performance benchmarking indicates this is a bottleneck for a given application, implementing all six rich comparison methods instead is likely to provide an easy speed boost.</p> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.2.</span></p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.4: </span>Returning NotImplemented from the underlying comparison function for unrecognised types is now supported.</p> </div> </dd></dl> <dl class="function"> <dt id="functools.partial"> <code class="descclassname">functools.</code><code class="descname">partial</code><span class="sig-paren">(</span><em>func</em>, <em>*args</em>, <em>**keywords</em><span class="sig-paren">)</span><a class="headerlink" href="#functools.partial" title="Permalink to this definition">¶</a></dt> <dd><p>Return a new <a class="reference internal" href="#partial-objects"><span class="std std-ref">partial object</span></a> which when called will behave like <em>func</em> called with the positional arguments <em>args</em> and keyword arguments <em>keywords</em>. If more arguments are supplied to the call, they are appended to <em>args</em>. If additional keyword arguments are supplied, they extend and override <em>keywords</em>. Roughly equivalent to:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">partial</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">keywords</span><span class="p">):</span> <span class="k">def</span> <span class="nf">newfunc</span><span class="p">(</span><span class="o">*</span><span class="n">fargs</span><span class="p">,</span> <span class="o">**</span><span class="n">fkeywords</span><span class="p">):</span> <span class="n">newkeywords</span> <span class="o">=</span> <span class="n">keywords</span><span class="o">.</span><span class="n">copy</span><span class="p">()</span> <span class="n">newkeywords</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">fkeywords</span><span class="p">)</span> <span class="k">return</span> <span class="n">func</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">*</span><span class="n">fargs</span><span class="p">,</span> <span class="o">**</span><span class="n">newkeywords</span><span class="p">)</span> <span class="n">newfunc</span><span class="o">.</span><span class="n">func</span> <span class="o">=</span> <span class="n">func</span> <span class="n">newfunc</span><span class="o">.</span><span class="n">args</span> <span class="o">=</span> <span class="n">args</span> <span class="n">newfunc</span><span class="o">.</span><span class="n">keywords</span> <span class="o">=</span> <span class="n">keywords</span> <span class="k">return</span> <span class="n">newfunc</span> </pre></div> </div> <p>The <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate"><span class="pre">partial()</span></code></a> is used for partial function application which “freezes” some portion of a function’s arguments and/or keywords resulting in a new object with a simplified signature. For example, <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate"><span class="pre">partial()</span></code></a> can be used to create a callable that behaves like the <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate"><span class="pre">int()</span></code></a> function where the <em>base</em> argument defaults to two:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">functools</span> <span class="k">import</span> <span class="n">partial</span> <span class="gp">>>> </span><span class="n">basetwo</span> <span class="o">=</span> <span class="n">partial</span><span class="p">(</span><span class="nb">int</span><span class="p">,</span> <span class="n">base</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">basetwo</span><span class="o">.</span><span class="vm">__doc__</span> <span class="o">=</span> <span class="s1">'Convert base 2 string to an int.'</span> <span class="gp">>>> </span><span class="n">basetwo</span><span class="p">(</span><span class="s1">'10010'</span><span class="p">)</span> <span class="go">18</span> </pre></div> </div> </dd></dl> <dl class="class"> <dt id="functools.partialmethod"> <em class="property">class </em><code class="descclassname">functools.</code><code class="descname">partialmethod</code><span class="sig-paren">(</span><em>func</em>, <em>*args</em>, <em>**keywords</em><span class="sig-paren">)</span><a class="headerlink" href="#functools.partialmethod" title="Permalink to this definition">¶</a></dt> <dd><p>Return a new <a class="reference internal" href="#functools.partialmethod" title="functools.partialmethod"><code class="xref py py-class docutils literal notranslate"><span class="pre">partialmethod</span></code></a> descriptor which behaves like <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> except that it is designed to be used as a method definition rather than being directly callable.</p> <p><em>func</em> must be a <a class="reference internal" href="../glossary.html#term-descriptor"><span class="xref std std-term">descriptor</span></a> or a callable (objects which are both, like normal functions, are handled as descriptors).</p> <p>When <em>func</em> is a descriptor (such as a normal Python function, <a class="reference internal" href="functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">classmethod()</span></code></a>, <a class="reference internal" href="functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">staticmethod()</span></code></a>, <code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code> or another instance of <a class="reference internal" href="#functools.partialmethod" title="functools.partialmethod"><code class="xref py py-class docutils literal notranslate"><span class="pre">partialmethod</span></code></a>), calls to <code class="docutils literal notranslate"><span class="pre">__get__</span></code> are delegated to the underlying descriptor, and an appropriate <a class="reference internal" href="#partial-objects"><span class="std std-ref">partial object</span></a> returned as the result.</p> <p>When <em>func</em> is a non-descriptor callable, an appropriate bound method is created dynamically. This behaves like a normal Python function when used as a method: the <em>self</em> argument will be inserted as the first positional argument, even before the <em>args</em> and <em>keywords</em> supplied to the <a class="reference internal" href="#functools.partialmethod" title="functools.partialmethod"><code class="xref py py-class docutils literal notranslate"><span class="pre">partialmethod</span></code></a> constructor.</p> <p>Example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Cell</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">_alive</span> <span class="o">=</span> <span class="kc">False</span> <span class="gp">... </span> <span class="nd">@property</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">alive</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_alive</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">set_state</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">state</span><span class="p">):</span> <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">_alive</span> <span class="o">=</span> <span class="nb">bool</span><span class="p">(</span><span class="n">state</span><span class="p">)</span> <span class="gp">... </span> <span class="n">set_alive</span> <span class="o">=</span> <span class="n">partialmethod</span><span class="p">(</span><span class="n">set_state</span><span class="p">,</span> <span class="kc">True</span><span class="p">)</span> <span class="gp">... </span> <span class="n">set_dead</span> <span class="o">=</span> <span class="n">partialmethod</span><span class="p">(</span><span class="n">set_state</span><span class="p">,</span> <span class="kc">False</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">c</span> <span class="o">=</span> <span class="n">Cell</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">c</span><span class="o">.</span><span class="n">alive</span> <span class="go">False</span> <span class="gp">>>> </span><span class="n">c</span><span class="o">.</span><span class="n">set_alive</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">c</span><span class="o">.</span><span class="n">alive</span> <span class="go">True</span> </pre></div> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> </dd></dl> <dl class="function"> <dt id="functools.reduce"> <code class="descclassname">functools.</code><code class="descname">reduce</code><span class="sig-paren">(</span><em>function</em>, <em>iterable</em><span class="optional">[</span>, <em>initializer</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#functools.reduce" title="Permalink to this definition">¶</a></dt> <dd><p>Apply <em>function</em> of two arguments cumulatively to the items of <em>sequence</em>, from left to right, so as to reduce the sequence to a single value. For example, <code class="docutils literal notranslate"><span class="pre">reduce(lambda</span> <span class="pre">x,</span> <span class="pre">y:</span> <span class="pre">x+y,</span> <span class="pre">[1,</span> <span class="pre">2,</span> <span class="pre">3,</span> <span class="pre">4,</span> <span class="pre">5])</span></code> calculates <code class="docutils literal notranslate"><span class="pre">((((1+2)+3)+4)+5)</span></code>. The left argument, <em>x</em>, is the accumulated value and the right argument, <em>y</em>, is the update value from the <em>sequence</em>. If the optional <em>initializer</em> is present, it is placed before the items of the sequence in the calculation, and serves as a default when the sequence is empty. If <em>initializer</em> is not given and <em>sequence</em> contains only one item, the first item is returned.</p> <p>Roughly equivalent to:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">reduce</span><span class="p">(</span><span class="n">function</span><span class="p">,</span> <span class="n">iterable</span><span class="p">,</span> <span class="n">initializer</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span> <span class="n">it</span> <span class="o">=</span> <span class="nb">iter</span><span class="p">(</span><span class="n">iterable</span><span class="p">)</span> <span class="k">if</span> <span class="n">initializer</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span> <span class="n">value</span> <span class="o">=</span> <span class="nb">next</span><span class="p">(</span><span class="n">it</span><span class="p">)</span> <span class="k">else</span><span class="p">:</span> <span class="n">value</span> <span class="o">=</span> <span class="n">initializer</span> <span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">it</span><span class="p">:</span> <span class="n">value</span> <span class="o">=</span> <span class="n">function</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">element</span><span class="p">)</span> <span class="k">return</span> <span class="n">value</span> </pre></div> </div> </dd></dl> <dl class="function"> <dt id="functools.singledispatch"> <code class="descclassname">@</code><code class="descclassname">functools.</code><code class="descname">singledispatch</code><a class="headerlink" href="#functools.singledispatch" title="Permalink to this definition">¶</a></dt> <dd><p>Transform a function into a <a class="reference internal" href="../glossary.html#term-single-dispatch"><span class="xref std std-term">single-dispatch</span></a> <a class="reference internal" href="../glossary.html#term-generic-function"><span class="xref std std-term">generic function</span></a>.</p> <p>To define a generic function, decorate it with the <code class="docutils literal notranslate"><span class="pre">@singledispatch</span></code> decorator. Note that the dispatch happens on the type of the first argument, create your function accordingly:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">functools</span> <span class="k">import</span> <span class="n">singledispatch</span> <span class="gp">>>> </span><span class="nd">@singledispatch</span> <span class="gp">... </span><span class="k">def</span> <span class="nf">fun</span><span class="p">(</span><span class="n">arg</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="n">verbose</span><span class="p">:</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Let me just say,"</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s2">" "</span><span class="p">)</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">arg</span><span class="p">)</span> </pre></div> </div> <p>To add overloaded implementations to the function, use the <code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code> attribute of the generic function. It is a decorator. For functions annotated with types, the decorator will infer the type of the first argument automatically:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@fun</span><span class="o">.</span><span class="n">register</span> <span class="gp">... </span><span class="k">def</span> <span class="nf">_</span><span class="p">(</span><span class="n">arg</span><span class="p">:</span> <span class="nb">int</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="n">verbose</span><span class="p">:</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Strength in numbers, eh?"</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s2">" "</span><span class="p">)</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">arg</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="nd">@fun</span><span class="o">.</span><span class="n">register</span> <span class="gp">... </span><span class="k">def</span> <span class="nf">_</span><span class="p">(</span><span class="n">arg</span><span class="p">:</span> <span class="nb">list</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="n">verbose</span><span class="p">:</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Enumerate this:"</span><span class="p">)</span> <span class="gp">... </span> <span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="n">arg</span><span class="p">):</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">elem</span><span class="p">)</span> </pre></div> </div> <p>For code which doesn’t use type annotations, the appropriate type argument can be passed explicitly to the decorator itself:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@fun</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">complex</span><span class="p">)</span> <span class="gp">... </span><span class="k">def</span> <span class="nf">_</span><span class="p">(</span><span class="n">arg</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="n">verbose</span><span class="p">:</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Better than complicated."</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s2">" "</span><span class="p">)</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">arg</span><span class="o">.</span><span class="n">real</span><span class="p">,</span> <span class="n">arg</span><span class="o">.</span><span class="n">imag</span><span class="p">)</span> <span class="gp">...</span> </pre></div> </div> <p>To enable registering lambdas and pre-existing functions, the <code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code> attribute can be used in a functional form:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">nothing</span><span class="p">(</span><span class="n">arg</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Nothing."</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">fun</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">type</span><span class="p">(</span><span class="kc">None</span><span class="p">),</span> <span class="n">nothing</span><span class="p">)</span> </pre></div> </div> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code> attribute returns the undecorated function which enables decorator stacking, pickling, as well as creating unit tests for each variant independently:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@fun</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">float</span><span class="p">)</span> <span class="gp">... </span><span class="nd">@fun</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">Decimal</span><span class="p">)</span> <span class="gp">... </span><span class="k">def</span> <span class="nf">fun_num</span><span class="p">(</span><span class="n">arg</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">False</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="n">verbose</span><span class="p">:</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Half of your number:"</span><span class="p">,</span> <span class="n">end</span><span class="o">=</span><span class="s2">" "</span><span class="p">)</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">arg</span> <span class="o">/</span> <span class="mi">2</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">fun_num</span> <span class="ow">is</span> <span class="n">fun</span> <span class="go">False</span> </pre></div> </div> <p>When called, the generic function dispatches on the type of the first argument:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">fun</span><span class="p">(</span><span class="s2">"Hello, world."</span><span class="p">)</span> <span class="go">Hello, world.</span> <span class="gp">>>> </span><span class="n">fun</span><span class="p">(</span><span class="s2">"test."</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="go">Let me just say, test.</span> <span class="gp">>>> </span><span class="n">fun</span><span class="p">(</span><span class="mi">42</span><span class="p">,</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="go">Strength in numbers, eh? 42</span> <span class="gp">>>> </span><span class="n">fun</span><span class="p">([</span><span class="s1">'spam'</span><span class="p">,</span> <span class="s1">'spam'</span><span class="p">,</span> <span class="s1">'eggs'</span><span class="p">,</span> <span class="s1">'spam'</span><span class="p">],</span> <span class="n">verbose</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="go">Enumerate this:</span> <span class="go">0 spam</span> <span class="go">1 spam</span> <span class="go">2 eggs</span> <span class="go">3 spam</span> <span class="gp">>>> </span><span class="n">fun</span><span class="p">(</span><span class="kc">None</span><span class="p">)</span> <span class="go">Nothing.</span> <span class="gp">>>> </span><span class="n">fun</span><span class="p">(</span><span class="mf">1.23</span><span class="p">)</span> <span class="go">0.615</span> </pre></div> </div> <p>Where there is no registered implementation for a specific type, its method resolution order is used to find a more generic implementation. The original function decorated with <code class="docutils literal notranslate"><span class="pre">@singledispatch</span></code> is registered for the base <code class="docutils literal notranslate"><span class="pre">object</span></code> type, which means it is used if no better implementation is found.</p> <p>To check which implementation will the generic function choose for a given type, use the <code class="docutils literal notranslate"><span class="pre">dispatch()</span></code> attribute:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">fun</span><span class="o">.</span><span class="n">dispatch</span><span class="p">(</span><span class="nb">float</span><span class="p">)</span> <span class="go"><function fun_num at 0x1035a2840></span> <span class="gp">>>> </span><span class="n">fun</span><span class="o">.</span><span class="n">dispatch</span><span class="p">(</span><span class="nb">dict</span><span class="p">)</span> <span class="c1"># note: default implementation</span> <span class="go"><function fun at 0x103fe0000></span> </pre></div> </div> <p>To access all registered implementations, use the read-only <code class="docutils literal notranslate"><span class="pre">registry</span></code> attribute:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">fun</span><span class="o">.</span><span class="n">registry</span><span class="o">.</span><span class="n">keys</span><span class="p">()</span> <span class="go">dict_keys([<class 'NoneType'>, <class 'int'>, <class 'object'>,</span> <span class="go"> <class 'decimal.Decimal'>, <class 'list'>,</span> <span class="go"> <class 'float'>])</span> <span class="gp">>>> </span><span class="n">fun</span><span class="o">.</span><span class="n">registry</span><span class="p">[</span><span class="nb">float</span><span class="p">]</span> <span class="go"><function fun_num at 0x1035a2840></span> <span class="gp">>>> </span><span class="n">fun</span><span class="o">.</span><span class="n">registry</span><span class="p">[</span><span class="nb">object</span><span class="p">]</span> <span class="go"><function fun at 0x103fe0000></span> </pre></div> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.7: </span>The <code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code> attribute supports using type annotations.</p> </div> </dd></dl> <dl class="function"> <dt id="functools.update_wrapper"> <code class="descclassname">functools.</code><code class="descname">update_wrapper</code><span class="sig-paren">(</span><em>wrapper</em>, <em>wrapped</em>, <em>assigned=WRAPPER_ASSIGNMENTS</em>, <em>updated=WRAPPER_UPDATES</em><span class="sig-paren">)</span><a class="headerlink" href="#functools.update_wrapper" title="Permalink to this definition">¶</a></dt> <dd><p>Update a <em>wrapper</em> function to look like the <em>wrapped</em> function. The optional arguments are tuples to specify which attributes of the original function are assigned directly to the matching attributes on the wrapper function and which attributes of the wrapper function are updated with the corresponding attributes from the original function. The default values for these arguments are the module level constants <code class="docutils literal notranslate"><span class="pre">WRAPPER_ASSIGNMENTS</span></code> (which assigns to the wrapper function’s <code class="docutils literal notranslate"><span class="pre">__module__</span></code>, <code class="docutils literal notranslate"><span class="pre">__name__</span></code>, <code class="docutils literal notranslate"><span class="pre">__qualname__</span></code>, <code class="docutils literal notranslate"><span class="pre">__annotations__</span></code> and <code class="docutils literal notranslate"><span class="pre">__doc__</span></code>, the documentation string) and <code class="docutils literal notranslate"><span class="pre">WRAPPER_UPDATES</span></code> (which updates the wrapper function’s <code class="docutils literal notranslate"><span class="pre">__dict__</span></code>, i.e. the instance dictionary).</p> <p>To allow access to the original function for introspection and other purposes (e.g. bypassing a caching decorator such as <a class="reference internal" href="#functools.lru_cache" title="functools.lru_cache"><code class="xref py py-func docutils literal notranslate"><span class="pre">lru_cache()</span></code></a>), this function automatically adds a <code class="docutils literal notranslate"><span class="pre">__wrapped__</span></code> attribute to the wrapper that refers to the function being wrapped.</p> <p>The main intended use for this function is in <a class="reference internal" href="../glossary.html#term-decorator"><span class="xref std std-term">decorator</span></a> functions which wrap the decorated function and return the wrapper. If the wrapper function is not updated, the metadata of the returned function will reflect the wrapper definition rather than the original function definition, which is typically less than helpful.</p> <p><a class="reference internal" href="#functools.update_wrapper" title="functools.update_wrapper"><code class="xref py py-func docutils literal notranslate"><span class="pre">update_wrapper()</span></code></a> may be used with callables other than functions. Any attributes named in <em>assigned</em> or <em>updated</em> that are missing from the object being wrapped are ignored (i.e. this function will not attempt to set them on the wrapper function). <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a> is still raised if the wrapper function itself is missing any attributes named in <em>updated</em>.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.2: </span>Automatic addition of the <code class="docutils literal notranslate"><span class="pre">__wrapped__</span></code> attribute.</p> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.2: </span>Copying of the <code class="docutils literal notranslate"><span class="pre">__annotations__</span></code> attribute by default.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.2: </span>Missing attributes no longer trigger an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a>.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.4: </span>The <code class="docutils literal notranslate"><span class="pre">__wrapped__</span></code> attribute now always refers to the wrapped function, even if that function defined a <code class="docutils literal notranslate"><span class="pre">__wrapped__</span></code> attribute. (see <a class="reference external" href="https://bugs.python.org/issue17482">bpo-17482</a>)</p> </div> </dd></dl> <dl class="function"> <dt id="functools.wraps"> <code class="descclassname">@</code><code class="descclassname">functools.</code><code class="descname">wraps</code><span class="sig-paren">(</span><em>wrapped</em>, <em>assigned=WRAPPER_ASSIGNMENTS</em>, <em>updated=WRAPPER_UPDATES</em><span class="sig-paren">)</span><a class="headerlink" href="#functools.wraps" title="Permalink to this definition">¶</a></dt> <dd><p>This is a convenience function for invoking <a class="reference internal" href="#functools.update_wrapper" title="functools.update_wrapper"><code class="xref py py-func docutils literal notranslate"><span class="pre">update_wrapper()</span></code></a> as a function decorator when defining a wrapper function. It is equivalent to <code class="docutils literal notranslate"><span class="pre">partial(update_wrapper,</span> <span class="pre">wrapped=wrapped,</span> <span class="pre">assigned=assigned,</span> <span class="pre">updated=updated)</span></code>. For example:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">functools</span> <span class="k">import</span> <span class="n">wraps</span> <span class="gp">>>> </span><span class="k">def</span> <span class="nf">my_decorator</span><span class="p">(</span><span class="n">f</span><span class="p">):</span> <span class="gp">... </span> <span class="nd">@wraps</span><span class="p">(</span><span class="n">f</span><span class="p">)</span> <span class="gp">... </span> <span class="k">def</span> <span class="nf">wrapper</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">):</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s1">'Calling decorated function'</span><span class="p">)</span> <span class="gp">... </span> <span class="k">return</span> <span class="n">f</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span> <span class="gp">... </span> <span class="k">return</span> <span class="n">wrapper</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="nd">@my_decorator</span> <span class="gp">... </span><span class="k">def</span> <span class="nf">example</span><span class="p">():</span> <span class="gp">... </span> <span class="sd">"""Docstring"""</span> <span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s1">'Called example function'</span><span class="p">)</span> <span class="gp">...</span> <span class="gp">>>> </span><span class="n">example</span><span class="p">()</span> <span class="go">Calling decorated function</span> <span class="go">Called example function</span> <span class="gp">>>> </span><span class="n">example</span><span class="o">.</span><span class="vm">__name__</span> <span class="go">'example'</span> <span class="gp">>>> </span><span class="n">example</span><span class="o">.</span><span class="vm">__doc__</span> <span class="go">'Docstring'</span> </pre></div> </div> <p>Without the use of this decorator factory, the name of the example function would have been <code class="docutils literal notranslate"><span class="pre">'wrapper'</span></code>, and the docstring of the original <code class="xref py py-func docutils literal notranslate"><span class="pre">example()</span></code> would have been lost.</p> </dd></dl> <div class="section" id="partial-objects"> <span id="id1"></span><h2><a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> Objects<a class="headerlink" href="#partial-objects" title="Permalink to this headline">¶</a></h2> <p><a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> objects are callable objects created by <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-func docutils literal notranslate"><span class="pre">partial()</span></code></a>. They have three read-only attributes:</p> <dl class="attribute"> <dt id="functools.partial.func"> <code class="descclassname">partial.</code><code class="descname">func</code><a class="headerlink" href="#functools.partial.func" title="Permalink to this definition">¶</a></dt> <dd><p>A callable object or function. Calls to the <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> object will be forwarded to <a class="reference internal" href="#functools.partial.func" title="functools.partial.func"><code class="xref py py-attr docutils literal notranslate"><span class="pre">func</span></code></a> with new arguments and keywords.</p> </dd></dl> <dl class="attribute"> <dt id="functools.partial.args"> <code class="descclassname">partial.</code><code class="descname">args</code><a class="headerlink" href="#functools.partial.args" title="Permalink to this definition">¶</a></dt> <dd><p>The leftmost positional arguments that will be prepended to the positional arguments provided to a <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> object call.</p> </dd></dl> <dl class="attribute"> <dt id="functools.partial.keywords"> <code class="descclassname">partial.</code><code class="descname">keywords</code><a class="headerlink" href="#functools.partial.keywords" title="Permalink to this definition">¶</a></dt> <dd><p>The keyword arguments that will be supplied when the <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> object is called.</p> </dd></dl> <p><a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> objects are like <code class="xref py py-class docutils literal notranslate"><span class="pre">function</span></code> objects in that they are callable, weak referencable, and can have attributes. There are some important differences. For instance, the <a class="reference internal" href="stdtypes.html#definition.__name__" title="definition.__name__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__name__</span></code></a> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">__doc__</span></code> attributes are not created automatically. Also, <a class="reference internal" href="#functools.partial" title="functools.partial"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code></a> objects defined in classes behave like static methods and do not transform into bound methods during instance attribute look-up.</p> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">functools</span></code> — Higher-order functions and operations on callable objects</a><ul> <li><a class="reference internal" href="#partial-objects"><code class="xref py py-class docutils literal notranslate"><span class="pre">partial</span></code> Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="itertools.html" title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">itertools</span></code> — Functions creating iterators for efficient looping</a></p> <h4>Next topic</h4> <p class="topless"><a href="operator.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">operator</span></code> — Standard operators as functions</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.7/Doc/library/functools.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="operator.html" title="operator — Standard operators as functions" >next</a> |</li> <li class="right" > <a href="itertools.html" title="itertools — Functions creating iterators for efficient looping" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <span class="language_switcher_placeholder">en</span> <span class="version_switcher_placeholder">3.7.4</span> <a href="../index.html">Documentation </a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="functional.html" >Functional Programming Modules</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 2001-2019, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on Jul 13, 2019. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.0.1. </div> </body> </html>