Edit File: stdlib.html
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Brief Tour of the Standard Library — Python 2.7.5 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.7.5', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </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/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.5 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python 2.7.5 documentation" href="../index.html" /> <link rel="up" title="The Python Tutorial" href="index.html" /> <link rel="next" title="11. Brief Tour of the Standard Library – Part II" href="stdlib2.html" /> <link rel="prev" title="9. Classes" href="classes.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head> <body> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="stdlib2.html" title="11. Brief Tour of the Standard Library – Part II" accesskey="N">next</a> |</li> <li class="right" > <a href="classes.html" title="9. Classes" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="http://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.5 documentation</a> » </li> <li><a href="index.html" accesskey="U">The Python Tutorial</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="brief-tour-of-the-standard-library"> <span id="tut-brieftour"></span><h1>10. Brief Tour of the Standard Library<a class="headerlink" href="#brief-tour-of-the-standard-library" title="Permalink to this headline">¶</a></h1> <div class="section" id="operating-system-interface"> <span id="tut-os-interface"></span><h2>10.1. Operating System Interface<a class="headerlink" href="#operating-system-interface" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><tt class="xref py py-mod docutils literal"><span class="pre">os</span></tt></a> module provides dozens of functions for interacting with the operating system:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">os</span> <span class="gp">>>> </span><span class="n">os</span><span class="o">.</span><span class="n">getcwd</span><span class="p">()</span> <span class="c"># Return the current working directory</span> <span class="go">'C:\\Python26'</span> <span class="gp">>>> </span><span class="n">os</span><span class="o">.</span><span class="n">chdir</span><span class="p">(</span><span class="s">'/server/accesslogs'</span><span class="p">)</span> <span class="c"># Change current working directory</span> <span class="gp">>>> </span><span class="n">os</span><span class="o">.</span><span class="n">system</span><span class="p">(</span><span class="s">'mkdir today'</span><span class="p">)</span> <span class="c"># Run the command mkdir in the system shell</span> <span class="go">0</span> </pre></div> </div> <p>Be sure to use the <tt class="docutils literal"><span class="pre">import</span> <span class="pre">os</span></tt> style instead of <tt class="docutils literal"><span class="pre">from</span> <span class="pre">os</span> <span class="pre">import</span> <span class="pre">*</span></tt>. This will keep <a class="reference internal" href="../library/os.html#os.open" title="os.open"><tt class="xref py py-func docutils literal"><span class="pre">os.open()</span></tt></a> from shadowing the built-in <a class="reference internal" href="../library/functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function which operates much differently.</p> <p id="index-0">The built-in <a class="reference internal" href="../library/functions.html#dir" title="dir"><tt class="xref py py-func docutils literal"><span class="pre">dir()</span></tt></a> and <a class="reference internal" href="../library/functions.html#help" title="help"><tt class="xref py py-func docutils literal"><span class="pre">help()</span></tt></a> functions are useful as interactive aids for working with large modules like <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><tt class="xref py py-mod docutils literal"><span class="pre">os</span></tt></a>:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">os</span> <span class="gp">>>> </span><span class="nb">dir</span><span class="p">(</span><span class="n">os</span><span class="p">)</span> <span class="go"><returns a list of all module functions></span> <span class="gp">>>> </span><span class="n">help</span><span class="p">(</span><span class="n">os</span><span class="p">)</span> <span class="go"><returns an extensive manual page created from the module's docstrings></span> </pre></div> </div> <p>For daily file and directory management tasks, the <a class="reference internal" href="../library/shutil.html#module-shutil" title="shutil: High-level file operations, including copying."><tt class="xref py py-mod docutils literal"><span class="pre">shutil</span></tt></a> module provides a higher level interface that is easier to use:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">shutil</span> <span class="gp">>>> </span><span class="n">shutil</span><span class="o">.</span><span class="n">copyfile</span><span class="p">(</span><span class="s">'data.db'</span><span class="p">,</span> <span class="s">'archive.db'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">shutil</span><span class="o">.</span><span class="n">move</span><span class="p">(</span><span class="s">'/build/executables'</span><span class="p">,</span> <span class="s">'installdir'</span><span class="p">)</span> </pre></div> </div> </div> <div class="section" id="file-wildcards"> <span id="tut-file-wildcards"></span><h2>10.2. File Wildcards<a class="headerlink" href="#file-wildcards" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="../library/glob.html#module-glob" title="glob: Unix shell style pathname pattern expansion."><tt class="xref py py-mod docutils literal"><span class="pre">glob</span></tt></a> module provides a function for making file lists from directory wildcard searches:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">glob</span> <span class="gp">>>> </span><span class="n">glob</span><span class="o">.</span><span class="n">glob</span><span class="p">(</span><span class="s">'*.py'</span><span class="p">)</span> <span class="go">['primes.py', 'random.py', 'quote.py']</span> </pre></div> </div> </div> <div class="section" id="command-line-arguments"> <span id="tut-command-line-arguments"></span><h2>10.3. Command Line Arguments<a class="headerlink" href="#command-line-arguments" title="Permalink to this headline">¶</a></h2> <p>Common utility scripts often need to process command line arguments. These arguments are stored in the <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><tt class="xref py py-mod docutils literal"><span class="pre">sys</span></tt></a> module’s <em>argv</em> attribute as a list. For instance the following output results from running <tt class="docutils literal"><span class="pre">python</span> <span class="pre">demo.py</span> <span class="pre">one</span> <span class="pre">two</span> <span class="pre">three</span></tt> at the command line:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">sys</span> <span class="gp">>>> </span><span class="k">print</span> <span class="n">sys</span><span class="o">.</span><span class="n">argv</span> <span class="go">['demo.py', 'one', 'two', 'three']</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/getopt.html#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><tt class="xref py py-mod docutils literal"><span class="pre">getopt</span></tt></a> module processes <em>sys.argv</em> using the conventions of the Unix <a class="reference internal" href="../library/getopt.html#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><tt class="xref py py-func docutils literal"><span class="pre">getopt()</span></tt></a> function. More powerful and flexible command line processing is provided by the <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><tt class="xref py py-mod docutils literal"><span class="pre">argparse</span></tt></a> module.</p> </div> <div class="section" id="error-output-redirection-and-program-termination"> <span id="tut-stderr"></span><h2>10.4. Error Output Redirection and Program Termination<a class="headerlink" href="#error-output-redirection-and-program-termination" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><tt class="xref py py-mod docutils literal"><span class="pre">sys</span></tt></a> module also has attributes for <em>stdin</em>, <em>stdout</em>, and <em>stderr</em>. The latter is useful for emitting warnings and error messages to make them visible even when <em>stdout</em> has been redirected:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">'Warning, log file not found starting a new one</span><span class="se">\n</span><span class="s">'</span><span class="p">)</span> <span class="go">Warning, log file not found starting a new one</span> </pre></div> </div> <p>The most direct way to terminate a script is to use <tt class="docutils literal"><span class="pre">sys.exit()</span></tt>.</p> </div> <div class="section" id="string-pattern-matching"> <span id="tut-string-pattern-matching"></span><h2>10.5. String Pattern Matching<a class="headerlink" href="#string-pattern-matching" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="../library/re.html#module-re" title="re: Regular expression operations."><tt class="xref py py-mod docutils literal"><span class="pre">re</span></tt></a> module provides regular expression tools for advanced string processing. For complex matching and manipulation, regular expressions offer succinct, optimized solutions:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">re</span> <span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="s">r'\bf[a-z]*'</span><span class="p">,</span> <span class="s">'which foot or hand fell fastest'</span><span class="p">)</span> <span class="go">['foot', 'fell', 'fastest']</span> <span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="s">r'(\b[a-z]+) \1'</span><span class="p">,</span> <span class="s">r'\1'</span><span class="p">,</span> <span class="s">'cat in the the hat'</span><span class="p">)</span> <span class="go">'cat in the hat'</span> </pre></div> </div> <p>When only simple capabilities are needed, string methods are preferred because they are easier to read and debug:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="s">'tea for too'</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s">'too'</span><span class="p">,</span> <span class="s">'two'</span><span class="p">)</span> <span class="go">'tea for two'</span> </pre></div> </div> </div> <div class="section" id="mathematics"> <span id="tut-mathematics"></span><h2>10.6. Mathematics<a class="headerlink" href="#mathematics" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><tt class="xref py py-mod docutils literal"><span class="pre">math</span></tt></a> module gives access to the underlying C library functions for floating point math:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">math</span> <span class="gp">>>> </span><span class="n">math</span><span class="o">.</span><span class="n">cos</span><span class="p">(</span><span class="n">math</span><span class="o">.</span><span class="n">pi</span> <span class="o">/</span> <span class="mf">4.0</span><span class="p">)</span> <span class="go">0.70710678118654757</span> <span class="gp">>>> </span><span class="n">math</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="mi">1024</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span> <span class="go">10.0</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/random.html#module-random" title="random: Generate pseudo-random numbers with various common distributions."><tt class="xref py py-mod docutils literal"><span class="pre">random</span></tt></a> module provides tools for making random selections:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">random</span> <span class="gp">>>> </span><span class="n">random</span><span class="o">.</span><span class="n">choice</span><span class="p">([</span><span class="s">'apple'</span><span class="p">,</span> <span class="s">'pear'</span><span class="p">,</span> <span class="s">'banana'</span><span class="p">])</span> <span class="go">'apple'</span> <span class="gp">>>> </span><span class="n">random</span><span class="o">.</span><span class="n">sample</span><span class="p">(</span><span class="nb">xrange</span><span class="p">(</span><span class="mi">100</span><span class="p">),</span> <span class="mi">10</span><span class="p">)</span> <span class="c"># sampling without replacement</span> <span class="go">[30, 83, 16, 4, 8, 81, 41, 50, 18, 33]</span> <span class="gp">>>> </span><span class="n">random</span><span class="o">.</span><span class="n">random</span><span class="p">()</span> <span class="c"># random float</span> <span class="go">0.17970987693706186</span> <span class="gp">>>> </span><span class="n">random</span><span class="o">.</span><span class="n">randrange</span><span class="p">(</span><span class="mi">6</span><span class="p">)</span> <span class="c"># random integer chosen from range(6)</span> <span class="go">4</span> </pre></div> </div> </div> <div class="section" id="internet-access"> <span id="tut-internet-access"></span><h2>10.7. Internet Access<a class="headerlink" href="#internet-access" title="Permalink to this headline">¶</a></h2> <p>There are a number of modules for accessing the internet and processing internet protocols. Two of the simplest are <a class="reference internal" href="../library/urllib2.html#module-urllib2" title="urllib2: Next generation URL opening library."><tt class="xref py py-mod docutils literal"><span class="pre">urllib2</span></tt></a> for retrieving data from URLs and <a class="reference internal" href="../library/smtplib.html#module-smtplib" title="smtplib: SMTP protocol client (requires sockets)."><tt class="xref py py-mod docutils literal"><span class="pre">smtplib</span></tt></a> for sending mail:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">urllib2</span> <span class="gp">>>> </span><span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">urllib2</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="s">'http://tycho.usno.navy.mil/cgi-bin/timer.pl'</span><span class="p">):</span> <span class="gp">... </span> <span class="k">if</span> <span class="s">'EST'</span> <span class="ow">in</span> <span class="n">line</span> <span class="ow">or</span> <span class="s">'EDT'</span> <span class="ow">in</span> <span class="n">line</span><span class="p">:</span> <span class="c"># look for Eastern Time</span> <span class="gp">... </span> <span class="k">print</span> <span class="n">line</span> <span class="go"><BR>Nov. 25, 09:43:32 PM EST</span> <span class="gp">>>> </span><span class="kn">import</span> <span class="nn">smtplib</span> <span class="gp">>>> </span><span class="n">server</span> <span class="o">=</span> <span class="n">smtplib</span><span class="o">.</span><span class="n">SMTP</span><span class="p">(</span><span class="s">'localhost'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">server</span><span class="o">.</span><span class="n">sendmail</span><span class="p">(</span><span class="s">'soothsayer@example.org'</span><span class="p">,</span> <span class="s">'jcaesar@example.org'</span><span class="p">,</span> <span class="gp">... </span><span class="sd">"""To: jcaesar@example.org</span> <span class="gp">... </span><span class="sd">From: soothsayer@example.org</span> <span class="gp">...</span><span class="sd"></span> <span class="gp">... </span><span class="sd">Beware the Ides of March.</span> <span class="gp">... </span><span class="sd">"""</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">server</span><span class="o">.</span><span class="n">quit</span><span class="p">()</span> </pre></div> </div> <p>(Note that the second example needs a mailserver running on localhost.)</p> </div> <div class="section" id="dates-and-times"> <span id="tut-dates-and-times"></span><h2>10.8. Dates and Times<a class="headerlink" href="#dates-and-times" title="Permalink to this headline">¶</a></h2> <p>The <a class="reference internal" href="../library/datetime.html#module-datetime" title="datetime: Basic date and time types."><tt class="xref py py-mod docutils literal"><span class="pre">datetime</span></tt></a> module supplies classes for manipulating dates and times in both simple and complex ways. While date and time arithmetic is supported, the focus of the implementation is on efficient member extraction for output formatting and manipulation. The module also supports objects that are timezone aware.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="c"># dates are easily constructed and formatted</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">datetime</span> <span class="kn">import</span> <span class="n">date</span> <span class="gp">>>> </span><span class="n">now</span> <span class="o">=</span> <span class="n">date</span><span class="o">.</span><span class="n">today</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">now</span> <span class="go">datetime.date(2003, 12, 2)</span> <span class="gp">>>> </span><span class="n">now</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s">"%m-</span><span class="si">%d</span><span class="s">-%y. </span><span class="si">%d</span><span class="s"> %b %Y is a %A on the </span><span class="si">%d</span><span class="s"> day of %B."</span><span class="p">)</span> <span class="go">'12-02-03. 02 Dec 2003 is a Tuesday on the 02 day of December.'</span> <span class="gp">>>> </span><span class="c"># dates support calendar arithmetic</span> <span class="gp">>>> </span><span class="n">birthday</span> <span class="o">=</span> <span class="n">date</span><span class="p">(</span><span class="mi">1964</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">31</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">age</span> <span class="o">=</span> <span class="n">now</span> <span class="o">-</span> <span class="n">birthday</span> <span class="gp">>>> </span><span class="n">age</span><span class="o">.</span><span class="n">days</span> <span class="go">14368</span> </pre></div> </div> </div> <div class="section" id="data-compression"> <span id="tut-data-compression"></span><h2>10.9. Data Compression<a class="headerlink" href="#data-compression" title="Permalink to this headline">¶</a></h2> <p>Common data archiving and compression formats are directly supported by modules including: <a class="reference internal" href="../library/zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><tt class="xref py py-mod docutils literal"><span class="pre">zlib</span></tt></a>, <a class="reference internal" href="../library/gzip.html#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><tt class="xref py py-mod docutils literal"><span class="pre">gzip</span></tt></a>, <a class="reference internal" href="../library/bz2.html#module-bz2" title="bz2: Interface to compression and decompression routines compatible with bzip2."><tt class="xref py py-mod docutils literal"><span class="pre">bz2</span></tt></a>, <a class="reference internal" href="../library/zipfile.html#module-zipfile" title="zipfile: Read and write ZIP-format archive files."><tt class="xref py py-mod docutils literal"><span class="pre">zipfile</span></tt></a> and <a class="reference internal" href="../library/tarfile.html#module-tarfile" title="tarfile: Read and write tar-format archive files."><tt class="xref py py-mod docutils literal"><span class="pre">tarfile</span></tt></a>.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">zlib</span> <span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s">'witch which has which witches wrist watch'</span> <span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="go">41</span> <span class="gp">>>> </span><span class="n">t</span> <span class="o">=</span> <span class="n">zlib</span><span class="o">.</span><span class="n">compress</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="go">37</span> <span class="gp">>>> </span><span class="n">zlib</span><span class="o">.</span><span class="n">decompress</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="go">'witch which has which witches wrist watch'</span> <span class="gp">>>> </span><span class="n">zlib</span><span class="o">.</span><span class="n">crc32</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="go">226805979</span> </pre></div> </div> </div> <div class="section" id="performance-measurement"> <span id="tut-performance-measurement"></span><h2>10.10. Performance Measurement<a class="headerlink" href="#performance-measurement" title="Permalink to this headline">¶</a></h2> <p>Some Python users develop a deep interest in knowing the relative performance of different approaches to the same problem. Python provides a measurement tool that answers those questions immediately.</p> <p>For example, it may be tempting to use the tuple packing and unpacking feature instead of the traditional approach to swapping arguments. The <a class="reference internal" href="../library/timeit.html#module-timeit" title="timeit: Measure the execution time of small code snippets."><tt class="xref py py-mod docutils literal"><span class="pre">timeit</span></tt></a> module quickly demonstrates a modest performance advantage:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">timeit</span> <span class="kn">import</span> <span class="n">Timer</span> <span class="gp">>>> </span><span class="n">Timer</span><span class="p">(</span><span class="s">'t=a; a=b; b=t'</span><span class="p">,</span> <span class="s">'a=1; b=2'</span><span class="p">)</span><span class="o">.</span><span class="n">timeit</span><span class="p">()</span> <span class="go">0.57535828626024577</span> <span class="gp">>>> </span><span class="n">Timer</span><span class="p">(</span><span class="s">'a,b = b,a'</span><span class="p">,</span> <span class="s">'a=1; b=2'</span><span class="p">)</span><span class="o">.</span><span class="n">timeit</span><span class="p">()</span> <span class="go">0.54962537085770791</span> </pre></div> </div> <p>In contrast to <a class="reference internal" href="../library/timeit.html#module-timeit" title="timeit: Measure the execution time of small code snippets."><tt class="xref py py-mod docutils literal"><span class="pre">timeit</span></tt></a>‘s fine level of granularity, the <a class="reference internal" href="../library/profile.html#module-profile" title="profile: Python source profiler."><tt class="xref py py-mod docutils literal"><span class="pre">profile</span></tt></a> and <a class="reference internal" href="../library/profile.html#module-pstats" title="pstats: Statistics object for use with the profiler."><tt class="xref py py-mod docutils literal"><span class="pre">pstats</span></tt></a> modules provide tools for identifying time critical sections in larger blocks of code.</p> </div> <div class="section" id="quality-control"> <span id="tut-quality-control"></span><h2>10.11. Quality Control<a class="headerlink" href="#quality-control" title="Permalink to this headline">¶</a></h2> <p>One approach for developing high quality software is to write tests for each function as it is developed and to run those tests frequently during the development process.</p> <p>The <a class="reference internal" href="../library/doctest.html#module-doctest" title="doctest: Test pieces of code within docstrings."><tt class="xref py py-mod docutils literal"><span class="pre">doctest</span></tt></a> module provides a tool for scanning a module and validating tests embedded in a program’s docstrings. Test construction is as simple as cutting-and-pasting a typical call along with its results into the docstring. This improves the documentation by providing the user with an example and it allows the doctest module to make sure the code remains true to the documentation:</p> <div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">average</span><span class="p">(</span><span class="n">values</span><span class="p">):</span> <span class="sd">"""Computes the arithmetic mean of a list of numbers.</span> <span class="sd"> >>> print average([20, 30, 70])</span> <span class="sd"> 40.0</span> <span class="sd"> """</span> <span class="k">return</span> <span class="nb">sum</span><span class="p">(</span><span class="n">values</span><span class="p">,</span> <span class="mf">0.0</span><span class="p">)</span> <span class="o">/</span> <span class="nb">len</span><span class="p">(</span><span class="n">values</span><span class="p">)</span> <span class="kn">import</span> <span class="nn">doctest</span> <span class="n">doctest</span><span class="o">.</span><span class="n">testmod</span><span class="p">()</span> <span class="c"># automatically validate the embedded tests</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><tt class="xref py py-mod docutils literal"><span class="pre">unittest</span></tt></a> module is not as effortless as the <a class="reference internal" href="../library/doctest.html#module-doctest" title="doctest: Test pieces of code within docstrings."><tt class="xref py py-mod docutils literal"><span class="pre">doctest</span></tt></a> module, but it allows a more comprehensive set of tests to be maintained in a separate file:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">unittest</span> <span class="k">class</span> <span class="nc">TestStatisticalFunctions</span><span class="p">(</span><span class="n">unittest</span><span class="o">.</span><span class="n">TestCase</span><span class="p">):</span> <span class="k">def</span> <span class="nf">test_average</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">assertEqual</span><span class="p">(</span><span class="n">average</span><span class="p">([</span><span class="mi">20</span><span class="p">,</span> <span class="mi">30</span><span class="p">,</span> <span class="mi">70</span><span class="p">]),</span> <span class="mf">40.0</span><span class="p">)</span> <span class="bp">self</span><span class="o">.</span><span class="n">assertEqual</span><span class="p">(</span><span class="nb">round</span><span class="p">(</span><span class="n">average</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">7</span><span class="p">]),</span> <span class="mi">1</span><span class="p">),</span> <span class="mf">4.3</span><span class="p">)</span> <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> <span class="n">average</span><span class="p">([])</span> <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">TypeError</span><span class="p">):</span> <span class="n">average</span><span class="p">(</span><span class="mi">20</span><span class="p">,</span> <span class="mi">30</span><span class="p">,</span> <span class="mi">70</span><span class="p">)</span> <span class="n">unittest</span><span class="o">.</span><span class="n">main</span><span class="p">()</span> <span class="c"># Calling from the command line invokes all tests</span> </pre></div> </div> </div> <div class="section" id="batteries-included"> <span id="tut-batteries-included"></span><h2>10.12. Batteries Included<a class="headerlink" href="#batteries-included" title="Permalink to this headline">¶</a></h2> <p>Python has a “batteries included” philosophy. This is best seen through the sophisticated and robust capabilities of its larger packages. For example:</p> <ul class="simple"> <li>The <a class="reference internal" href="../library/xmlrpclib.html#module-xmlrpclib" title="xmlrpclib: XML-RPC client access."><tt class="xref py py-mod docutils literal"><span class="pre">xmlrpclib</span></tt></a> and <a class="reference internal" href="../library/simplexmlrpcserver.html#module-SimpleXMLRPCServer" title="SimpleXMLRPCServer: Basic XML-RPC server implementation."><tt class="xref py py-mod docutils literal"><span class="pre">SimpleXMLRPCServer</span></tt></a> modules make implementing remote procedure calls into an almost trivial task. Despite the modules names, no direct knowledge or handling of XML is needed.</li> <li>The <a class="reference internal" href="../library/email.html#module-email" title="email: Package supporting the parsing, manipulating, and generating email messages, including MIME documents."><tt class="xref py py-mod docutils literal"><span class="pre">email</span></tt></a> package is a library for managing email messages, including MIME and other RFC 2822-based message documents. Unlike <a class="reference internal" href="../library/smtplib.html#module-smtplib" title="smtplib: SMTP protocol client (requires sockets)."><tt class="xref py py-mod docutils literal"><span class="pre">smtplib</span></tt></a> and <a class="reference internal" href="../library/poplib.html#module-poplib" title="poplib: POP3 protocol client (requires sockets)."><tt class="xref py py-mod docutils literal"><span class="pre">poplib</span></tt></a> which actually send and receive messages, the email package has a complete toolset for building or decoding complex message structures (including attachments) and for implementing internet encoding and header protocols.</li> <li>The <a class="reference internal" href="../library/xml.dom.html#module-xml.dom" title="xml.dom: Document Object Model API for Python."><tt class="xref py py-mod docutils literal"><span class="pre">xml.dom</span></tt></a> and <a class="reference internal" href="../library/xml.sax.html#module-xml.sax" title="xml.sax: Package containing SAX2 base classes and convenience functions."><tt class="xref py py-mod docutils literal"><span class="pre">xml.sax</span></tt></a> packages provide robust support for parsing this popular data interchange format. Likewise, the <a class="reference internal" href="../library/csv.html#module-csv" title="csv: Write and read tabular data to and from delimited files."><tt class="xref py py-mod docutils literal"><span class="pre">csv</span></tt></a> module supports direct reads and writes in a common database format. Together, these modules and packages greatly simplify data interchange between Python applications and other tools.</li> <li>Internationalization is supported by a number of modules including <a class="reference internal" href="../library/gettext.html#module-gettext" title="gettext: Multilingual internationalization services."><tt class="xref py py-mod docutils literal"><span class="pre">gettext</span></tt></a>, <a class="reference internal" href="../library/locale.html#module-locale" title="locale: Internationalization services."><tt class="xref py py-mod docutils literal"><span class="pre">locale</span></tt></a>, and the <a class="reference internal" href="../library/codecs.html#module-codecs" title="codecs: Encode and decode data and streams."><tt class="xref py py-mod docutils literal"><span class="pre">codecs</span></tt></a> package.</li> </ul> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">10. Brief Tour of the Standard Library</a><ul> <li><a class="reference internal" href="#operating-system-interface">10.1. Operating System Interface</a></li> <li><a class="reference internal" href="#file-wildcards">10.2. File Wildcards</a></li> <li><a class="reference internal" href="#command-line-arguments">10.3. Command Line Arguments</a></li> <li><a class="reference internal" href="#error-output-redirection-and-program-termination">10.4. Error Output Redirection and Program Termination</a></li> <li><a class="reference internal" href="#string-pattern-matching">10.5. String Pattern Matching</a></li> <li><a class="reference internal" href="#mathematics">10.6. Mathematics</a></li> <li><a class="reference internal" href="#internet-access">10.7. Internet Access</a></li> <li><a class="reference internal" href="#dates-and-times">10.8. Dates and Times</a></li> <li><a class="reference internal" href="#data-compression">10.9. Data Compression</a></li> <li><a class="reference internal" href="#performance-measurement">10.10. Performance Measurement</a></li> <li><a class="reference internal" href="#quality-control">10.11. Quality Control</a></li> <li><a class="reference internal" href="#batteries-included">10.12. Batteries Included</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="classes.html" title="previous chapter">9. Classes</a></p> <h4>Next topic</h4> <p class="topless"><a href="stdlib2.html" title="next chapter">11. 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