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<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 title="Miscellaneous operating system interfaces." class="reference external" href="../library/os.html#module-os"><tt class="xref 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 title="os.open" class="reference external" href="../library/os.html#os.open"><tt class="xref docutils literal"><span class="pre">os.open()</span></tt></a> from shadowing the built-in <a title="open" class="reference external" href="../library/functions.html#open"><tt class="xref docutils literal"><span class="pre">open()</span></tt></a> function which
operates much differently.</p>
<p id="index-1130">The built-in <a title="dir" class="reference external" href="../library/functions.html#dir"><tt class="xref docutils literal"><span class="pre">dir()</span></tt></a> and <a title="help" class="reference external" href="../library/functions.html#help"><tt class="xref docutils literal"><span class="pre">help()</span></tt></a> functions are useful as interactive
aids for working with large modules like <a title="Miscellaneous operating system interfaces." class="reference external" href="../library/os.html#module-os"><tt class="xref 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 title="High-level file operations, including copying." class="reference external" href="../library/shutil.html#module-shutil"><tt class="xref 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 title="Unix shell style pathname pattern expansion." class="reference external" href="../library/glob.html#module-glob"><tt class="xref 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 title="Access system-specific parameters and functions." class="reference external" href="../library/sys.html#module-sys"><tt class="xref 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 title="Portable parser for command line options; support both short and long option names." class="reference external" href="../library/getopt.html#module-getopt"><tt class="xref docutils literal"><span class="pre">getopt</span></tt></a> module processes <em>sys.argv</em> using the conventions of the Unix
<tt class="xref docutils literal"><span class="pre">getopt()</span></tt> function. More powerful and flexible command line processing is
provided by the <a title="Command-line option and argument parsing library." class="reference external" href="../library/argparse.html#module-argparse"><tt class="xref 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 title="Access system-specific parameters and functions." class="reference external" href="../library/sys.html#module-sys"><tt class="xref 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 title="Regular expression operations." class="reference external" href="../library/re.html#module-re"><tt class="xref 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 title="Mathematical functions (sin() etc.)." class="reference external" href="../library/math.html#module-math"><tt class="xref 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 title="Generate pseudo-random numbers with various common distributions." class="reference external" href="../library/random.html#module-random"><tt class="xref 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 title="Next generation URL opening library." class="reference external" href="../library/urllib2.html#module-urllib2"><tt class="xref docutils literal"><span class="pre">urllib2</span></tt></a> for retrieving data from urls
and <a title="SMTP protocol client (requires sockets)." class="reference external" href="../library/smtplib.html#module-smtplib"><tt class="xref 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 title="Basic date and time types." class="reference external" href="../library/datetime.html#module-datetime"><tt class="xref 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 title="Low-level interface to compression and decompression routines compatible with gzip." class="reference external" href="../library/zlib.html#module-zlib"><tt class="xref docutils literal"><span class="pre">zlib</span></tt></a>, <a title="Interfaces for gzip compression and decompression using file objects." class="reference external" href="../library/gzip.html#module-gzip"><tt class="xref docutils literal"><span class="pre">gzip</span></tt></a>, <a title="Interface to compression and decompression routines compatible with bzip2." class="reference external" href="../library/bz2.html#module-bz2"><tt class="xref docutils literal"><span class="pre">bz2</span></tt></a>, <a title="Read and write ZIP-format archive files." class="reference external" href="../library/zipfile.html#module-zipfile"><tt class="xref docutils literal"><span class="pre">zipfile</span></tt></a> and
<a title="Read and write tar-format archive files." class="reference external" href="../library/tarfile.html#module-tarfile"><tt class="xref 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 title="Measure the execution time of small code snippets." class="reference external" href="../library/timeit.html#module-timeit"><tt class="xref 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 title="Measure the execution time of small code snippets." class="reference external" href="../library/timeit.html#module-timeit"><tt class="xref docutils literal"><span class="pre">timeit</span></tt></a>‘s fine level of granularity, the <a title="Python source profiler." class="reference external" href="../library/profile.html#module-profile"><tt class="xref docutils literal"><span class="pre">profile</span></tt></a> and
<a title="Statistics object for use with the profiler." class="reference external" href="../library/profile.html#module-pstats"><tt class="xref 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 title="Test pieces of code within docstrings." class="reference external" href="../library/doctest.html#module-doctest"><tt class="xref 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 title="Unit testing framework for Python." class="reference external" href="../library/unittest.html#module-unittest"><tt class="xref docutils literal"><span class="pre">unittest</span></tt></a> module is not as effortless as the <a title="Test pieces of code within docstrings." class="reference external" href="../library/doctest.html#module-doctest"><tt class="xref 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="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="p">[])</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 title="XML-RPC client access." class="reference external" href="../library/xmlrpclib.html#module-xmlrpclib"><tt class="xref docutils literal"><span class="pre">xmlrpclib</span></tt></a> and <a title="Basic XML-RPC server implementation." class="reference external" href="../library/simplexmlrpcserver.html#module-SimpleXMLRPCServer"><tt class="xref 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 title="Package supporting the parsing, manipulating, and generating email messages, including MIME documents." class="reference external" href="../library/email.html#module-email"><tt class="xref 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 title="SMTP protocol client (requires sockets)." class="reference external" href="../library/smtplib.html#module-smtplib"><tt class="xref docutils literal"><span class="pre">smtplib</span></tt></a> and
<a title="POP3 protocol client (requires sockets)." class="reference external" href="../library/poplib.html#module-poplib"><tt class="xref 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 title="Document Object Model API for Python." class="reference external" href="../library/xml.dom.html#module-xml.dom"><tt class="xref docutils literal"><span class="pre">xml.dom</span></tt></a> and <a title="Package containing SAX2 base classes and convenience functions." class="reference external" href="../library/xml.sax.html#module-xml.sax"><tt class="xref docutils literal"><span class="pre">xml.sax</span></tt></a> packages provide robust support for
parsing this popular data interchange format. Likewise, the <a title="Write and read tabular data to and from delimited files." class="reference external" href="../library/csv.html#module-csv"><tt class="xref 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 title="Multilingual internationalization services." class="reference external" href="../library/gettext.html#module-gettext"><tt class="xref docutils literal"><span class="pre">gettext</span></tt></a>, <a title="Internationalization services." class="reference external" href="../library/locale.html#module-locale"><tt class="xref docutils literal"><span class="pre">locale</span></tt></a>, and the <a title="Encode and decode data and streams." class="reference external" href="../library/codecs.html#module-codecs"><tt class="xref docutils literal"><span class="pre">codecs</span></tt></a> package.</li>
</ul>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">10. Brief Tour of the Standard Library</a><ul>
<li><a class="reference external" href="#operating-system-interface">10.1. Operating System Interface</a></li>
<li><a class="reference external" href="#file-wildcards">10.2. File Wildcards</a></li>
<li><a class="reference external" href="#command-line-arguments">10.3. Command Line Arguments</a></li>
<li><a class="reference external" href="#error-output-redirection-and-program-termination">10.4. Error Output Redirection and Program Termination</a></li>
<li><a class="reference external" href="#string-pattern-matching">10.5. String Pattern Matching</a></li>
<li><a class="reference external" href="#mathematics">10.6. Mathematics</a></li>
<li><a class="reference external" href="#internet-access">10.7. Internet Access</a></li>
<li><a class="reference external" href="#dates-and-times">10.8. Dates and Times</a></li>
<li><a class="reference external" href="#data-compression">10.9. Data Compression</a></li>
<li><a class="reference external" href="#performance-measurement">10.10. Performance Measurement</a></li>
<li><a class="reference external" href="#quality-control">10.11. Quality Control</a></li>
<li><a class="reference external" href="#batteries-included">10.12. Batteries Included</a></li>
</ul>
</li>
</ul>
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