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<li><a class="reference internal" href="#">10. Brief Tour of the Standard Library</a><ul>
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<li><a class="reference internal" href="#operating-system-interface">10.1. Operating System Interface</a></li>
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<section id="brief-tour-of-the-standard-library">
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<span id="tut-brieftour"></span><h1><span class="section-number">10. </span>Brief Tour of the Standard Library<a class="headerlink" href="#brief-tour-of-the-standard-library" title="Link to this heading">¶</a></h1>
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<section id="operating-system-interface">
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<span id="tut-os-interface"></span><h2><span class="section-number">10.1. </span>Operating System Interface<a class="headerlink" href="#operating-system-interface" title="Link to this heading">¶</a></h2>
|
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<p>The <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module provides dozens of functions for interacting with the
|
||
operating system:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </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="c1"># Return the current working directory</span>
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||
<span class="go">'C:\\Python313'</span>
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||
<span class="gp">>>> </span><span class="n">os</span><span class="o">.</span><span class="n">chdir</span><span class="p">(</span><span class="s1">'/server/accesslogs'</span><span class="p">)</span> <span class="c1"># 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="s1">'mkdir today'</span><span class="p">)</span> <span class="c1"># Run the command mkdir in the system shell</span>
|
||
<span class="go">0</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Be sure to use the <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">os</span></code> style instead of <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">os</span> <span class="pre">import</span> <span class="pre">*</span></code>. This
|
||
will keep <a class="reference internal" href="../library/os.html#os.open" title="os.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.open()</span></code></a> from shadowing the built-in <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></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"><code class="xref py py-func docutils literal notranslate"><span class="pre">dir()</span></code></a> and <a class="reference internal" href="../library/functions.html#help" title="help"><code class="xref py py-func docutils literal notranslate"><span class="pre">help()</span></code></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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a>:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">os</span>
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||
<span class="gp">>>> </span><span class="nb">dir</span><span class="p">(</span><span class="n">os</span><span class="p">)</span>
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||
<span class="go"><returns a list of all module functions></span>
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||
<span class="gp">>>> </span><span class="n">help</span><span class="p">(</span><span class="n">os</span><span class="p">)</span>
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||
<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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shutil</span></code></a> module provides
|
||
a higher level interface that is easier to use:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">shutil</span>
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||
<span class="gp">>>> </span><span class="n">shutil</span><span class="o">.</span><span class="n">copyfile</span><span class="p">(</span><span class="s1">'data.db'</span><span class="p">,</span> <span class="s1">'archive.db'</span><span class="p">)</span>
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<span class="go">'archive.db'</span>
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<span class="gp">>>> </span><span class="n">shutil</span><span class="o">.</span><span class="n">move</span><span class="p">(</span><span class="s1">'/build/executables'</span><span class="p">,</span> <span class="s1">'installdir'</span><span class="p">)</span>
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<span class="go">'installdir'</span>
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||
</pre></div>
|
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</div>
|
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</section>
|
||
<section id="file-wildcards">
|
||
<span id="tut-file-wildcards"></span><h2><span class="section-number">10.2. </span>File Wildcards<a class="headerlink" href="#file-wildcards" title="Link to this heading">¶</a></h2>
|
||
<p>The <a class="reference internal" href="../library/glob.html#module-glob" title="glob: Unix shell style pathname pattern expansion."><code class="xref py py-mod docutils literal notranslate"><span class="pre">glob</span></code></a> module provides a function for making file lists from directory
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||
wildcard searches:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </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="s1">'*.py'</span><span class="p">)</span>
|
||
<span class="go">['primes.py', 'random.py', 'quote.py']</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="command-line-arguments">
|
||
<span id="tut-command-line-arguments"></span><h2><span class="section-number">10.3. </span>Command Line Arguments<a class="headerlink" href="#command-line-arguments" title="Link to this heading">¶</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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></a> module’s <em>argv</em> attribute as a list. For
|
||
instance, let’s take the following <code class="file docutils literal notranslate"><span class="pre">demo.py</span></code> file:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># File demo.py</span>
|
||
<span class="kn">import</span><span class="w"> </span><span class="nn">sys</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Here is the output from running <code class="docutils literal notranslate"><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></code> at the command
|
||
line:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="s1">'demo.py'</span><span class="p">,</span> <span class="s1">'one'</span><span class="p">,</span> <span class="s1">'two'</span><span class="p">,</span> <span class="s1">'three'</span><span class="p">]</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate"><span class="pre">argparse</span></code></a> module provides a more sophisticated mechanism to process
|
||
command line arguments. The following script extracts one or more filenames
|
||
and an optional number of lines to be displayed:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">argparse</span>
|
||
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||
<span class="n">parser</span> <span class="o">=</span> <span class="n">argparse</span><span class="o">.</span><span class="n">ArgumentParser</span><span class="p">(</span>
|
||
<span class="n">prog</span><span class="o">=</span><span class="s1">'top'</span><span class="p">,</span>
|
||
<span class="n">description</span><span class="o">=</span><span class="s1">'Show top lines from each file'</span><span class="p">)</span>
|
||
<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s1">'filenames'</span><span class="p">,</span> <span class="n">nargs</span><span class="o">=</span><span class="s1">'+'</span><span class="p">)</span>
|
||
<span class="n">parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span><span class="s1">'-l'</span><span class="p">,</span> <span class="s1">'--lines'</span><span class="p">,</span> <span class="nb">type</span><span class="o">=</span><span class="nb">int</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="mi">10</span><span class="p">)</span>
|
||
<span class="n">args</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">()</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="n">args</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>When run at the command line with <code class="docutils literal notranslate"><span class="pre">python</span> <span class="pre">top.py</span> <span class="pre">--lines=5</span> <span class="pre">alpha.txt</span>
|
||
<span class="pre">beta.txt</span></code>, the script sets <code class="docutils literal notranslate"><span class="pre">args.lines</span></code> to <code class="docutils literal notranslate"><span class="pre">5</span></code> and <code class="docutils literal notranslate"><span class="pre">args.filenames</span></code>
|
||
to <code class="docutils literal notranslate"><span class="pre">['alpha.txt',</span> <span class="pre">'beta.txt']</span></code>.</p>
|
||
</section>
|
||
<section id="error-output-redirection-and-program-termination">
|
||
<span id="tut-stderr"></span><h2><span class="section-number">10.4. </span>Error Output Redirection and Program Termination<a class="headerlink" href="#error-output-redirection-and-program-termination" title="Link to this heading">¶</a></h2>
|
||
<p>The <a class="reference internal" href="../library/sys.html#module-sys" title="sys: Access system-specific parameters and functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sys</span></code></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-python3 notranslate"><div class="highlight"><pre><span></span><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="s1">'Warning, log file not found starting a new one</span><span class="se">\n</span><span class="s1">'</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 <code class="docutils literal notranslate"><span class="pre">sys.exit()</span></code>.</p>
|
||
</section>
|
||
<section id="string-pattern-matching">
|
||
<span id="tut-string-pattern-matching"></span><h2><span class="section-number">10.5. </span>String Pattern Matching<a class="headerlink" href="#string-pattern-matching" title="Link to this heading">¶</a></h2>
|
||
<p>The <a class="reference internal" href="../library/re.html#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></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-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </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="sa">r</span><span class="s1">'\bf[a-z]*'</span><span class="p">,</span> <span class="s1">'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="sa">r</span><span class="s1">'(\b[a-z]+) \1'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'\1'</span><span class="p">,</span> <span class="s1">'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-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="s1">'tea for too'</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s1">'too'</span><span class="p">,</span> <span class="s1">'two'</span><span class="p">)</span>
|
||
<span class="go">'tea for two'</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="mathematics">
|
||
<span id="tut-mathematics"></span><h2><span class="section-number">10.6. </span>Mathematics<a class="headerlink" href="#mathematics" title="Link to this heading">¶</a></h2>
|
||
<p>The <a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">math</span></code></a> module gives access to the underlying C library functions for
|
||
floating-point math:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </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="mi">4</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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">random</span></code></a> module provides tools for making random selections:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </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="s1">'apple'</span><span class="p">,</span> <span class="s1">'pear'</span><span class="p">,</span> <span class="s1">'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">range</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="c1"># 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="c1"># random float from the interval [0.0, 1.0)</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="c1"># random integer chosen from range(6)</span>
|
||
<span class="go">4</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The <a class="reference internal" href="../library/statistics.html#module-statistics" title="statistics: Mathematical statistics functions"><code class="xref py py-mod docutils literal notranslate"><span class="pre">statistics</span></code></a> module calculates basic statistical properties
|
||
(the mean, median, variance, etc.) of numeric data:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">statistics</span>
|
||
<span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="p">[</span><span class="mf">2.75</span><span class="p">,</span> <span class="mf">1.75</span><span class="p">,</span> <span class="mf">1.25</span><span class="p">,</span> <span class="mf">0.25</span><span class="p">,</span> <span class="mf">0.5</span><span class="p">,</span> <span class="mf">1.25</span><span class="p">,</span> <span class="mf">3.5</span><span class="p">]</span>
|
||
<span class="gp">>>> </span><span class="n">statistics</span><span class="o">.</span><span class="n">mean</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
|
||
<span class="go">1.6071428571428572</span>
|
||
<span class="gp">>>> </span><span class="n">statistics</span><span class="o">.</span><span class="n">median</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
|
||
<span class="go">1.25</span>
|
||
<span class="gp">>>> </span><span class="n">statistics</span><span class="o">.</span><span class="n">variance</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
|
||
<span class="go">1.3720238095238095</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>The SciPy project <<a class="reference external" href="https://scipy.org">https://scipy.org</a>> has many other modules for numerical
|
||
computations.</p>
|
||
</section>
|
||
<section id="internet-access">
|
||
<span id="tut-internet-access"></span><h2><span class="section-number">10.7. </span>Internet Access<a class="headerlink" href="#internet-access" title="Link to this heading">¶</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/urllib.request.html#module-urllib.request" title="urllib.request: Extensible library for opening URLs."><code class="xref py py-mod docutils literal notranslate"><span class="pre">urllib.request</span></code></a> for retrieving data
|
||
from URLs and <a class="reference internal" href="../library/smtplib.html#module-smtplib" title="smtplib: SMTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">smtplib</span></code></a> for sending mail:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">urllib.request</span><span class="w"> </span><span class="kn">import</span> <span class="n">urlopen</span>
|
||
<span class="gp">>>> </span><span class="k">with</span> <span class="n">urlopen</span><span class="p">(</span><span class="s1">'http://worldtimeapi.org/api/timezone/etc/UTC.txt'</span><span class="p">)</span> <span class="k">as</span> <span class="n">response</span><span class="p">:</span>
|
||
<span class="gp">... </span> <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">response</span><span class="p">:</span>
|
||
<span class="gp">... </span> <span class="n">line</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span> <span class="c1"># Convert bytes to a str</span>
|
||
<span class="gp">... </span> <span class="k">if</span> <span class="n">line</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s1">'datetime'</span><span class="p">):</span>
|
||
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">line</span><span class="o">.</span><span class="n">rstrip</span><span class="p">())</span> <span class="c1"># Remove trailing newline</span>
|
||
<span class="gp">...</span>
|
||
<span class="go">datetime: 2022-01-01T01:36:47.689215+00:00</span>
|
||
|
||
<span class="gp">>>> </span><span class="kn">import</span><span class="w"> </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="s1">'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="s1">'soothsayer@example.org'</span><span class="p">,</span> <span class="s1">'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="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>
|
||
</section>
|
||
<section id="dates-and-times">
|
||
<span id="tut-dates-and-times"></span><h2><span class="section-number">10.8. </span>Dates and Times<a class="headerlink" href="#dates-and-times" title="Link to this heading">¶</a></h2>
|
||
<p>The <a class="reference internal" href="../library/datetime.html#module-datetime" title="datetime: Basic date and time types."><code class="xref py py-mod docutils literal notranslate"><span class="pre">datetime</span></code></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-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="c1"># dates are easily constructed and formatted</span>
|
||
<span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">datetime</span><span class="w"> </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="s2">"%m-</span><span class="si">%d</span><span class="s2">-%y. </span><span class="si">%d</span><span class="s2"> %b %Y is a %A on the </span><span class="si">%d</span><span class="s2"> 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="c1"># 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>
|
||
</section>
|
||
<section id="data-compression">
|
||
<span id="tut-data-compression"></span><h2><span class="section-number">10.9. </span>Data Compression<a class="headerlink" href="#data-compression" title="Link to this heading">¶</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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zlib</span></code></a>, <a class="reference internal" href="../library/gzip.html#module-gzip" title="gzip: Interfaces for gzip compression and decompression using file objects."><code class="xref py py-mod docutils literal notranslate"><span class="pre">gzip</span></code></a>, <a class="reference internal" href="../library/bz2.html#module-bz2" title="bz2: Interfaces for bzip2 compression and decompression."><code class="xref py py-mod docutils literal notranslate"><span class="pre">bz2</span></code></a>, <a class="reference internal" href="../library/lzma.html#module-lzma" title="lzma: A Python wrapper for the liblzma compression library."><code class="xref py py-mod docutils literal notranslate"><span class="pre">lzma</span></code></a>, <a class="reference internal" href="../library/zipfile.html#module-zipfile" title="zipfile: Read and write ZIP-format archive files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zipfile</span></code></a> and
|
||
<a class="reference internal" href="../library/tarfile.html#module-tarfile" title="tarfile: Read and write tar-format archive files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">tarfile</span></code></a>.</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">zlib</span>
|
||
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">'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">b'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>
|
||
</section>
|
||
<section id="performance-measurement">
|
||
<span id="tut-performance-measurement"></span><h2><span class="section-number">10.10. </span>Performance Measurement<a class="headerlink" href="#performance-measurement" title="Link to this heading">¶</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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code></a>
|
||
module quickly demonstrates a modest performance advantage:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">timeit</span><span class="w"> </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="s1">'t=a; a=b; b=t'</span><span class="p">,</span> <span class="s1">'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="s1">'a,b = b,a'</span><span class="p">,</span> <span class="s1">'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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code></a>’s fine level of granularity, the <a class="reference internal" href="../library/profile.html#module-profile" title="profile: Python source profiler."><code class="xref py py-mod docutils literal notranslate"><span class="pre">profile</span></code></a> and
|
||
<a class="reference internal" href="../library/profile.html#module-pstats" title="pstats: Statistics object for use with the profiler."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pstats</span></code></a> modules provide tools for identifying time critical sections in
|
||
larger blocks of code.</p>
|
||
</section>
|
||
<section id="quality-control">
|
||
<span id="tut-quality-control"></span><h2><span class="section-number">10.11. </span>Quality Control<a class="headerlink" href="#quality-control" title="Link to this heading">¶</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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">doctest</span></code></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-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">average</span><span class="p">(</span><span class="n">values</span><span class="p">):</span>
|
||
<span class="w"> </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="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="w"> </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="c1"># 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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">unittest</span></code></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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">doctest</span></code></a> module,
|
||
but it allows a more comprehensive set of tests to be maintained in a separate
|
||
file:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">unittest</span>
|
||
|
||
<span class="k">class</span><span class="w"> </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="w"> </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="c1"># Calling from the command line invokes all tests</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="batteries-included">
|
||
<span id="tut-batteries-included"></span><h2><span class="section-number">10.12. </span>Batteries Included<a class="headerlink" href="#batteries-included" title="Link to this heading">¶</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><p>The <a class="reference internal" href="../library/xmlrpc.client.html#module-xmlrpc.client" title="xmlrpc.client: XML-RPC client access."><code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpc.client</span></code></a> and <a class="reference internal" href="../library/xmlrpc.server.html#module-xmlrpc.server" title="xmlrpc.server: Basic XML-RPC server implementations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpc.server</span></code></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.</p></li>
|
||
<li><p>The <a class="reference internal" href="../library/email.html#module-email" title="email: Package supporting the parsing, manipulating, and generating email messages."><code class="xref py py-mod docutils literal notranslate"><span class="pre">email</span></code></a> package is a library for managing email messages, including
|
||
MIME and other <span class="target" id="index-1"></span><a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc2822.html"><strong>RFC 2822</strong></a>-based message documents. Unlike <a class="reference internal" href="../library/smtplib.html#module-smtplib" title="smtplib: SMTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">smtplib</span></code></a> and
|
||
<a class="reference internal" href="../library/poplib.html#module-poplib" title="poplib: POP3 protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">poplib</span></code></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.</p></li>
|
||
<li><p>The <a class="reference internal" href="../library/json.html#module-json" title="json: Encode and decode the JSON format."><code class="xref py py-mod docutils literal notranslate"><span class="pre">json</span></code></a> package provides robust support for parsing this
|
||
popular data interchange format. The <a class="reference internal" href="../library/csv.html#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module supports
|
||
direct reading and writing of files in Comma-Separated Value format,
|
||
commonly supported by databases and spreadsheets. XML processing is
|
||
supported by the <a class="reference internal" href="../library/xml.etree.elementtree.html#module-xml.etree.ElementTree" title="xml.etree.ElementTree: Implementation of the ElementTree API."><code class="xref py py-mod docutils literal notranslate"><span class="pre">xml.etree.ElementTree</span></code></a>, <a class="reference internal" href="../library/xml.dom.html#module-xml.dom" title="xml.dom: Document Object Model API for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">xml.dom</span></code></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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">xml.sax</span></code></a> packages. Together, these modules and packages
|
||
greatly simplify data interchange between Python applications and
|
||
other tools.</p></li>
|
||
<li><p>The <a class="reference internal" href="../library/sqlite3.html#module-sqlite3" title="sqlite3: A DB-API 2.0 implementation using SQLite 3.x."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sqlite3</span></code></a> module is a wrapper for the SQLite database
|
||
library, providing a persistent database that can be updated and
|
||
accessed using slightly nonstandard SQL syntax.</p></li>
|
||
<li><p>Internationalization is supported by a number of modules including
|
||
<a class="reference internal" href="../library/gettext.html#module-gettext" title="gettext: Multilingual internationalization services."><code class="xref py py-mod docutils literal notranslate"><span class="pre">gettext</span></code></a>, <a class="reference internal" href="../library/locale.html#module-locale" title="locale: Internationalization services."><code class="xref py py-mod docutils literal notranslate"><span class="pre">locale</span></code></a>, and the <a class="reference internal" href="../library/codecs.html#module-codecs" title="codecs: Encode and decode data and streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code></a> package.</p></li>
|
||
</ul>
|
||
</section>
|
||
</section>
|
||
|
||
|
||
<div class="clearer"></div>
|
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<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>
|
||
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|
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|
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