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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
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<title>Loops — Introduction to Programming with Python</title>
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<div class="body">
<div class="section" id="loops">
<h1>Loops<a class="headerlink" href="#loops" title="Permalink to this headline">¶</a></h1>
<div class="section" id="introduction">
<h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
<p>One more thing: Our programs often featured repetition. There is a powerful
concept in Python called looping, which we will elaborate later on. For now,
take this easy example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="k">print</span><span class="p">(</span><span class="s">"Hello!"</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="drawing-a-dashed-line">
<h2>Drawing a dashed line<a class="headerlink" href="#drawing-a-dashed-line" title="Permalink to this headline">¶</a></h2>
<div class="section" id="exercise">
<h3>Exercise<a class="headerlink" href="#exercise" title="Permalink to this headline">¶</a></h3>
<p>Draw a dashed line. You can move the turtle without tracing a line behind you
with the <tt class="docutils literal"><span class="pre">turtle.penup()</span></tt> function; put it back on the ground with
<tt class="docutils literal"><span class="pre">turtle.pendown()</span></tt>.</p>
<img alt="_images/dashed.png" src="_images/dashed.png" />
</div>
<div class="section" id="solution">
<h3>Solution<a class="headerlink" href="#solution" title="Permalink to this headline">¶</a></h3>
<div class="highlight-python"><div class="highlight"><pre><span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="mi">15</span><span class="p">)</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">penup</span><span class="p">()</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">pendown</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="bonus">
<h3>Bonus<a class="headerlink" href="#bonus" title="Permalink to this headline">¶</a></h3>
<p>Can you make the dashes become larger as the line progresses?</p>
<img alt="_images/dashedprogressing.png" src="_images/dashedprogressing.png" />
</div>
</div>
<div class="section" id="honeycomb-loops">
<h2>Honeycomb loops<a class="headerlink" href="#honeycomb-loops" title="Permalink to this headline">¶</a></h2>
<div class="section" id="id1">
<h3>Exercise<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h3>
<p>Take your honeycomb program and make it easier with loops. How small can you
get it?</p>
</div>
<div class="section" id="id2">
<h3>Solution<a class="headerlink" href="#id2" title="Permalink to this headline">¶</a></h3>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">hexagon</span><span class="p">():</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">6</span><span class="p">):</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">left</span><span class="p">(</span><span class="mi">60</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">6</span><span class="p">):</span>
<span class="n">hexagon</span><span class="p">()</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">right</span><span class="p">(</span><span class="mi">60</span><span class="p">)</span>
</pre></div>
</div>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Loops</a><ul>
<li><a class="reference internal" href="#introduction">Introduction</a></li>
<li><a class="reference internal" href="#drawing-a-dashed-line">Drawing a dashed line</a><ul>
<li><a class="reference internal" href="#exercise">Exercise</a></li>
<li><a class="reference internal" href="#solution">Solution</a></li>
<li><a class="reference internal" href="#bonus">Bonus</a></li>
</ul>
</li>
<li><a class="reference internal" href="#honeycomb-loops">Honeycomb loops</a><ul>
<li><a class="reference internal" href="#id1">Exercise</a></li>
<li><a class="reference internal" href="#id2">Solution</a></li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="functions.html"
title="previous chapter">User-defined functions</a></p>
<h4>Next topic</h4>
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title="next chapter">Functions with parameters</a></p>
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