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<div class="section" id="variables">
<h1>Variables<a class="headerlink" href="#variables" title="제목 주소">¶</a></h1>
<div class="section" id="introduction">
<h2>Introduction<a class="headerlink" href="#introduction" title="제목 주소">¶</a></h2>
<p>Whew. Experimenting with the angles requires you to change three different
places in the code each time. Imagine you’d want to experiment with
all of the square sizes, let alone with rectangles! We can do better than that.</p>
<p>This is where <strong>variables</strong> come into play: You can tell Python that from now on,
whenever you refer to a variable, you actually mean something else. That concept
might be familiar from symbolic maths, where you would write: <em>Let x be 5.</em>
Then <em>x * 2</em> will obviously be <em>10</em>.</p>
<p>In Python syntax, that very statement translates to:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">x</span> <span class="o">=</span> <span class="mi">5</span>
</pre></div>
</div>
<p>After that statement, if you do <code class="docutils literal"><span class="pre">print(x)</span></code>, it will actually output its value
— 5. Well, can use that for your turtle too:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">turtle</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
</pre></div>
</div>
<p>Variables can store all sorts of things, not just numbers. A typical
other thing you want to have stored often is a <strong>string</strong> - a line of text.
Strings are indicated with a starting and a leading <code class="docutils literal"><span class="pre">"</span></code> (double quote).
You’ll learn about this and other types, as those are called in Python, and
what you can do with them later on.</p>
<p>You can even use a variable to give the turtle a name:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">timmy</span> <span class="o">=</span> <span class="n">turtle</span>
</pre></div>
</div>
<p>Now every time you type <code class="docutils literal"><span class="pre">timmy</span></code> it knows you mean <code class="docutils literal"><span class="pre">turtle</span></code>. You can
still continue to use <code class="docutils literal"><span class="pre">turtle</span></code> as well:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">timmy</span><span class="o">.</span><span class="n">forward</span><span class="p">(</span><span class="mi">50</span><span class="p">)</span>
<span class="n">timmy</span><span class="o">.</span><span class="n">left</span><span class="p">(</span><span class="mi">90</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">50</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="a-variable-called-angle">
<h2>A variable called angle<a class="headerlink" href="#a-variable-called-angle" title="제목 주소">¶</a></h2>
<div class="section" id="exercise">
<h3>Exercise<a class="headerlink" href="#exercise" title="제목 주소">¶</a></h3>
<p>If we have a variable called <code class="docutils literal"><span class="pre">angle</span></code>, how could we use that to experiment
much faster with our tilted squares program?</p>
</div>
<div class="solution section" id="solution">
<h3>Solution<a class="headerlink" href="#solution" title="제목 주소">¶</a></h3>
<div class="highlight-python"><div class="highlight"><pre><span class="n">angle</span> <span class="o">=</span> <span class="mi">20</span>
<span class="n">turtle</span><span class="o">.</span><span class="n">left</span><span class="p">(</span><span class="n">angle</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">50</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">90</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">50</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">90</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">50</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">90</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">50</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">90</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="n">angle</span><span class="p">)</span>
</pre></div>
</div>
<p>... and so on</p>
</div>
<div class="section" id="bonus">
<h3>Bonus<a class="headerlink" href="#bonus" title="제목 주소">¶</a></h3>
<p>Can you apply that principle to the size of the squares, too?</p>
</div>
</div>
<div class="section" id="the-house-of-santa-claus">
<h2>The house of santa claus<a class="headerlink" href="#the-house-of-santa-claus" title="제목 주소">¶</a></h2>
<div class="section" id="id1">
<h3>Exercise<a class="headerlink" href="#id1" title="제목 주소">¶</a></h3>
<p>Draw a house.</p>
<img alt="_images/house.png" src="_images/house.png" />
<p>You can calculate the length of the diagonal line with the Pythagorean
theorem. That value is a good candidate to store in a variable. To calculate
the square root of a number in Python, you’ll need to import the <em>math</em> module
and use the <code class="docutils literal"><span class="pre">math.sqrt()</span></code> function. The square of a number is calculated
with the <code class="docutils literal"><span class="pre">**</span></code> operator:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">math</span>
<span class="n">c</span> <span class="o">=</span> <span class="n">math</span><span class="o">.</span><span class="n">sqrt</span><span class="p">(</span><span class="n">a</span><span class="o">**</span><span class="mi">2</span> <span class="o">+</span> <span class="n">b</span><span class="o">**</span><span class="mi">2</span><span class="p">)</span>
</pre></div>
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