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<div class="section" id="lambdas">
<h1>Lambdas</h1>
<p>Lambdas are one line functions. They are also known as anonymous
functions in some other languages. You might want to use lambdas when
you don’t want to use a function twice in a program. They are just like
normal functions and even behave like them.</p>
<p><strong>Blueprint</strong></p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="k">lambda</span> <span class="n">argument</span><span class="p">:</span> <span class="n">manipulate</span><span class="p">(</span><span class="n">argument</span><span class="p">)</span>
</pre></div>
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<p><strong>Example</strong></p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="n">add</span> <span class="o">=</span> <span class="k">lambda</span> <span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">:</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span>
<span class="k">print</span><span class="p">(</span><span class="n">add</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p">))</span>
<span class="c"># Output: 8</span>
</pre></div>
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<p>Here are a few useful use cases for lambdas and just a few way in which
they are used in the wild:</p>
<p><strong>List sorting</strong></p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="n">a</span> <span class="o">=</span> <span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">),</span> <span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span> <span class="p">(</span><span class="mi">9</span><span class="p">,</span> <span class="mi">10</span><span class="p">),</span> <span class="p">(</span><span class="mi">13</span><span class="p">,</span> <span class="o">-</span><span class="mi">3</span><span class="p">)]</span>
<span class="n">a</span><span class="o">.</span><span class="n">sort</span><span class="p">(</span><span class="n">key</span><span class="o">=</span><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="n">x</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span>
<span class="k">print</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>
<span class="c"># Output: [(13, -3), (4, 1), (1, 2), (9, 10)]</span>
</pre></div>
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<p><strong>Parallel sorting of lists</strong></p>
<div class="code python highlight-python"><div class="highlight"><pre><span class="n">data</span> <span class="o">=</span> <span class="nb">zip</span><span class="p">(</span><span class="n">list1</span><span class="p">,</span> <span class="n">list2</span><span class="p">)</span>
<span class="n">data</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span>
<span class="n">list1</span><span class="p">,</span> <span class="n">list2</span> <span class="o">=</span> <span class="nb">map</span><span class="p">(</span><span class="k">lambda</span> <span class="n">t</span><span class="p">:</span> <span class="nb">list</span><span class="p">(</span><span class="n">t</span><span class="p">),</span> <span class="nb">zip</span><span class="p">(</span><span class="o">*</span><span class="n">data</span><span class="p">))</span>
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<p>Note: We will learn about map in a later chapter so don’t worry!</p>
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