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<!DOCTYPE html>
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<title>Argumentos somente por palavra chave - import None</title>
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Argumentos somente por palavra chave
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<i class="fa fa-calendar"></i><time datetime="2015-03-28T19:00:00-03:00"> Sáb 28 março 2015</time>
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<h2>Por que falar sobre isto?</h2>
<p>Python 3 ainda possui uma névoa sobre ele, e o movimento de resistência ainda é grande. Mas isto não quer dizer que desbravadores já não o estejam explorando. Já escrevi um <a href="http://cassiobotaro.github.io/porque-python-3.html">post</a> sobre a nova versão da linguagem, porém ainda tem vários recursos que podem ser demonstrados. Um deles é a capacidade de aceitar somente palavras chaves como argumento. Eu até coloquei isto nos slides da Python Brasil 10, porém senti que ao apresentar faltou uma boa explicação.</p>
<h2>Talk is cheap. Show me the code</h2>
<p>Tentarei dar um exemplo utilizando código, explicarei utilizando os comentários</p>
<div class="highlight"><pre><span class="c"># vamos iniciar com a seguinte função</span>
<span class="k">def</span> <span class="nf">funcao</span><span class="p">(</span><span class="n">arg1</span><span class="p">,</span> <span class="n">arg2</span><span class="p">,</span> <span class="n">kill</span><span class="o">=</span><span class="bp">False</span><span class="p">):</span>
<span class="k">if</span> <span class="n">kill</span><span class="p">:</span>
<span class="n">shutil</span><span class="o">.</span><span class="n">rmtree</span><span class="p">(</span><span class="s">'/'</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="c"># realiza operacao</span>
<span class="o">...</span>
<span class="c"># e por algum algum descuido...</span>
<span class="n">funcao</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="mi">3</span><span class="p">)</span>
<span class="c"># o que acontece?</span>
<span class="c"># possivelmente você acaba de ser demitido</span>
<span class="c"># Agora vamos corrigir isto utilizando python3</span>
<span class="c"># lembre-se que daqui pra baixo, a sintáxe não é compativel com python 2</span>
<span class="k">def</span> <span class="nf">funcao</span><span class="p">(</span><span class="n">arg1</span><span class="p">,</span> <span class="n">arg2</span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">kill</span><span class="o">=</span><span class="bp">False</span><span class="p">):</span>
<span class="k">if</span> <span class="n">kill</span><span class="p">:</span>
<span class="n">shutil</span><span class="o">.</span><span class="n">rmtree</span><span class="p">(</span><span class="s">'/'</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="c"># realiza operacao</span>
<span class="o">...</span>
<span class="c"># Basta colocar um * e pronto</span>
<span class="c"># agora se cometer um erro o python 3 te alerta</span>
<span class="n">funcao</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="mi">3</span><span class="p">)</span>
<span class="c"># TypeError: funcao() takes 2 positional arguments but 3 were given</span>
<span class="c"># Mas o que é esse asterico, é igual o args?</span>
<span class="c"># Na verdade é similar, porém o interpretador sabe que se não foi definido o </span>
<span class="c"># "args" um erro deve ser lançado</span>
<span class="c">#Mas e se eu definir o args?</span>
<span class="k">def</span> <span class="nf">funcao</span><span class="p">(</span><span class="n">arg1</span><span class="p">,</span> <span class="n">arg2</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="n">kill</span><span class="o">=</span><span class="bp">False</span><span class="p">):</span>
<span class="k">if</span> <span class="n">kill</span><span class="p">:</span>
<span class="n">shutil</span><span class="o">.</span><span class="n">rmtree</span><span class="p">(</span><span class="s">'/'</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="c"># realiza operacao</span>
<span class="o">...</span>
<span class="c"># acontece que agora, todo parâmetro passado além dos dois obrigatórios(positionals), será armazenado em args, e kill só sera atribuido quando</span>
<span class="c"># utilizado palavra chave</span>
<span class="c">#Ex: funcao(0, 0, kill=True)</span>
</pre></div>
<h2>Considerações finais</h2>
<p>Não pense que exemplo é exagerado, pode acontecer a qualquer hora com você.
Não brinque mais de roleta russa com seus argumentos.</p>
<p><img alt="programming-motherfucker" src="../images/programming-motherfucker.jpg" /></p>
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