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<title>Les design patterns &#8212; Documentation Formation Python 1</title>
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<h1>&nbsp; &nbsp; Programmation python</h1>
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<p>&nbsp;</p>
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<div class="section" id="les-design-patterns">
<h1>Les design patterns<a class="headerlink" href="#les-design-patterns" title="Lien permanent vers ce titre"></a></h1>
<p>Les design patterns <strong>ne sont pas</strong> indépendants du langage.
Ils dépendent de l’implémentation.</p>
<div class="section" id="le-duck-typing">
<h2>Le duck typing<a class="headerlink" href="#le-duck-typing" title="Lien permanent vers ce titre"></a></h2>
<p>En python, le duck typing est une forme extreme de programmation par interface.
Ne pas hériter dans des directions fausse</p>
<p>exemple : une voiture ne peut hériter d’un moteur, parce que un moteur n’est pas une voiture.</p>
</div>
<div class="section" id="hold-or-wrap">
<h2>hold or wrap ?<a class="headerlink" href="#hold-or-wrap" title="Lien permanent vers ce titre"></a></h2>
<p><strong>hold</strong>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">O</span><span class="o">.</span><span class="n">S</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
</pre></div>
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<p>Cela induit un couplage fort (cf la loi de Demeter)</p>
<div class="admonition important">
<p class="first admonition-title">Important</p>
<p class="last">law of Demeter : never more than one dot.</p>
</div>
<p>wrap : a hold by private name, with a:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="bp">self</span><span class="o">.</span><span class="n">S</span><span class="o">.</span><span class="n">method</span><span class="p">()</span>
</pre></div>
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<p>Ou bien une méthode getattr:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="fm">__getattr__</span><span class="p">()</span>
</pre></div>
</div>
<p>Gets coupling right.</p>
</div>
<div class="section" id="wrapper-can-restrict-inheritance-cannot-restrict">
<h2>wrapper can restrict, inheritance cannot restrict<a class="headerlink" href="#wrapper-can-restrict-inheritance-cannot-restrict" title="Lien permanent vers ce titre"></a></h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">RestrictingWrapper</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">w</span><span class="p">,</span> <span class="n">block</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_w</span> <span class="o">=</span> <span class="n">w</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_block</span> <span class="o">=</span> <span class="n">block</span>
<span class="k">def</span> <span class="nf">__getattr__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">n</span><span class="p">):</span>
<span class="k">if</span> <span class="n">n</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">_block</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">AttributeError</span><span class="p">,</span> <span class="n">n</span>
<span class="k">return</span> <span class="nb">getattr</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_w</span><span class="p">,</span> <span class="n">n</span><span class="p">)</span>
</pre></div>
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</div>
<div class="section" id="pattern-de-creation-singleton">
<h2>Pattern de création : singleton<a class="headerlink" href="#pattern-de-creation-singleton" title="Lien permanent vers ce titre"></a></h2>
<p># utiliser un module au lieu d’une classe</p>
<p>in <cite>toto.py</cite>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Toto</span><span class="p">()</span>
<span class="n">toto</span> <span class="o">=</span> <span class="n">Toto</span><span class="p">()</span>
</pre></div>
</div>
<p>in another module:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">toto</span> <span class="k">import</span> <span class="n">toto</span>
</pre></div>
</div>
</div>
<div class="section" id="la-factory">
<h2>la factory<a class="headerlink" href="#la-factory" title="Lien permanent vers ce titre"></a></h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">load</span><span class="p">(</span><span class="n">pkg</span><span class="p">,</span> <span class="n">obj</span><span class="p">):</span>
<span class="n">m</span> <span class="o">=</span> <span class="nb">__import__</span><span class="p">(</span><span class="n">pkg</span><span class="p">,</span> <span class="p">{},</span> <span class="p">{},</span> <span class="p">[</span><span class="n">obj</span><span class="p">])</span>
<span class="k">return</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">m</span><span class="p">,</span> <span class="n">obj</span><span class="p">)</span>
<span class="bp">cls</span> <span class="o">=</span> <span class="n">load</span><span class="p">(</span><span class="s1">&#39;p1.p2.p3&#39;</span><span class="p">,</span> <span class="s1">&#39;c4&#39;</span><span class="p">)</span>
</pre></div>
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</div>
<div class="section" id="template-method-self-delegation">
<h2>template method (self delegation)<a class="headerlink" href="#template-method-self-delegation" title="Lien permanent vers ce titre"></a></h2>
<p># Abstract base class:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">OrganiseMethod</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">org_method</span><span class="p">():</span>
<span class="k">def</span> <span class="nf">do_this</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">do_that</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">Concrete</span><span class="p">(</span><span class="n">OrganiseMethod</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">do_this</span><span class="p">():</span> <span class="o">...</span>
<span class="k">def</span> <span class="nf">do_that</span><span class="p">():</span> <span class="o">...</span>
</pre></div>
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<p>il est préférable de lever une NotImplementedError, ce qui revient à faire
une classe abstraite.</p>
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