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<h1 id="topic_header_text">Immuable vs mutable</h1>
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<ul style="text-indent: 0px; padding: 0; margin: 0 0 0 24px; list-style-position: outside; list-style-type: disc;">
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<li class="rvps2"><span class="rvts64">Immuable ou immuable</span></li>
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<p class="rvps2"><span class="rvts25">Les </span><span class="rvts35">nombres </span><span class="rvts25">sont des </span><span class="rvts35">types immuables</span><span class="rvts25"> tout comme les </span><span class="rvts35">chaînes de caractères</span><span class="rvts25"> et les </span><span class="rvts35">tuples</span><span class="rvts25"> (tableaux d’objets). </span></p>
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<p class="rvps2"><span class="rvts25">Une variable de type immuable ne peut être modifiée. Une opération sur une variable de ce type entraîne nécessairement la création d’une autre variable du même type.</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps2"><span class="rvts25">Pour mettre en évidence cette propriété, jouons avec la fonction </span><span class="rvts35">id()</span><span class="rvts25"> qui renvoie l'identificateur unique d'un objet, cela correspond à l'adresse mémoire dans laquelle il est stocké. </span></p>
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<p class="rvps2"><span class="rvts25">Si l'identifiant est le même, c'est le même objet.</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps2"><span class="rvts11">Vous allez vérifier cela dans la Console Python (interpréteur Python en mode interactif) </span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> a = 1</span><br/><span class="rvts63">>>> id(a)</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> a += 2</span><br/><span class="rvts63">>>> print(a)</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> id(a)</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> b = a</span><br/><span class="rvts63">>>> id(b)</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps2"><span class="rvts25">Donner plusieurs noms à un même objet s'appelle l'</span><span class="rvts35">aliasing, </span><span class="rvts25">les variables </span><span class="rvts35">a</span><span class="rvts25"> et </span><span class="rvts35">b</span><span class="rvts25"> sont des</span><span class="rvts35"> alias </span><span class="rvts25">l'une de l'autre. </span><span class="rvts35">a</span><span class="rvts25"> et </span><span class="rvts35">b</span><span class="rvts25"> pointent vers le même emplacement mémoire</span></p>
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<p class="rvps2"><span class="rvts35"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> b = 5</span><br/><span class="rvts63">>>> a</span></p>
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<p class="rvps2"><span class="rvts35"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> b</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> id(a)</span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> id(a)</span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<p class="rvps2"><span class="rvts25">Conclusion, l'aliasing se fait sans risque.</span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<ul style="text-indent: 0px; padding: 0; margin: 0 0 0 24px; list-style-position: outside; list-style-type: disc;">
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<li class="rvps2"><span class="rvts64">Mutable</span></li>
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</ul>
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<p class="rvps2"><span class="rvts25">Un objet de type </span><span class="rvts35">mutable</span><span class="rvts25"> peut être modifié et modifié in situ. Aucune copie implicite n'est faite.</span></p>
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<p class="rvps2"><span class="rvts25">Cette catégorie comprend: les </span><span class="rvts35">listes</span><span class="rvts25">, les </span><span class="rvts35">dictionnaires</span><span class="rvts25">, ...</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> liste1 = []</span><br/><span class="rvts63">>>> id(liste1)</span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> liste1.append('Nicolas')</span><br/><span class="rvts63">>>> liste1</span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> id(liste1)</span></p>
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<p class="rvps2"><span class="rvts64"><br/></span></p>
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<p class="rvps2"><span class="rvts25">La valeur de liste peut être modifié mais liste ne change pas d'id.</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps2"><span class="rvts25">Si un objet doit être souvent modifié, un type mutable est préférable qu'un type immuable d'un point de vue espace mémoire mais attention à l'aliasing par exemple:</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> liste2 = liste1</span><br/><span class="rvts63">>>> id(liste2)</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps10"><span class="rvts63">>>> liste2.append(3)</span><br/><span class="rvts63">>>> liste2</span></p>
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<p class="rvps10"><span class="rvts63">>>> liste1</span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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<p class="rvps2"><span class="rvts25"><br/></span></p>
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