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<div class="document" id="object-oriented-programming">
<h1 class="title">Object-oriented programming</h1>
<p>(<strong>Programação orientada a objetos</strong>)</p>
<p>Daniel Moser</p>
<p>Feb 14th, 2017</p>
<p>2nd IAG Python Boot Camp</p>
<div class="contents topic" id="table-of-contents">
<p class="topic-title first">Table of contents</p>
<ul class="simple">
<li><a class="reference internal" href="#what-is-oop" id="id1">What is OOP?</a></li>
<li><a class="reference internal" href="#oop-concepts-abstraction-class-and-object" id="id2">OOP Concepts: abstraction, class and object</a></li>
<li><a class="reference internal" href="#examples" id="id3">Examples</a></li>
<li><a class="reference internal" href="#oop-concepts-heritage" id="id4">OOP Concepts: heritage</a></li>
<li><a class="reference internal" href="#ways-of-combining-classes-and-their-properties" id="id5">Ways of combining classes and their properties</a></li>
<li><a class="reference internal" href="#encapsulation-and-polymorphism" id="id6">Encapsulation and polymorphism</a></li>
<li><a class="reference internal" href="#other-oop-concepts" id="id7">Other OOP Concepts</a></li>
<li><a class="reference internal" href="#oop-pro-et-contra" id="id8">OOP pro et contra</a></li>
<li><a class="reference internal" href="#extra" id="id9">Extra</a></li>
<li><a class="reference internal" href="#exercises" id="id10">Exercises</a></li>
</ul>
</div>
<div class="section" id="what-is-oop">
<h1><a class="toc-backref" href="#id1">What is OOP?</a></h1>
<p><strong>OOP</strong> is a programming paradigm. It is usually compared with the traditional <strong>procedural</strong> programming.</p>
<p>The procedural programming is based on <em>procedures</em> (i.e., routines and sub-routines), where the procedures and data variables are <strong>independent</strong>. Examples: Cobol, C, Fortran...</p>
<pre class="code literal-block">
program Fibonacci;
function fib(n: Integer): Integer;
var a: Integer = 1;
b: Integer = 1;
f: Integer;
i: Integer;
begin
if (n = 1) or (n = 2) then
fib := 1
else
begin
for i := 3 to n do
begin
f := a + b;
b := a;
a := f;
end;
fib := f;
end;
end;
begin
WriteLn(fib(6));
end.
</pre>
<p>OOP is based in <strong>objects</strong>, a variable that combines <em>methods</em> (procedures) and <em>attributes</em> (data).</p>
<p>Examples of <em>OOP compatible</em> languages: C#, C++, Java, Lisp, Python, Ruby...</p>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">Fibonacci</span><span class="punctuation">:</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">cache</span> <span class="operator">=</span> <span class="punctuation">{}</span>
<span class="keyword">def</span> <span class="name function">fib</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">n</span><span class="punctuation">):</span>
<span class="keyword">if</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">cache</span><span class="operator">.</span><span class="name">has_key</span><span class="punctuation">(</span><span class="name">n</span><span class="punctuation">):</span>
<span class="keyword">return</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">cache</span><span class="punctuation">[</span><span class="name">n</span><span class="punctuation">]</span>
<span class="keyword">if</span> <span class="name">n</span> <span class="operator">==</span> <span class="literal number integer">1</span> <span class="operator word">or</span> <span class="name">n</span> <span class="operator">==</span> <span class="literal number integer">2</span><span class="punctuation">:</span>
<span class="keyword">return</span> <span class="literal number integer">1</span>
<span class="keyword">else</span><span class="punctuation">:</span>
<span class="name">a</span> <span class="operator">=</span> <span class="literal number integer">1</span>
<span class="name">b</span> <span class="operator">=</span> <span class="literal number integer">1</span>
<span class="keyword">for</span> <span class="name">i</span> <span class="operator word">in</span> <span class="name builtin">range</span><span class="punctuation">(</span><span class="literal number integer">2</span><span class="punctuation">,</span> <span class="name">n</span><span class="punctuation">):</span>
<span class="name">f</span> <span class="operator">=</span> <span class="name">a</span> <span class="operator">+</span> <span class="name">b</span><span class="punctuation">;</span>
<span class="name">b</span> <span class="operator">=</span> <span class="name">a</span><span class="punctuation">;</span>
<span class="name">a</span> <span class="operator">=</span> <span class="name">f</span><span class="punctuation">;</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">cache</span><span class="punctuation">[</span><span class="name">n</span><span class="punctuation">]</span> <span class="operator">=</span> <span class="name">f</span><span class="punctuation">;</span>
<span class="keyword">return</span> <span class="name">f</span><span class="punctuation">;</span>
<span class="name">fibonaccyCounter</span> <span class="operator">=</span> <span class="name">Fibonacci</span><span class="punctuation">()</span>
<span class="comment"># print(fibonaccyCounter.fib(600))</span>
<span class="comment"># %time fibonaccyCounter.fib(600)</span>
<span class="comment"># %time fibonaccyCounter.fib(600)</span>
</pre>
<p>Why <em>OOP compatible</em>? Because usually in a OOP language one can still work as a <strong>procedural</strong> language...</p>
<p>Examples of pure OOP languages: Smalltalk and Self.</p>
</div>
<div class="section" id="oop-concepts-abstraction-class-and-object">
<h1><a class="toc-backref" href="#id2">OOP Concepts: abstraction, class and object</a></h1>
<ul class="simple">
<li><strong>abstraction</strong> is the process of defining only the essential aspects in a specific context, ignoring non-relevant characteristics.</li>
<li><strong>class</strong> is an <em>abstraction</em> that defines a <strong>type</strong> of object and what objects of that type have within them (their <strong>attributes</strong>) and also defines what kind of actions that type of object is able to perform (<strong>methods</strong>).</li>
</ul>
<pre class="literal-block">
"Class has no life, it's just a concept."
</pre>
<ul class="simple">
<li><strong>object</strong> (or class <strong>instance</strong>) is a living variable, created according to a (conceptual) class.</li>
<li><strong>constructor</strong> has a special function: it serves to initialize attributes and runs automatically whenever you create a new object.</li>
</ul>
</div>
<div class="section" id="examples">
<h1><a class="toc-backref" href="#id3">Examples</a></h1>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">testing</span><span class="punctuation">:</span>
<span class="literal string doc">"""This is a IAG Python Boot Camp class definition"""</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">init_value</span><span class="punctuation">):</span>
<span class="literal string doc">"""This is a constructor"""</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">some_value</span> <span class="operator">=</span> <span class="name">init_value</span>
<span class="keyword">return</span>
<span class="keyword">def</span> <span class="name function">double_attr</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="literal string doc">"""This is a method that double the ``some_value`` atribute"""</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">some_value</span> <span class="operator">*=</span> <span class="literal number integer">2</span>
<span class="keyword">return</span>
</pre>
</div>
<div class="section" id="oop-concepts-heritage">
<h1><a class="toc-backref" href="#id4">OOP Concepts: heritage</a></h1>
<ul class="simple">
<li><strong>heritage</strong> is the mechanism by which one <em>class</em> can be extended to another one. The inheritance mechanism allows a class (subclass) to share the source code of another class (superclass), taking advantage of its behaviors (methods) and possible variables (attributes).</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">Pets</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="name">owner</span> <span class="operator">=</span> <span class="literal string">"Python Boot Camp"</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">name</span><span class="punctuation">,</span> <span class="name">age</span><span class="punctuation">,</span> <span class="name">condition</span><span class="operator">=</span><span class="literal string">'healthy'</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">"A new pet entry!"</span><span class="punctuation">)</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">name</span> <span class="operator">=</span> <span class="name">name</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">age</span> <span class="operator">=</span> <span class="name">age</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">condition</span> <span class="operator">=</span> <span class="name">condition</span>
<span class="keyword">def</span> <span class="name function">__repr__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">return</span> <span class="literal string">"Pet '{0}', {1} year(s)"</span><span class="operator">.</span><span class="name">format</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">name</span><span class="punctuation">,</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">age</span><span class="punctuation">)</span>
<span class="keyword">class</span> <span class="name class">Dog</span><span class="punctuation">(</span><span class="name">Pets</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">bark</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">" Woof-woof!!"</span><span class="punctuation">)</span>
<span class="keyword">return</span>
<span class="keyword">class</span> <span class="name class">Monkey</span><span class="punctuation">(</span><span class="name">Pets</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">name</span><span class="punctuation">,</span> <span class="name">age</span><span class="punctuation">,</span> <span class="name">condition</span><span class="operator">=</span><span class="literal string">''</span><span class="punctuation">):</span>
<span class="literal string doc">"""Overwriting the Pets() constructor"""</span>
<span class="name">condition</span> <span class="operator">=</span> <span class="literal string">'custom'</span>
<span class="name">Pets</span><span class="operator">.</span><span class="name">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">name</span><span class="punctuation">,</span> <span class="name">age</span><span class="punctuation">,</span> <span class="name">condition</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">gibber</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">" (gibber)!!"</span><span class="punctuation">)</span>
<span class="keyword">return</span>
<span class="keyword">class</span> <span class="name class">Horse</span><span class="punctuation">(</span><span class="name">Pets</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">name</span><span class="punctuation">,</span> <span class="name">age</span><span class="punctuation">):</span>
<span class="name builtin">super</span><span class="punctuation">(</span><span class="name">Horse</span><span class="punctuation">,</span> <span class="name builtin pseudo">self</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">__init__</span><span class="punctuation">(</span><span class="name">name</span><span class="punctuation">,</span> <span class="name">age</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">neigh</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">" Neigh!!"</span><span class="punctuation">)</span>
<span class="keyword">return</span>
<span class="keyword">class</span> <span class="name class">Cat</span><span class="punctuation">(</span><span class="name">Pets</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name builtin">super</span><span class="punctuation">(</span><span class="name">Pets</span><span class="punctuation">,</span> <span class="name builtin pseudo">self</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">__init__</span><span class="punctuation">()</span>
<span class="keyword">def</span> <span class="name function">meow</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">" Meow!!"</span><span class="punctuation">)</span>
<span class="keyword">return</span>
</pre>
<ul class="simple">
<li><strong>specialization</strong> is the inheritance process in which a subclass is created from existing superclass(es).</li>
<li><strong>generalization</strong> is the process in which a superclass is created from existing subclasses.</li>
<li>Python supports <strong>multiple inheritance</strong>:</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">Toys</span><span class="punctuation">:</span>
<span class="name">color</span> <span class="operator">=</span> <span class="literal string">'light blue'</span>
<span class="keyword">class</span> <span class="name class">Lassie</span><span class="punctuation">(</span><span class="name">Pets</span><span class="punctuation">,</span> <span class="name">Toys</span><span class="punctuation">):</span>
<span class="keyword">pass</span>
</pre>
<p>Must read: <a class="reference external" href="https://rhettinger.wordpress.com/2011/05/26/super-considered-super/">Python’s super() considered super!</a></p>
</div>
<div class="section" id="ways-of-combining-classes-and-their-properties">
<h1><a class="toc-backref" href="#id5">Ways of combining classes and their properties</a></h1>
<ul class="simple">
<li><strong>association</strong> is the mechanism by which one object uses the resources (<em>attributes</em>) of another.</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">A</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">a</span><span class="punctuation">,</span> <span class="name">b</span><span class="punctuation">,</span> <span class="name">c</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">a</span> <span class="operator">=</span> <span class="name">a</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">b</span> <span class="operator">=</span> <span class="name">b</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">c</span> <span class="operator">=</span> <span class="name">c</span>
<span class="keyword">def</span> <span class="name function">addNums</span><span class="punctuation">():</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">b</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">c</span>
<span class="keyword">class</span> <span class="name class">B</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">d</span><span class="punctuation">,</span> <span class="name">e</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">d</span> <span class="operator">=</span> <span class="name">d</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">e</span> <span class="operator">=</span> <span class="name">e</span>
<span class="keyword">def</span> <span class="name function">addAllNums</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">Ab</span><span class="punctuation">,</span> <span class="name">Ac</span><span class="punctuation">):</span>
<span class="name">x</span> <span class="operator">=</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">d</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">e</span> <span class="operator">+</span> <span class="name">Ab</span> <span class="operator">+</span> <span class="name">Ac</span>
<span class="keyword">return</span> <span class="name">x</span>
<span class="name">ting</span> <span class="operator">=</span> <span class="name">A</span><span class="punctuation">(</span><span class="literal string">"yo"</span><span class="punctuation">,</span> <span class="literal number integer">2</span><span class="punctuation">,</span> <span class="literal number integer">6</span><span class="punctuation">)</span>
<span class="name">ling</span> <span class="operator">=</span> <span class="name">B</span><span class="punctuation">(</span><span class="literal number integer">5</span><span class="punctuation">,</span> <span class="literal number integer">9</span><span class="punctuation">)</span>
<span class="keyword">print</span> <span class="name">ling</span><span class="operator">.</span><span class="name">addAllNums</span><span class="punctuation">(</span><span class="name">ting</span><span class="operator">.</span><span class="name">b</span><span class="punctuation">,</span> <span class="name">ting</span><span class="operator">.</span><span class="name">c</span><span class="punctuation">)</span>
</pre>
<ul class="simple">
<li><strong>coupling</strong> or <strong>aggregation</strong>: is the process where a (sub)class is (integrally) incorporated as an attribute of another one.</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">A</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">a</span><span class="punctuation">,</span> <span class="name">b</span><span class="punctuation">,</span> <span class="name">c</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">a</span> <span class="operator">=</span> <span class="name">a</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">b</span> <span class="operator">=</span> <span class="name">b</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">c</span> <span class="operator">=</span> <span class="name">c</span>
<span class="keyword">def</span> <span class="name function">addNums</span><span class="punctuation">():</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">b</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">c</span>
<span class="keyword">class</span> <span class="name class">B</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">d</span><span class="punctuation">,</span> <span class="name">e</span><span class="punctuation">,</span> <span class="name">A</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">d</span> <span class="operator">=</span> <span class="name">d</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">e</span> <span class="operator">=</span> <span class="name">e</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">A</span> <span class="operator">=</span> <span class="name">A</span>
<span class="keyword">def</span> <span class="name function">addAllNums</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name">x</span> <span class="operator">=</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">d</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">e</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">A</span><span class="operator">.</span><span class="name">b</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">A</span><span class="operator">.</span><span class="name">c</span>
<span class="keyword">return</span> <span class="name">x</span>
<span class="name">ting</span> <span class="operator">=</span> <span class="name">A</span><span class="punctuation">(</span><span class="literal string">"yo"</span><span class="punctuation">,</span> <span class="literal number integer">2</span><span class="punctuation">,</span> <span class="literal number integer">6</span><span class="punctuation">)</span>
<span class="name">ling</span> <span class="operator">=</span> <span class="name">B</span><span class="punctuation">(</span><span class="literal number integer">5</span><span class="punctuation">,</span> <span class="literal number integer">9</span><span class="punctuation">,</span> <span class="name">ting</span><span class="punctuation">)</span>
<span class="keyword">print</span> <span class="name">ling</span><span class="operator">.</span><span class="name">addAllNums</span><span class="punctuation">()</span>
</pre>
<ul class="simple">
<li><strong>composition</strong>: is similar to the aggregation, but only incorporating a specific version of the subclass.</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">A</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">a</span><span class="punctuation">,</span> <span class="name">b</span><span class="punctuation">,</span> <span class="name">c</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">a</span> <span class="operator">=</span> <span class="name">a</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">b</span> <span class="operator">=</span> <span class="name">b</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">c</span> <span class="operator">=</span> <span class="name">c</span>
<span class="keyword">def</span> <span class="name function">addNums</span><span class="punctuation">():</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">b</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">c</span>
<span class="keyword">class</span> <span class="name class">B</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">d</span><span class="punctuation">,</span> <span class="name">e</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">d</span> <span class="operator">=</span> <span class="name">d</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">e</span> <span class="operator">=</span> <span class="name">e</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">A</span> <span class="operator">=</span> <span class="name">A</span><span class="punctuation">(</span><span class="literal string">"yo"</span><span class="punctuation">,</span> <span class="literal number integer">2</span><span class="punctuation">,</span> <span class="literal number integer">6</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">addAllNums</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name">x</span> <span class="operator">=</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">d</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">e</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">A</span><span class="operator">.</span><span class="name">b</span> <span class="operator">+</span> <span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">A</span><span class="operator">.</span><span class="name">c</span>
<span class="keyword">return</span> <span class="name">x</span>
<span class="name">ling</span> <span class="operator">=</span> <span class="name">B</span><span class="punctuation">(</span><span class="literal number integer">5</span><span class="punctuation">,</span> <span class="literal number integer">9</span><span class="punctuation">)</span>
<span class="keyword">print</span> <span class="name">ling</span><span class="operator">.</span><span class="name">addAllNums</span><span class="punctuation">()</span>
</pre>
<pre class="literal-block">
Remember: those "association/combination" names may vary in the literature.
</pre>
</div>
<div class="section" id="encapsulation-and-polymorphism">
<h1><a class="toc-backref" href="#id6">Encapsulation and polymorphism</a></h1>
<ul class="simple">
<li><strong>encapsulation</strong>: In an object oriented program, one can restrict access to methods and attributes.</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">C</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">a</span> <span class="operator">=</span> <span class="literal number integer">1</span> <span class="comment"># OK to access directly</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">_a</span> <span class="operator">=</span> <span class="literal number integer">2</span> <span class="comment"># should be considered private</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">__a</span> <span class="operator">=</span> <span class="literal number integer">3</span> <span class="comment"># considered private, name Disfigured</span>
</pre>
<pre class="literal-block">
Warning! Some people say that *encapsulation* can prevent the data from being modified. This is **not** the case in Python (and even Java[!]. Other methods need to used to avoid modification).
</pre>
<ul class="simple">
<li><strong>polymorphism</strong>: is the principle by which two or more classes can invoke methods that have the same identification (signature) but distinct, specialized behaviors for each one.</li>
</ul>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">Person</span><span class="punctuation">(</span><span class="name builtin">object</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">pay_bill</span><span class="punctuation">():</span>
<span class="keyword">raise</span> <span class="name exception">NotImplementedError</span>
<span class="keyword">class</span> <span class="name class">Millionare</span><span class="punctuation">(</span><span class="name">Person</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">pay_bill</span><span class="punctuation">():</span>
<span class="keyword">print</span> <span class="literal string">"Here you go! Keep the change!"</span>
<span class="keyword">class</span> <span class="name class">GradStudent</span><span class="punctuation">(</span><span class="name">Person</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">pay_bill</span><span class="punctuation">():</span>
<span class="keyword">print</span> <span class="literal string">"Can I owe you ten bucks or do the dishes?"</span>
</pre>
<!-- There are four types of polymorphism that a programming language may have (note that not every object-oriented language has implemented all types of polymorphism): -->
<ul class="simple">
<li><strong>interface</strong>: is a contract between the class and the outside world. When a class contemplates/implements an interface, it is committed to providing the behavior expected by the interface.</li>
<li><strong>packages</strong> (or <strong>namespaces</strong>) are references for class/interface organization.</li>
</ul>
<pre class="code python literal-block">
<span class="keyword namespace">import</span> <span class="name namespace">scipy</span>
<span class="name">scipy</span><span class="operator">.</span><span class="name">interpolate</span>
<span class="name">scipy</span><span class="operator">.</span><span class="name">interpolate</span><span class="operator">.</span><span class="name">quad</span>
<span class="name">scipy</span><span class="operator">.</span><span class="name">integrate</span>
</pre>
</div>
<div class="section" id="other-oop-concepts">
<h1><a class="toc-backref" href="#id7">Other OOP Concepts</a></h1>
<ul class="simple">
<li><strong>ducktyping</strong> (or duck typing)</li>
</ul>
<p>As far as the function <tt class="docutils literal">in_the_forest</tt> is concerned, the <tt class="docutils literal">Person</tt> object is a <em>duck</em>:</p>
<pre class="code python literal-block">
<span class="keyword">class</span> <span class="name class">Duck</span><span class="punctuation">:</span>
<span class="keyword">def</span> <span class="name function">quack</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">"Quaaaaaack!"</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">feathers</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">"The duck has white and gray feathers."</span><span class="punctuation">)</span>
<span class="keyword">class</span> <span class="name class">Person</span><span class="punctuation">:</span>
<span class="keyword">def</span> <span class="name function">quack</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">"The person imitates a duck."</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">feathers</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">"The person takes a feather from the ground and shows it."</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">name</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">print</span><span class="punctuation">(</span><span class="literal string">"John Smith"</span><span class="punctuation">)</span>
<span class="keyword">def</span> <span class="name function">in_the_forest</span><span class="punctuation">(</span><span class="name">duck</span><span class="punctuation">):</span>
<span class="name">duck</span><span class="operator">.</span><span class="name">quack</span><span class="punctuation">()</span>
<span class="name">duck</span><span class="operator">.</span><span class="name">feathers</span><span class="punctuation">()</span>
<span class="keyword">def</span> <span class="name function">game</span><span class="punctuation">():</span>
<span class="name">donald</span> <span class="operator">=</span> <span class="name">Duck</span><span class="punctuation">()</span>
<span class="name">john</span> <span class="operator">=</span> <span class="name">Person</span><span class="punctuation">()</span>
<span class="name">in_the_forest</span><span class="punctuation">(</span><span class="name">donald</span><span class="punctuation">)</span>
<span class="name">in_the_forest</span><span class="punctuation">(</span><span class="name">john</span><span class="punctuation">)</span>
<span class="name">game</span><span class="punctuation">()</span>
</pre>
<ul class="simple">
<li><strong>message (passing)</strong> is the selection of the code to execute in response to a <strong>method call</strong>, typically by looking up the method in a table associated with the object. This feature is known as <strong>dynamic dispatch</strong>, and distinguishes an object from an <strong>abstract data type</strong>, which has a fixed (static) implementation of the operations for all instances. [<em>Not covered here</em>]</li>
</ul>
</div>
<div class="section" id="oop-pro-et-contra">
<h1><a class="toc-backref" href="#id8">OOP pro et contra</a></h1>
<p>Advantages of OOP:</p>
<ul class="simple">
<li>A more logical and better encapsulated code division.</li>
<li>This makes maintaining and extending the code easier and with less risk of inserting bugs.</li>
<li>It is also easier to reuse the code.</li>
<li>It is easier to manage the development of this type of software when we have a large team.</li>
</ul>
<p>Disadvantages of OOP</p>
<ul class="simple">
<li>Learning of the object-oriented programming paradigm is more complicated. In traditional procedural programming, just decorate a few dozen commands and you can already make a simple program.</li>
<li>Hardly an object-oriented language will be able to run over non-object-oriented languages.</li>
</ul>
</div>
<div class="section" id="extra">
<h1><a class="toc-backref" href="#id9">Extra</a></h1>
<ul class="simple">
<li><strong>UML</strong> (Unified Modeling Language) is a general-purpose, developmental, modeling language in the field of software engineering, that is intended to provide a standard way to visualize the design of a system.</li>
<li><strong>SysML</strong> (Systems Modeling Language) can be seen as a <em>system view</em> of the application, or as an extension of subsets of UML.</li>
</ul>
<p>This kind of tools can be used, for example, together with <strong>abstraction</strong> level concepts for automatic programming (or automatic coding)!</p>
</div>
<div class="section" id="exercises">
<h1><a class="toc-backref" href="#id10">Exercises</a></h1>
<ol class="arabic simple">
<li>What <tt class="docutils literal">dir()</tt> do?</li>
<li>What <tt class="docutils literal"><span class="pre">hasattr(),</span> <span class="pre">getattr(),</span> setattr()</tt> and <tt class="docutils literal">delattr()</tt> do?</li>
<li>What is happening here?</li>
</ol>
<pre class="code literal-block">
class test:
def __init__(self):
print "init 1"
def __init__(self):
print "init 2"
</pre>
<ol class="arabic simple">
<li>How can you change a class (global) attribute?</li>
<li>What <tt class="docutils literal">isinstance(variable, class)</tt> do?</li>
<li>Is <tt class="docutils literal">Lassie</tt> an instance of <tt class="docutils literal">Pets</tt> or <tt class="docutils literal">Toys</tt>?</li>
<li>What <tt class="docutils literal">instance.__base__</tt> do?</li>
<li>About <strong>interfaces</strong>. Understand what is happening here:</li>
</ol>
<pre class="code python literal-block">
<span class="literal string doc">"""http://python-3-patterns-idioms-test.readthedocs.io/en/latest/ChangeInterface.html"""</span>
<span class="keyword">class</span> <span class="name class">WhatIHave</span><span class="punctuation">:</span>
<span class="keyword">def</span> <span class="name function">g</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span> <span class="keyword">pass</span>
<span class="keyword">def</span> <span class="name function">h</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span> <span class="keyword">pass</span>
<span class="keyword">class</span> <span class="name class">WhatIWant</span><span class="punctuation">:</span>
<span class="keyword">def</span> <span class="name function">f</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span> <span class="keyword">pass</span>
<span class="keyword">class</span> <span class="name class">ProxyAdapter</span><span class="punctuation">(</span><span class="name">WhatIWant</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">whatIHave</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">whatIHave</span> <span class="operator">=</span> <span class="name">whatIHave</span>
<span class="keyword">def</span> <span class="name function">f</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="comment"># Implement behavior using</span>
<span class="comment"># methods in WhatIHave:</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">whatIHave</span><span class="operator">.</span><span class="name">g</span><span class="punctuation">()</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">whatIHave</span><span class="operator">.</span><span class="name">h</span><span class="punctuation">()</span>
<span class="keyword">class</span> <span class="name class">WhatIUse</span><span class="punctuation">:</span>
<span class="keyword">def</span> <span class="name function">op</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">whatIWant</span><span class="punctuation">):</span>
<span class="name">whatIWant</span><span class="operator">.</span><span class="name">f</span><span class="punctuation">()</span>
<span class="comment"># Approach 2: build adapter use into op():</span>
<span class="keyword">class</span> <span class="name class">WhatIUse2</span><span class="punctuation">(</span><span class="name">WhatIUse</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">op</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">whatIHave</span><span class="punctuation">):</span>
<span class="name">ProxyAdapter</span><span class="punctuation">(</span><span class="name">whatIHave</span><span class="punctuation">)</span><span class="operator">.</span><span class="name">f</span><span class="punctuation">()</span>
<span class="comment"># Approach 3: build adapter into WhatIHave:</span>
<span class="keyword">class</span> <span class="name class">WhatIHave2</span><span class="punctuation">(</span><span class="name">WhatIHave</span><span class="punctuation">,</span> <span class="name">WhatIWant</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">f</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">g</span><span class="punctuation">()</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">h</span><span class="punctuation">()</span>
<span class="comment"># Approach 4: use an inner class:</span>
<span class="keyword">class</span> <span class="name class">WhatIHave3</span><span class="punctuation">(</span><span class="name">WhatIHave</span><span class="punctuation">):</span>
<span class="keyword">class</span> <span class="name class">InnerAdapter</span><span class="punctuation">(</span><span class="name">WhatIWant</span><span class="punctuation">):</span>
<span class="keyword">def</span> <span class="name function">__init__</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">,</span> <span class="name">outer</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">outer</span> <span class="operator">=</span> <span class="name">outer</span>
<span class="keyword">def</span> <span class="name function">f</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">outer</span><span class="operator">.</span><span class="name">g</span><span class="punctuation">()</span>
<span class="name builtin pseudo">self</span><span class="operator">.</span><span class="name">outer</span><span class="operator">.</span><span class="name">h</span><span class="punctuation">()</span>
<span class="keyword">def</span> <span class="name function">whatIWant</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">):</span>
<span class="keyword">return</span> <span class="name">WhatIHave3</span><span class="operator">.</span><span class="name">InnerAdapter</span><span class="punctuation">(</span><span class="name builtin pseudo">self</span><span class="punctuation">)</span>
<span class="name">whatIUse</span> <span class="operator">=</span> <span class="name">WhatIUse</span><span class="punctuation">()</span>
<span class="name">whatIHave</span> <span class="operator">=</span> <span class="name">WhatIHave</span><span class="punctuation">()</span>
<span class="name">adapt</span><span class="operator">=</span> <span class="name">ProxyAdapter</span><span class="punctuation">(</span><span class="name">whatIHave</span><span class="punctuation">)</span>
<span class="name">whatIUse2</span> <span class="operator">=</span> <span class="name">WhatIUse2</span><span class="punctuation">()</span>
<span class="name">whatIHave2</span> <span class="operator">=</span> <span class="name">WhatIHave2</span><span class="punctuation">()</span>
<span class="name">whatIHave3</span> <span class="operator">=</span> <span class="name">WhatIHave3</span><span class="punctuation">()</span>
<span class="name">whatIUse</span><span class="operator">.</span><span class="name">op</span><span class="punctuation">(</span><span class="name">adapt</span><span class="punctuation">)</span>
<span class="comment"># Approach 2:</span>
<span class="name">whatIUse2</span><span class="operator">.</span><span class="name">op</span><span class="punctuation">(</span><span class="name">whatIHave</span><span class="punctuation">)</span>
<span class="comment"># Approach 3:</span>
<span class="name">whatIUse</span><span class="operator">.</span><span class="name">op</span><span class="punctuation">(</span><span class="name">whatIHave2</span><span class="punctuation">)</span>
<span class="comment"># Approach 4:</span>
<span class="name">whatIUse</span><span class="operator">.</span><span class="name">op</span><span class="punctuation">(</span><span class="name">whatIHave3</span><span class="operator">.</span><span class="name">whatIWant</span><span class="punctuation">())</span>
</pre>
</div>
</div>
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