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<h1 style="margin-bottom:0;padding-bottom:0;">Doing Python OOP the wrong way</h1>
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<em>In the name of science!</em>
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<br><br>
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<p>If you know me, you probably know of the many weird things I do with python. Most recent of which being this <a rel="noopener" target="_blank" href="https://en.wikipedia.org/wiki/Fizz_buzz">FizzBuzz</a> implementation in one line of python code:</p>
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span style="color:#bf616a;">_</span><span>=[</span><span style="color:#96b5b4;">print</span><span>("</span><span style="color:#a3be8c;">FizzBuzz</span><span>"[</span><span style="color:#bf616a;">_</span><span>*</span><span style="color:#bf616a;">_</span><span>%</span><span style="color:#d08770;">3</span><span>*</span><span style="color:#d08770;">4</span><span>:</span><span style="color:#d08770;">8</span><span>--</span><span style="color:#bf616a;">_</span><span>**</span><span style="color:#d08770;">4</span><span>%</span><span style="color:#d08770;">5</span><span>] or </span><span style="color:#bf616a;">_</span><span>) </span><span style="color:#b48ead;">for </span><span style="color:#bf616a;">_ </span><span style="color:#b48ead;">in </span><span style="color:#96b5b4;">range</span><span>(</span><span style="color:#d08770;">101</span><span>)]
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</span></code></pre>
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<p>This installment of "weird things I do with python" will not focus on one-liners (that's going on my todo list though). But instead, playing with Python's classes and object system.</p>
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<h2 id="a-quick-introduction-to-classes">A quick introduction to classes</h2>
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<p>Im going to assume that you, the reader, have some reasonable knowledge of how computers work, and OOP concepts. If you do not, there are <a rel="noopener" target="_blank" href="https://medium.com/swlh/5-free-object-oriented-programming-online-courses-for-programmers-156afd0a3a73">many great online resources</a> to help you out.</p>
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<p>As a quick refresher, this is the Python syntax for a basic class:</p>
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span style="color:#b48ead;">class </span><span style="color:#ebcb8b;">MyClass</span><span style="color:#eff1f5;">:
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</span><span>
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</span><span> </span><span style="color:#65737e;"># This is the constructor. __init__ is an overridable python built-in
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</span><span> </span><span style="color:#b48ead;">def </span><span style="color:#96b5b4;">__init__</span><span>(</span><span style="color:#bf616a;">self</span><span>, </span><span style="color:#bf616a;">arg1</span><span>: int):
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</span><span>
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</span><span> </span><span style="color:#65737e;"># Here we set the class' scoped my_number to arg1
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</span><span> </span><span style="color:#bf616a;">self</span><span>.my_number = arg1
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</span><span>
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</span><span> </span><span style="color:#b48ead;">def </span><span style="color:#8fa1b3;">printMyNumber</span><span>(</span><span style="color:#bf616a;">self</span><span>):
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</span><span> </span><span style="color:#96b5b4;">print</span><span>(</span><span style="color:#bf616a;">self</span><span>.my_number)
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</span></code></pre>
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<p>This is really just a fancy setter and getter. Here is some example usage:</p>
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span>my_object = </span><span style="color:#bf616a;">MyClass</span><span>(</span><span style="color:#d08770;">10</span><span>)
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</span><span>my_object.</span><span style="color:#bf616a;">printMyNumber</span><span>() </span><span style="color:#65737e;"># Prints 10
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</span></code></pre>
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<h2 id="noticing-something-odd">Noticing something odd</h2>
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<p>Before reading the following, keep in mind that (as of now) I have not actually looked at the Python interpreter's source code enough to know about their memory system. The following is just an educated guess.</p>
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<p>Looking at any python class, you may notice that <strong>at least</strong> 1 argument is required. <code>self</code> is used to access the class' data from itself. This is not present in most other languages I know, which means there might be something interesting happening behind the scenes. Here is a re-implementation of <code>MyClass</code> from above in java:</p>
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<pre data-lang="java" style="background-color:#2b303b;color:#c0c5ce;" class="language-java "><code class="language-java" data-lang="java"><span style="color:#b48ead;">public class </span><span style="color:#ebcb8b;">MyClass </span><span style="color:#eff1f5;">{
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</span><span style="color:#eff1f5;"> </span><span style="color:#b48ead;">int </span><span style="color:#eff1f5;">my_int;
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</span><span style="color:#eff1f5;">
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</span><span style="color:#eff1f5;"> </span><span style="color:#b48ead;">public </span><span style="color:#8fa1b3;">MyClass</span><span style="color:#eff1f5;">(</span><span style="color:#b48ead;">int </span><span style="color:#bf616a;">arg1</span><span style="color:#eff1f5;">){
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</span><span style="color:#eff1f5;"> my_int </span><span>=</span><span style="color:#eff1f5;"> arg1;
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</span><span style="color:#eff1f5;"> }
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</span><span style="color:#eff1f5;">
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</span><span style="color:#eff1f5;"> </span><span style="color:#b48ead;">public void </span><span style="color:#8fa1b3;">printMyNumber</span><span style="color:#eff1f5;">(){
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</span><span style="color:#eff1f5;"> </span><span style="color:#ebcb8b;">System</span><span style="color:#eff1f5;">.out.</span><span style="color:#bf616a;">println</span><span style="color:#eff1f5;">(my_int);
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</span><span style="color:#eff1f5;"> }
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</span><span style="color:#eff1f5;">}
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</span></code></pre>
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<p>Notice the fact that there is no <code>self</code>? Yet Java methods can still access class data.</p>
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<h2 id="implementing-objects-in-a-non-object-oriented-language">Implementing objects in a non-object oriented language</h2>
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<p>In a non-OOP language (like C), objects can be faked by creating <a rel="noopener" target="_blank" href="https://en.wikipedia.org/wiki/Struct_(C_programming_language)">structures</a> and some standard functions. These functions then take a pointer to their "parent" structure. Confusing? yes. But it works, and I see it used all over the place. Here a pseudocode example:</p>
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<pre style="background-color:#2b303b;color:#c0c5ce;"><code><span>struct MyClass {
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</span><span> int my_int; // Scpoed int
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</span><span>}
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</span><span>
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</span><span>fn printMyNumber(MyClass* self){
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</span><span> print(self.my_int);
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</span><span>}
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</span><span>
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</span></code></pre>
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<p><code>printMyNumber</code> takes a pointer to it's "parent class", called <code>self</code>. Look familiar? This is how Python works.</p>
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<h2 id="let-s-do-some-python">Let's do some Python</h2>
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<p>Alright.. Time for some "broken" Python. Here is yet another implementation of <code>MyClass</code>, except this time, each function is globally scoped:</p>
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<pre data-lang="python" style="background-color:#2b303b;color:#c0c5ce;" class="language-python "><code class="language-python" data-lang="python"><span>
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</span><span style="color:#65737e;"># Private, globally scoped functions
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</span><span style="color:#b48ead;">def </span><span style="color:#8fa1b3;">_init_myclass</span><span>(</span><span style="color:#bf616a;">self</span><span>, </span><span style="color:#bf616a;">arg1</span><span>: int):
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</span><span> </span><span style="color:#bf616a;">self</span><span>.my_number = arg1
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</span><span>
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</span><span style="color:#b48ead;">def </span><span style="color:#8fa1b3;">_myclass_printMyNumber</span><span>(</span><span style="color:#bf616a;">self</span><span>):
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</span><span> </span><span style="color:#96b5b4;">print</span><span>(</span><span style="color:#bf616a;">self</span><span>.my_number)
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</span><span>
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</span><span>
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</span><span style="color:#65737e;"># struct-like class containing function pointers
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</span><span style="color:#b48ead;">class </span><span style="color:#ebcb8b;">MyClass</span><span style="color:#eff1f5;">:
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</span><span>
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</span><span> </span><span style="color:#96b5b4;">__init__ </span><span>= _init_myclass
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</span><span> printMyNumber = _myclass_printMyNumber
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</span><span>
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</span></code></pre>
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<p>This code will still function like a normal class. Unlike a regular class definition, the above code defines the constructor and <code>printMyNumber</code> methods in the global scope (marked as private with an underscore). A class is then created with function pointers to each of the global functions. This means that calling <code>MyClass.printMyNumber</code> will point to, and execute <code>_myclass_printMyNumber</code>. The interpreter still treats the underscore functions as members of <code>MyClass</code>, and passes the <code>self</code> argument along to them.</p>
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<h2 id="why">Why?</h2>
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<p>I have absolutely no idea why this would ever be useful. If you think you should start doing this in your code, <strong>don't</strong>. It leads to very messy and confusing code, and is bad practice in just about every way. </p>
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<p>The point of this post is to show yet another instance of the Python interpreter saying "<a rel="noopener" target="_blank" href="https://www.urbandictionary.com/define.php?term=idgaf">idgaf</a>", and letting us have a little fun.</p>
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