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<h1 id="python-classes">Python Classes</h1>
<p>Python is an <a href="https://en.wikipedia.org/wiki/Object-oriented_programming">Object Oriented Programming</a> (OOP) language. In Python, <a href="https://docs.python.org/3/tutorial/classes.html">classes</a> are used to represent a logical collection of fields and methods. Further, these classes are utilized to create objects.</p>
<p>In this article, learn how to create and use a Python class.</p>
<h2 id="what-is-a-class">What is a class?</h2>
<p>A class is a logical template to represent objects. In addition to functions or methods that perform related operations, a class can contain properties that represent state. Objects are instances of such classes representing one or more entities. The process of creating an object from a class is called instantiation. A single class can be instantiated several times representing several objects.</p>
<h4 id="example">Example</h4>
<p>Consider a class <code>PersonInformation</code> representing information of a person. <code>PersonInformation</code> class may contain personal details like <code>first_name</code>, <code>last_name</code>, <code>age</code> as fields and may include functions such as <code>print_data()</code> to print the information stored in those fields. Each person's details are stored in a single instance of the class.</p>
<h2 id="class-definition">Class definition</h2>
<p>A class is created using the keyword <code>class</code>.</p>
<h3 id="syntax">Syntax</h3>
<pre class="hljs"><code><div><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">ClassName</span>:</span>
<span class="hljs-string">''' This is a docstring which briefly describes the class.'''</span>
<span class="hljs-comment"># fields</span>
<span class="hljs-comment"># functions</span>
<span class="hljs-comment"># more code</span>
</div></code></pre>
<h5 id="note">Note:</h5>
<ul>
<li>Class names are written in <a href="https://en.wikipedia.org/wiki/Camel_case">camel case</a>
<ul>
<li><strong>Example</strong>: <code>ClassName</code>, <code>PersonInformation</code>, <code>Country</code>, <code>TechnicalWriter</code>.</li>
</ul>
</li>
<li>Fields and methods are written in <a href="https://en.wikipedia.org/wiki/Snake_case">snake_case</a>.</li>
<li>A class may contain blocks of code representing functions or fields.</li>
<li>Its recommended to include a docstring in the beginning, which briefly describes the class's functionality.</li>
<li>You can also create a class without any statements. However, such a class is of less use.</li>
</ul>
<h3 id="sample">Sample</h3>
<pre class="hljs"><code><div><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PersonInformation</span>
# <span class="hljs-title">List</span> <span class="hljs-title">of</span> <span class="hljs-title">statements</span>
</span></div></code></pre>
<p>A class creates a new local <code>namespace</code> where all its attributes are defined.</p>
<h2 id="defining-class-attributes">Defining class attributes</h2>
<p>In a class, class attributes are fields defined outside the methods. They are shared across instances of the class in the same process.</p>
<h3 id="sample">Sample</h3>
<pre class="hljs"><code><div><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PersonInformation</span>:</span>
first_name = <span class="hljs-string">"Alex"</span>
last_name = <span class="hljs-string">"Sa"</span>
age = <span class="hljs-number">10</span>
</div></code></pre>
<h3 id="special-attributes">Special attributes</h3>
<p>There can also be special attributes that begin with double underscores <code>__</code>.</p>
<h4 id="example">Example</h4>
<ul>
<li><code> __doc__</code> gives docstring of the class.</li>
<li><code>__init__()</code> is the constructor of the class.</li>
<li><code>__str__()</code> return human-readable representation of the class.</li>
</ul>
<h2 id="creating-an-object">Creating an object</h2>
<p>Once a class is defined, you can create an object by instantiating it. Object creation is similar to a function call.</p>
<h3 id="syntax">Syntax</h3>
<pre class="hljs"><code><div>objectName = ClassName()
</div></code></pre>
<p>This creates a new object instance, <code>objectName</code>, which can be used to access the attributes.</p>
<h3 id="sample">Sample</h3>
<pre class="hljs"><code><div>person_information_object = PersonInformation()
print(PersonInformation.first_name)
</div></code></pre>
<h3 id="output">Output</h3>
<pre class="hljs"><code><div>Alex
</div></code></pre>
<h2 id="defining-class-methods">Defining class methods</h2>
<p>Methods are functions you can define to access, modify and perform operations on these attributes.</p>
<h3 id="syntax">Syntax</h3>
<pre class="hljs"><code><div><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">ClassName</span>:</span>
<span class="hljs-string">''' This is a docstring which briefly describes the class.'''</span>
<span class="hljs-comment"># variables</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, argument <span class="hljs-number">1</span>, ..., argument n)</span>:</span>
<span class="hljs-comment"># more code</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">function_name</span><span class="hljs-params">(self, argument <span class="hljs-number">1</span>, ..., argument n)</span>:</span>
<span class="hljs-comment"># more code</span>
</div></code></pre>
<h3 id="self-parameter"><code>self</code> parameter</h3>
<ul>
<li>The <code>self</code> parameter is the first parameter of any instance-level method. It's name is written in snake case by convention.</li>
<li>Its a reference to the current instance of the class and is used to access instance attributes or methods. It can also be used to refer to class-level attributes or methods.</li>
</ul>
<h3 id="init-function"><code>__init__()</code> function</h3>
<p>All classes have a built-in function <code>__int__()</code> that automatically executes when a class is initiated. You can use this function to assign values to class attributes at runtime. This type of function is known as a constructor in OOP.</p>
<p>Let's use the above <a href="#sample-1">sample code</a> with <code>__init__()</code> and a method.</p>
<h3 id="sample---try-this">Sample - <a href="https://replit.com/@AlekhyaSasi/Person-information-class?lite=true#main.py">Try this</a></h3>
<pre class="hljs"><code><div><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">PersonInformation</span>:</span>
<span class="hljs-string">''' This is a class with personal information such as first name, last name, and age.'''</span>
<span class="hljs-comment"># Define an init method with variables to obtain values at runtime.</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, first_name, last_name, age)</span>:</span>
self.first_name = first_name
self.last_name = last_name
self.age = age
<span class="hljs-comment"># Define a method to display the values.</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">print_data</span><span class="hljs-params">(self)</span>:</span>
print(<span class="hljs-string">"Person information:"</span>)
print(<span class="hljs-string">f'Name: <span class="hljs-subst">{self.first_name}</span> <span class="hljs-subst">{self.last_name}</span>'</span>)
print(<span class="hljs-string">f'Age: <span class="hljs-subst">{self.age}</span>'</span>)
<span class="hljs-comment"># Intializing an object.</span>
person_information = PersonInformation(<span class="hljs-string">"Alex"</span>, <span class="hljs-string">"Sa"</span>, <span class="hljs-number">10</span>)
person_information.print_data()
</div></code></pre>
<h3 id="output">Output</h3>
<pre class="hljs"><code><div>Person information:
Name: Alex Sa
Age: 10
</div></code></pre>
<h2 id="conclusion">Conclusion</h2>
<p>In this article, you can learn the basic concepts of classes in Python. You can also view code samples to write a class containing methods.</p>
<p>Stay tuned for more informative articles.</p>
</body>
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