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<div class="section" id="python-objects-or-what-s-with-the-periods-everywhere">

<h1>Python Objects - or what&#8217;s with the periods everywhere?<a class="headerlink" href="#python-objects-or-what-s-with-the-periods-everywhere" title="Permalink to this headline">¶</a></h1>

<p>Most things in Python are objects. But what is an object?</p>

<p>Every constant, variable, or function in Python is actually a object with a

type and associated attributes and methods. An <em>attribute</em> a property of

the object that you get or set by giving the &lt;object_name&gt; + dot +

&lt;attribute_name&gt;, for example <code class="docutils literal"><span class="pre">img.shape</span></code>. A <em>method</em> is a function

that the object provides, for example <code class="docutils literal"><span class="pre">img.argmax(axis=0)</span></code> or <code class="docutils literal"><span class="pre">img.min()</span></code>.</p>

<p>Use tab completion in IPython to inspect objects and start to understand

attributes and methods. To start off create a list of 4 numbers:</p>

<div class="highlight-python"><div class="highlight"><pre><span></span>a = [3, 1, 2, 1]

a.&lt;TAB&gt;

<p>This will show the available attributes and methods for the Python list

<code class="docutils literal"><span class="pre">a</span></code>. <strong>Using &lt;TAB&gt;-completion and help is a very efficient way to learn and later

remember object methods!</strong></p>

<div class="highlight-python"><div class="highlight"><pre><span></span>In [17]: a.&lt;TAB&gt;

a.append a.extend a.insert a.remove a.sort

a.count a.index a.pop a.reverse

<p>Here you see useful looking functions like <code class="docutils literal"><span class="pre">append</span></code> or <code class="docutils literal"><span class="pre">sort</span></code> which

you can get help for and use:</p>

<div class="highlight-python"><div class="highlight"><pre><span></span>a.sort

a.sort?

a.sort()

a

<p>You can tell the difference between an attribute and a callable method with

the callable function:</p>

<div class="highlight-python"><div class="highlight"><pre><span></span><span class="nb">callable</span><span class="p">(</span><span class="n">a</span><span class="o">.</span><span class="n">sort</span><span class="p">)</span>

<span class="p">[</span><span class="n">x</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">dir</span><span class="p">(</span><span class="n">a</span><span class="p">)</span> <span class="k">if</span> <span class="nb">callable</span><span class="p">(</span><span class="nb">getattr</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">x</span><span class="p">))</span> <span class="ow">and</span> <span class="ow">not</span> <span class="n">x</span><span class="o">.</span><span class="n">startswith</span><span class="p">(</span><span class="s1">&#39;__&#39;</span><span class="p">)]</span>

<p><em>Mention classes and objects as class instances?</em></p>

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