sec-attribute.ptx

<?xml version="1.0" encoding="UTF-8"?>

<!--*****************************************
This is part of Basic Programming
Copyright (C) 2024
Phạm Công Vinh
See the file COPYING for copying conditions.
******************************************-->

<section xml:id="sec-attribute" xmlns:xi="http://www.w3.org/2001/XInclude">
  <title>Attributes</title>

  <objectives>
    <ul>
      <li>Learn about attributes and how to access them.</li>
    </ul>
  </objectives>
  
  <definition xml:id="def-attribute">
    <idx><h>Definitions</h><h>of attributes</h></idx>
    <statement>
      <p>
        An <term>attribute</term> is a built-in variable storing <em>descriptive information</em> regarding another piece of data. In other words, it's metadata.
      </p>
      <p>
        Every data type has its own set of attributes.
      </p>
      <p>
        The attributes of a piece of data are <em>automatically updated</em> when said data is updated.
      </p>
    </statement>
  </definition>

  <technology>
    <title>Accessing an attribute</title>
    <idx><h>Syntax</h><h>of accessing attributes</h></idx>
    <p>
      <me>\text{data} . \! {\color{blue} \text{attribute's name}}</me>
    </p>
  </technology>

  <p>
    To demonstrate attributes, the following example makes use of an external data structure<mdash />a matrix imported from the external library Numpy (which you don't have to fully understand):
  </p>

  <aside>
    <title>Topic(s) you might be interested in</title>
    <p>
      <ul>
        <li>
          <p>
            <idx><h>Links</h><h>Python libraries</h></idx>
            <url href="https://www.google.com/search?q=what+is+a+Python+library" visual="google.com/search?q=what+is+a+Python+library">"what is a Python library"</url>
          </p>
        </li>
        <li>
          <p>
            <idx><h>Links</h><h>Numpy</h></idx>
            <url href="https://www.google.com/search?q=what+is+Numpy" visual="google.com/search?q=what+is+Numpy">"what is Numpy"</url>
          </p>
        </li>
        <li>
          <p>
            <idx><h>Links</h><h>matrices</h></idx>
            <url href="https://www.google.com/search?q=what+is+a+matrix" visual="google.com/search?q=what+is+a+matrix">"what is a matrix"</url>
          </p>
        </li>
      </ul>
    </p> 
  </aside>

  <sage language="python">
    <input>
      import numpy as np # Use library Numpy

      mat = np.matrix([
        [1, 2, 3],
        [2, 4, 6]
      ])

      print(mat.size)
      print(mat.shape)
    </input>
  </sage>
  <problem>
    <pre>
      6
      (2, 3)
    </pre>
  </problem>
  <investigation>
    <idx><h>Code examples</h><h>accessing attributes</h></idx>
    <idx><h>Functions</h><h>np.matrix()</h></idx>
    <p></p>
    <p>
      <c>mat.size</c> returns the total number of elements of the matrix named <c>mat</c>.
    </p>
    <p>
      <c>mat.shape</c> returns the number of rows and columns of the matrix respectively.
    </p>
  </investigation>

  <p>
    However, the data type <c>int</c>, for example, does not have such attributes:
  </p>

  <sage language="python">
    <input>
      a = 5
      print(a.size)
    </input>
  </sage>
  <problem>
    <pre>
      AttributeError
      Cell In [1], line 2

      ...

      AttributeError: 'int' object has no attribute 'size'
    </pre>
  </problem>
  <investigation>
    <idx><h>Code examples</h><h>accessing invalid attribute</h></idx>
    <p></p>
    <p>
      As the error states.
    </p>
  </investigation>
  
  <p>
    <cd>
    </cd>
  </p>

  <exploration>
    <title>Basic Programming <mdash /> Part 9: Attributes</title>
    <idx><h>Videos</h><h>part 09</h></idx>
  
    <p>
      Coming soon.
    </p>
    
    <video youtubeplaylist="PLBLdRr-v59vwnKvmvLtcgmAnsb2K1Ta_M" />
    
  </exploration>

</section>