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<!DOCTYPE html>
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<li class="toctree-l1"><a class="reference internal" href="../intro.html">Python Like You Mean It</a></li>
<li class="toctree-l1 current"><a class="reference internal" href="../module_1.html">Module 1: Getting Started with Python</a><ul class="current">
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<li class="toctree-l2"><a class="reference internal" href="GettingStartedWithPython.html">Introducing the Python Programming Language</a></li>
<li class="toctree-l2"><a class="reference internal" href="Installing_Python.html">Installing Python</a></li>
<li class="toctree-l2 current"><a class="current reference internal" href="#">An Informal Introduction to Python</a><ul>
<li class="toctree-l3"><a class="reference internal" href="#Dabbling-with-Numbers">Dabbling with Numbers</a></li>
<li class="toctree-l3"><a class="reference internal" href="#Messing-with-Strings">Messing with Strings</a></li>
<li class="toctree-l3"><a class="reference internal" href="#Playing-with-Lists">Playing with Lists</a></li>
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<li class="toctree-l1"><a class="reference internal" href="../module_3.html">Module 3: The Essentials of NumPy</a></li>
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<div class="section" id="An-Informal-Introduction-to-Python">
<h1>An Informal Introduction to Python<a class="headerlink" href="#An-Informal-Introduction-to-Python" title="Permalink to this headline">¶</a></h1>
<p>Now that you have the Anaconda distribution of Python installed on your
machine, let’s write some simple Python code! We are going to forego
writing a full Python script for now, and instead make use of a
convenient tool for doing quick code scratchwork. The IPython console
was installed as a part of Anaconda; it will allow us build
incrementally off of snippets of code, instead of having to execute an
entire script all at once.</p>
<p>To start the IPython console, open your terminal (Mac/Linux) or
<code class="docutils literal"><span class="pre">cmd.exe</span></code> (Windows), type <code class="docutils literal"><span class="pre">ipython</span></code> into it, and hit <code class="docutils literal"><span class="pre"><Enter></span></code>.
You should see the following display on your screen:</p>
<div class="figure" id="id1">
<img alt="IPython console example" src="../_images/ipython_0.PNG" />
<p class="caption"><span class="caption-text">IPython console example</span></p>
</div>
<p>We can type small pieces of Python code into this console, and then
simply hit <code class="docutils literal"><span class="pre"><Enter></span></code> to have the CPython interpreter execute our code
immediately within the IPython console!</p>
<p>Let’s acquaint ourselves with Python’s numbers, strings, and lists. In
doing so, we will learn about the Python standard library, and how to
make use of its modules, like the math module. IPython’s autocompletion
and documentation-display utilities will provide a nice means for
exploring the library and the functionality built into the different
types of Python objects. A quick glimpse at Python’s strings and lists
will hint at the common interface Python provides for working with
sequences of objects, while highlighting some of the nice features of
these all-important data types.</p>
<div class="section" id="Dabbling-with-Numbers">
<h2>Dabbling with Numbers<a class="headerlink" href="#Dabbling-with-Numbers" title="Permalink to this headline">¶</a></h2>
<p>Time to execute some Python code that performs simple arithmetic. Typing
<code class="docutils literal"><span class="pre">2</span> <span class="pre">+</span> <span class="pre">3</span></code> into the IPython console and hitting the <code class="docutils literal"><span class="pre"><ENTER></span></code> key, you
should see the following input and output in the console:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [1]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="mi">2</span> <span class="o">+</span> <span class="mi">3</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[1]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>5
</pre></div>
</div>
</div>
<p>This console session is persistent, meaning that we can define a
variable and then reference it in our code later on within this console
session. Let’s define the variable <code class="docutils literal"><span class="pre">x</span></code> and assign it to the integer
<code class="docutils literal"><span class="pre">10</span></code> (please follow along in the IPython console)</p>
<div class="nbinput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [2]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">x</span> <span class="o">=</span> <span class="mi">10</span>
</pre></div>
</div>
</div>
<p>We can check the contents of <code class="docutils literal"><span class="pre">x</span></code> in this console by simply entering
<code class="docutils literal"><span class="pre">x</span></code> in the next line and hitting <code class="docutils literal"><span class="pre"><ENTER></span></code>:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [3]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">x</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[3]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>10
</pre></div>
</div>
</div>
<p>Now, let’s use <code class="docutils literal"><span class="pre">x</span></code> in a quadratic equation <span class="math">\(x^{2} + 2x + 3\)</span>, and
compute this total.</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [4]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">x</span><span class="o">**</span><span class="mi">2</span> <span class="o">+</span> <span class="mi">2</span><span class="o">*</span><span class="n">x</span> <span class="o">+</span> <span class="mi">3</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[4]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>123
</pre></div>
</div>
</div>
<p>Python’s “standard library”, the various tools and functions that come
packaged as part of the core language, includes plenty of familiar
mathematical functions. As a matter of organization, Python stores these
mathematical functions away in a module named “math”. To make use of
this math module, we must import it into our code.</p>
<div class="nbinput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [5]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="kn">import</span> <span class="nn">math</span>
</pre></div>
</div>
</div>
<p>Having imported it, the term <code class="docutils literal"><span class="pre">math</span></code> now refers the math module in our
code. IPython provides a nice way for us see a list of all the functions
that are provided by the math module. To utilize this, type into the
console <code class="docutils literal"><span class="pre">math.</span></code> (note the trailing period) and then hit <code class="docutils literal"><span class="pre"><TAB></span></code>. You
should see this list appear:</p>
<div class="figure" id="id2">
<img alt="Displaying the contents of the math module" src="../_images/ipython_math.PNG" />
<p class="caption"><span class="caption-text">Displaying the contents of the math module</span></p>
</div>
<p>In general, hitting <code class="docutils literal"><span class="pre"><TAB></span></code> will cue IPython to try to autocomplete
code for you. This menu displays all the valid things that you could
type after <code class="docutils literal"><span class="pre">math.</span></code>. Looking at the functions starting with “s”, we see
<code class="docutils literal"><span class="pre">sqrt()</span></code>. This is the square root function. To see autocompletion in
action, type <code class="docutils literal"><span class="pre">math.sq</span></code> and then hit <code class="docutils literal"><span class="pre"><TAB></span></code>. You should see the code
autocomplete to <code class="docutils literal"><span class="pre">math.sqrt</span></code>.</p>
<p>Let’s use this function to compute <span class="math">\(\sqrt{100}\)</span>:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [6]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">math</span><span class="o">.</span><span class="n">sqrt</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[6]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>10.0
</pre></div>
</div>
</div>
<p>You might wonder why the result displayed as <code class="docutils literal"><span class="pre">10.0</span></code> and not simply as
<code class="docutils literal"><span class="pre">10</span></code>; in Module 2 we will see that these are two different <em>types</em> of
numbers in the Python language. The former is called a floating-point
number, indicating the presence of its decimal point, whereas the latter
is an integer. The <code class="docutils literal"><span class="pre">math.sqrt</span></code> function is defined such that it always
returns its results as floating-point numbers.</p>
<p>In the case that we want to make frequent use of a certain function from
the math module, it’d be nice to avoid having to type out the math
module prefix, <code class="docutils literal"><span class="pre">math.</span></code>, repeatedly. We can accomplish this by
importing an individual function from the math module. Let’s import the
factorial function from the math module.</p>
<div class="nbinput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [7]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="kn">from</span> <span class="nn">math</span> <span class="k">import</span> <span class="n">factorial</span>
</pre></div>
</div>
</div>
<p>We can now make use of the <code class="docutils literal"><span class="pre">factorial</span></code> function in our code. Recall
that 5-factorial is <span class="math">\(5! = 5\times 4\times 3\times 2\times 1 = 120\)</span></p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [8]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">factorial</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[8]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>120
</pre></div>
</div>
</div>
</div>
<div class="section" id="Messing-with-Strings">
<h2>Messing with Strings<a class="headerlink" href="#Messing-with-Strings" title="Permalink to this headline">¶</a></h2>
<p>In the context of code, written text is referred to as a string of
characters, or string for short. Python is an excellent language for
doing text-processing work as it provides many convenient, efficient
functions for working with strings.</p>
<p>To begin, we simply form a string by typing characters between quotation
marks:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [9]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="s2">"the cat in the hat"</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[9]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'the cat in the hat'
</pre></div>
</div>
</div>
<p>Single quotes also work:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [10]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="s1">'the dog in the sash'</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[10]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'the dog in the sash'
</pre></div>
</div>
</div>
<p>If you use single quotes to form a string, then that string is able to
contain the double-quote as a character (and vice versa):</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [11]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="s1">'He picked up the phone, "Hello? What do you want?" Bob was a rather impolite dude.'</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[11]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'He picked up the phone, "Hello? What do you want?" Bob was a rather impolite dude.'
</pre></div>
</div>
</div>
<p>There are designated special characters that allow us to affect the way
a string is formatted when it is printed to the string. For example, if
<code class="docutils literal"><span class="pre">\n</span></code> ever occurs in a string, it is treated as a single character that
indicates a line-break. This will only manifest if such a string is fed
to the built-in <code class="docutils literal"><span class="pre">print</span></code> function, which informs the computer to print
text to a user’s screen.</p>
<p>Let’s create a string that will display as three separate lines, when
printed to the screen.</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [12]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="nb">print</span><span class="p">(</span><span class="s2">"I like to talk to dogs.</span><span class="se">\n</span><span class="s2">I like to talk to cats.</span><span class="se">\n</span><span class="s2">What's my deal?"</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt empty docutils container">
</div>
<div class="output_area docutils container">
<div class="highlight"><pre>
I like to talk to dogs.
I like to talk to cats.
What's my deal?
</pre></div></div>
</div>
<p>Of course, strings are useful beyond merely containing text! Let’s
explore some ways to manipulate strings. First, we’ll write a string and
assign it to a variable named <code class="docutils literal"><span class="pre">sentence</span></code>:</p>
<div class="nbinput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [13]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">sentence</span> <span class="o">=</span> <span class="s2">"Who would have thought that we were robots all along?"</span>
</pre></div>
</div>
</div>
<p>Let’s see how many characters are in this string by checking the
“length” of this sequence of characters:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [14]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="nb">len</span><span class="p">(</span><span class="n">sentence</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[14]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>53
</pre></div>
</div>
</div>
<p>We can access the first 4 characters in the string, the last 6
characters, or a few characters in the middle by “slicing” the string:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [15]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">sentence</span><span class="p">[:</span><span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[15]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'Who '
</pre></div>
</div>
</div>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [16]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">sentence</span><span class="p">[</span><span class="o">-</span><span class="mi">6</span><span class="p">:]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[16]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'along?'
</pre></div>
</div>
</div>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [17]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">sentence</span><span class="p">[</span><span class="mi">5</span><span class="p">:</span><span class="mi">22</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[17]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'ould have thought'
</pre></div>
</div>
</div>
<p>We can also check to see if some other string is contained within our
string. Is the string <code class="docutils literal"><span class="pre">"robot"</span></code> contained within <code class="docutils literal"><span class="pre">sentence</span></code>?</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [18]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="s2">"robot"</span> <span class="ow">in</span> <span class="n">sentence</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[18]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>True
</pre></div>
</div>
</div>
<p>As a quick way to check out the built-in functions that strings have
available to them, we can make use of IPython’s autocompletion feature
once again. Type <code class="docutils literal"><span class="pre">sentence.</span></code> (including the trailing period) and then
hit <code class="docutils literal"><span class="pre"><TAB></span></code>. A menu of functions should appear as so:</p>
<div class="figure" id="id3">
<img alt="Built-in functions for a string" src="../_images/ipython_string.PNG" />
<p class="caption"><span class="caption-text">Built-in functions for a string</span></p>
</div>
<p>Let’s use the count function to tally the number of lowercase w’s in
<code class="docutils literal"><span class="pre">sentence</span></code></p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [16]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">sentence</span><span class="o">.</span><span class="n">count</span><span class="p">(</span><span class="s1">'w'</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[16]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>3
</pre></div>
</div>
</div>
<p>Let’s see what the replace function does. IPython provides a great
utility for looking up the documentation for a function by simply
putting two question marks after the function name. For example:</p>
<div class="figure" id="id4">
<img alt="Looking up documentation for a function" src="../_images/ipython_doc1.PNG" />
<p class="caption"><span class="caption-text">Looking up documentation for a function</span></p>
</div>
<p>Putting our newfound understanding of the string’s replace function,
let’s replace “robot” with “computer”:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [17]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">sentence</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s2">"robot"</span><span class="p">,</span> <span class="s2">"computer"</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[17]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>'Who would have thought that we were computers all along?'
</pre></div>
</div>
</div>
</div>
<div class="section" id="Playing-with-Lists">
<h2>Playing with Lists<a class="headerlink" href="#Playing-with-Lists" title="Permalink to this headline">¶</a></h2>
<p>A list is one of several types of containers that are built into
Python’s standard library. It can hold a sequence of Python objects. We
can create a list of numbers:</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [19]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="o">/</span><span class="mi">3</span><span class="p">,</span> <span class="mi">10</span><span class="o">*</span><span class="mi">2</span><span class="p">,</span> <span class="mi">7</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[19]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>[-1, 0.3333333333333333, 20, 6]
</pre></div>
</div>
</div>
<p>A list can contain any type of Python object; it can store a mix of
numbers, strings, other lists, and much more!</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [20]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="s2">"a"</span><span class="p">,</span> <span class="mf">0.5</span><span class="p">,</span> <span class="s2">"apple and orange"</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[20]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>[1, 2, 'a', 0.5, 'apple and orange']
</pre></div>
</div>
</div>
<p>You can join lists together, which is known as concatenation.</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [21]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span> <span class="o">+</span> <span class="p">[</span><span class="s2">"a"</span><span class="p">,</span> <span class="s2">"b"</span><span class="p">,</span> <span class="s2">"c"</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[21]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>[1, 2, 3, 'a', 'b', 'c']
</pre></div>
</div>
</div>
<p>Like a string, a list is sequential in nature and we can access the
items in a list by specifying its position in the sequence. This is
known as “indexing” the list; the index of the first item in a sequence
is always 0.</p>
<div class="nbinput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [10]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">my_list</span> <span class="o">=</span> <span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">20</span><span class="p">,</span> <span class="mi">30</span><span class="p">,</span> <span class="mi">40</span><span class="p">,</span> <span class="mi">50</span><span class="p">,</span> <span class="mi">60</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [11]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">my_list</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[11]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>10
</pre></div>
</div>
</div>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [12]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">my_list</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[12]:
</pre></div>
</div>
<div class="output_area highlight-none"><div class="highlight"><pre>
<span></span>20
</pre></div>
</div>
</div>
<p>Negative integers can be used to index relative to the end (right-side)
of the list.</p>
<div class="nbinput docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>In [13]:
</pre></div>
</div>
<div class="input_area highlight-ipython3"><div class="highlight"><pre>
<span></span><span class="n">my_list</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="nboutput nblast docutils container">
<div class="prompt highlight-none"><div class="highlight"><pre>
<span></span>Out[13]:
</pre></div>
</div>