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class2.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Introduction to Python | Girl Develop It Class 2</title>
<meta name="description" content="This is the official Girl Develop It Core Intro to Python course. The course is meant to be taught in four two-hour sessions. Each of the slides and practice files are customizable according to the needs of a given class or audience.">
<meta name="apple-mobile-web-app-capable" content="yes" />
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
<link rel="shortcut icon" href="favicon.ico">
<link rel="stylesheet" href="css/reveal.min.css">
<link rel="stylesheet" href="css/theme/gdiaa.css" id="theme">
<link rel="stylesheet" href="lib/css/light.css">
<link rel="stylesheet" href="css/print/pdf.css" media="print">
<script src="lib/js/head.min.js"></script>
<!--[if lt IE 9]>
<script src="lib/js/html5shiv.js"></script>
<![endif]-->
</head>
<body>
<div class="reveal">
<!-- Any section element inside of this container is displayed as a slide -->
<div class="slides">
<!-- Opening slide -->
<section>
<img src="images/gdi_logo_badge.png" class="img--bare" height="450px" />
<div class="box--small">
<h3><span class="green">Intro to Python Class 2</span></h3>
</div>
</section>
<!-- Block 1 30 minutes -->
<section>
<h3>Review</h3>
<ul class="list--xtall box--small">
<li>Arithmetic and variables</li>
<li>Data types</li>
<li>Text editor, command line, and python shell</li>
</ul>
</section>
<section>
<h3>What we will cover the rest of today</h3>
<ul span class="box--small list--xtall">
<li class ="fragment">Boolean Expressions</li>
<li class ="fragment">Conditionals</li>
<li class ="fragment">Lists</li>
<li class ="fragment">Loops</li>
</ul>
</section>
<!-- BOOLEANS & CONDITIONALS -->
<section>
<h3>Boolean Expressions</h3>
<p class="box copy--small">We can tell the computer to compare values and return True or False. These are called <strong>Boolean expressions</strong></p>
<ul class="list--tall copy--xsmall">
<li class="fragment">Test for equality by using <code>==</code>. We can't use <code>=</code> because that is used for assignment</li>
<li class="fragment">Test for greater than and less than using <code>></code> and <code><</code></li>
</ul>
<pre class="fragment"><code contenteditable class="python" style="min-height: 50px;">
a = 5
b = 5
print a == b
c = 3
print a == c
print c < a
</code></pre>
</section>
<section>
<h3>Boolean Expressions continued</h3>
<p class="box--small copy--small">The following chart shows the various Boolean operators</p>
<table class="copy--xsmall" style="width: auto; margin: 0 auto;">
<tr>
<td style="width: 200px;"><code>a == b</code></td>
<td>a is equal to b</td>
</tr>
<tr>
<td style="width: 200px;"><code>a != b</code></td>
<td>a does not equal b</td>
</tr>
<tr>
<td style="width: 200px;"><code>a < b</code></td>
<td>a is less than b</td>
</tr>
<tr>
<td style="width: 200px;"><code>a > b</code></td>
<td>a is greater than b</td>
</tr>
<tr>
<td style="width: 200px;"><code>a <= b</code></td>
<td>a is less than or equal to b</td>
</tr>
<tr>
<td style="width: 200px;"><code>a >= b</code></td>
<td>a is greater than or equal to b</td>
</tr>
</table>
<pre class=""><code contenteditable class="python" style="min-height: 50px;">
a = 3
b = 4
print a != b
print a <= 3
print a >= 4
</code></pre>
<p class="copy--xsmall">Remember: Equals does not equal "equals equals"</p>
</section>
<section>
<h3>Lists</h3>
<p class="copy--small box--small">A list is an ordered collection of elements</p>
<div class="fragment"><p class="copy--small box--small">In Python, a list is defined using <code>[ ]</code> with elements separated by commas, as in the following example</p>
<pre><code contenteditable class="small python">
words = ['list', 'of', 'strings']
</code></pre>
</div>
<div class="fragment">
<p class="copy--small box--small">A list can, but doesn't have to be of all one type.<br/><small>A list of one type is <strong>homogenous</strong> as opposed to a list of multiple types, which is <strong>heterogeneous</strong>.</small></p>
<pre><code contenteditable class="small python">
words = [0, 'list', 'of', 3, 'strings', 'and', 'numbers']
</code></pre></div>
</section>
<section>
<h3>Appending to list</h3>
<p class="copy--small box--small">Lists have several methods, the most useful of which is <code>append</code></p>
<div class="copy--small box--small">
<p class="copy--small box--small ">A list can be created as an empty list and have values added to it with <code>append</code></p>
<pre><code contenteditable class="small python">
to_do_list = []
to_do_list.append('buy soy milk')
to_do_list.append('learn python')
print to_do_list
</code></pre></div>
<p class="copy--small box--small fragment">Therefore, lists are <strong>mutable</strong></p>
<p class="copy--small box--small fragment">This means that a list can change values<br/>during the duration of a program</p>
</section>
<section>
<h3>Indexing</h3>
<p class="copy--small box--small">An element can also be obtained from a list through <strong>indexing</strong></p>
<p class="copy--small box--small fragment">This allows us to obtain an element if we just want one specific value.</p>
<div class="fragment"><p class="copy--small box--small">To index on a list, follow it immediately with <code>[index]</code>.</p>
<pre><code contenteditable class="small python">
numbers = [10, 20, 30]
print numbers[0]
</code></pre></div>
<p class="copy--small box--small fragment">Lists (and other data types) start at the number 0 and count up.</p>
</section>
<section>
<h3>Length and More Indexing</h3>
<p class="box--small copy--small">You can get the length of a list with <strong>len(list)</strong></p>
<p class="box--smail copy--small">You can also use the length of the list to index the last element.</p>
<pre><code contenteditable class="small python">
to_do_list = [
'learn python', 'read email', 'make lunch',
]
print len(to_do_list)
print to_do_list[0]
print to_do_list[2]
print to_do_list[len(to_do_list)]
print to_do_list[len(to_do_list) - 1]
</code></pre>
<p class="box--small copy--xsmall fragment">An IndexError results if an index exceeds the length of the list minus 1</p>
</section>
<section>
<h3>Let's Develop It</h3>
<p class="copy--small box--small">Take the list below and try to do the following:</p>
<p class="copy--small box--small">Append to the list a chore you have to do</p>
<p class="copy--small box--small">Use indexing to find the first and third chores on the list</p>
<p class="copy--small box--small">Find the length of the list</p>
<p class="copy--small box--small">Use indexing to find the last chore in the list</p>
<pre><code contenteditable class="small python">
['Make the bed', 'Cook dinner', 'Feed the dog', 'Buy groceries']
</code></pre>
</section>
<section>
<h3>Conditionals</h3>
<p class="copy--small box--small">When we want different code to execute dependending on certain criteria, we use a <strong>conditional</strong></p>
<div class="fragment box--small">
<p class="copy--xsmall">We achieve this using <strong>if</strong> statements</p>
<pre><code contenteditable class="small python">
if x == 5:
print 'x is equal to 5'
</code></pre></div>
</section>
<section>
<h3>Conditionals</h3>
<div class="fragment box--small">
<p class="copy--xsmall">We often want a different block to execute if the statement is false.<br/>This can be accomplished using <strong>else</strong></p>
<pre><code contenteditable class="small python">
if x == 5:
print 'x is equal to 5'
else:
print 'x is not equal to 5'
</code></pre>
</div>
</section>
<section>
<h3>Indentation</h3>
<p class="copy--small box--small">In Python, <strong>blocks</strong> <span class="green">begin when text is indented</span> and<br/><span class="red">ends when it returns to the previous indentation</span></p>
<p class="copy--small box--small fragment">Indentation is <strong>very</strong> sensitive in python. Let's write a python file that practices indentation and conditionals</p>
<div class="fragment">
<p class="copy--small box--small">Write this into your text editor and save the file as class2.py in your gdi-intro-python folder.
<pre><code contenteditable class=" python">
print "It's your birthday!"
answer = raw_input("How old are you? ")
age = int(answer)
if answer < 21:
print "You may not have a beer, but here's some juice!"
else:
print "Here's some beer!"
print "Happy birthday!"
</code></pre></div>
</section>
<section>
<h3>Chained conditionals</h3>
<p class="box--small copy--small">Conditionals can also be <strong>chained</strong></p>
<div class="fragment"><p class="box--small copy--small ">Chained conditionals use <code>elif</code> as an additonal check after the preceeding <code>if</code> predicate was False. For example:</p>
<pre><code contenteditable class=" python small">
if x < 0:
print "x is negative"
elif x > 0:
print "x is positive"
else:
print "x is 0"
</code></pre></div>
</section>
<section>
<h3>Nested conditionals</h3>
<p class="box--small copy--small">Conditionals can also be <strong>nested</strong></p>
<p class="box--small copy--small fragment">Nested conditionals occur inside of other conditionals, and are indented over once more. When the code block is complete you move back.</p>
<div class="fragment"><p class="box--small copy--small">Edit your python file to contain the following:</p>
<pre><code contenteditable class="small python">
print "It's your birthday!"
answer = raw_input("How old are you? ")
age = int(answer)
if answer < 21:
print "You may not have a beer, but here's some juice!"
else:
beers = raw_input("How many beers do you want?")
beers = int(beers)
if beers > 3:
print "Oops, you're drunk!"
elif beers > 1:
print "You got a little tipsy"
else:
print "Looks like you're the designated driver"
print "Happy birthday!"
</code></pre></div>
</section>
<!-- Let's develop it: 10 minutes -->
<section>
<h3>Let's Develop It</h3>
<p class="box--small copy--small">Write a program that uses if statements to determine<br/>what to do given some user input</p>
<p class="box--small copy--small">The code below is an example:</p>
<pre><code contenteditable class=" python">
health = 100
print "A vicious warg is chasing you."
print "Options:"
print "1 - Hide in the cave."
print "2 - Climb a tree."
input_value = raw_input("Enter choice:")
if input_value == '1':
print 'You hide in a cave.'
print 'The warg finds you and injures your leg with its claws'
health = health - 10
elif input_value == '2':
print 'You climb a tree.'
print 'The warg eventually looses interest and wanders off'
else:
print 'Invalid option.'
</code></pre>
</section>
<!-- LOOPS -->
<!-- Block 2 25 minutes -->
<section>
<h3>Iteration</h3>
<p class="box--small copy--small">It is often useful to perform a task and to repeat the process until a certain point is reached.</p>
<p class="box--small copy--small fragment">The repeated execution of a set of statements is called <strong>iteration</strong></p>
<div class="fragment"><p class="box--small copy--small">One way to acheive this, is with the <strong>while</strong> loop.</p>
<pre><code contenteditable class=" small python">
user_input = raw_input('would you like to quit? (y/n) ')
while user_input != 'y':
user_input = raw_input('would you like to quit? (y/n) ')
print 'quitters never win!'
</code></pre></div>
<p class="box--small copy--small fragment">As long as the while statement evaluates to True, the code block beneath it is repeated.</p>
</section>
<section>
<h3>While loops</h3>
<p class="box--small copy--small">Consider the following example that uses iteration with a while loop</p>
<div class="fragment"><pre><code contenteditable class="small python">
input_value = raw_input('Enter a positive integer:')
user_number = int(input_value)
while user_number > 0:
print "The user's number is still positive, let's subtract 1"
user_number = user_number - 1
print "User's number is no longer positive."
</code></pre></div>
<p class="copy--small box--small fragment">This implementation does not work for negative numbers. Why?</p>
</section>
<section>
<h3>For loops</h3>
<p class="copy--small box--small">It is also useful to loop through a collection of elements, visiting each one to do some work, then stopping once all elements are processed.</p>
<p class="copy--small box--small fragment">This can be accomplished with a <strong>for</strong> loop</p>
<div class="fragment"><p class="copy--small box--small ">First, we need a collection. We create a <strong>list</strong> of numbers to loop over. This is called <code>numbers</code> in the following example</p>
<pre><code contenteditable class="small python">
shipping_cost = 2.5
prices = [3, 4, 5.25]
costs = []
for price in prices:
costs.append(price + shipping_cost)
print costs
</code></pre></div>
</section>
<section>
<h3>Range</h3>
<p class="fragment box--small copy--small">What do you think the following functions output?</p>
<pre><code contenteditable class="small fragment python">
range(5)
</code></pre>
<pre><code contenteditable class="small fragment python">
range(5, 10)
</code></pre>
<pre><code contenteditable class="small fragment python">
range(10, 20, 2)
</code></pre>
<pre><code contenteditable class="small fragment python">
range(20, 8, -2)
</code></pre>
</section>
<section>
<h3>For loops continued</h3>
<p class="copy--small box--small">Let's examine the example carefully</p>
<pre><code contenteditable class="small python">
for number in range(5):
print "The current number is:"
print number
</code></pre>
<p class="fragment copy--small box--small">This for loop has three parts:</p>
<ul class="list--tall copy--xsmall">
<li class="fragment">The collection to loop over - range(5)</li>
<li class="fragment">The name WE give each element when the loop begins again - number</li>
<li class="fragment">The block of statements to execute with the element - The two print statements</li>
</ul>
</section>
<section>
<h3>Variable name in for loops</h3>
<p class="copy--small box--small">In our last example, we named our variable "number".</p>
<p class="copy--small box--small fragment">We could have chosen any word, and the computer would process the code.</p>
<div class="fragment"><p class="copy--small box--small">This is a great example of the computer
<em>processing,</em> not <em>understanding.</em></p>
<pre><code contenteditable class="small python">
for moose in range(5):
print "The current number is:"
print moose
</code></pre></div>
</section>
<!-- Let's Develop It - 10 minutes -->
<section>
<h3>Let's Develop It</h3>
<p class="copy--small box--small">Let's iterate through the following list:</p>
<p class="copy--small box--small"><pre>["Mary", "had", "a", "little", "lamb"]</pre></p>
<p class="copy--small box--small fragment">For each word, check if the letter "a" is in the list.</p>
<div class="fragment"><p class="copy--small small--box">For example:</p>
<pre><code contenditable class="small python">
The word Mary contains the letter a.
The word little does not contain the letter a.
</code></pre></div>
<p class="copy--small box--small fragment">"What about the letter "m"?</p>
</section>
<!-- OUTRO -->
<section>
<h3>Questions?</h3>
</section>
<section>
<h3>Exercise</h3>
<p>Write a script that asks the user to guess a number between 1 and 100</p>
<ul>
<li class="future"><p>If their guess is within 20, tell them they are 'warm'</p></li>
<li class="future"><p>If their guess is within 10, tell them they are 'hot'</p></li>
<li class="future"><p>If their guess is within 5, tell them they are 'scalding'</p></li>
<li class="future"><p>if their guess is within 50, tell them they are 'cool'</p></li>
<li class="future"><p>otherwise tell them they are 'cold'</p></li>
<li class="future"><p>If they guess the number, congratulate them and ask if they'd like to play again.</p></li>
</ul>
<h6>Optional Extra Challenge: Let them know if they are 'warmer' or 'colder' than their last guess.</h6>
</section>
<section>
<h3>Optional Boolean Practice</h3>
<p>Do this excercise from Learn Python The Hard Way</p>
<i>Make sure to do these problems by hand, not with python! </i>
<h6><a
href="http://learnpythonthehardway.org/book/ex28.html">http://learnpythonthehardway.org/book/ex28.html</a></h6>
</section>
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