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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Intro to Python ~ Girl Develop It</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="author" content="Girl Develop It">
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<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">
<h3>Intro to Python</h3>
<h4>Class 3</h3>
</section>
<!-- Block 1 25 minutes -->
<section>
<h3>Review</h3>
<ul>
<li>Functions - calls, definitions, returns, arguments</li>
<li>Conditions - if, elif, else</li>
<li>Loops - while, for</li>
</ul>
</section>
<section>
<h3>What we will cover today</h3>
<ul>
<li class="fragment">More Functions</li>
<li class="fragment">Method calls</li>
<li class="fragment">Lists and dictionaries</li>
<li class="fragment">Python builtin functions</li>
</ul>
</section>
<section>
<h3>More with Functions</h3>
<p>Functions can also call other functions.</p>
<p class="fragment">One can use this to break up tasks into small pieces that rely on others to do their work.</p>
<pre><code contenteditable class="fragment python">
from math import sqrt
def absolute_difference(value_a, value_b):
return abs(value_a - value_b)
def find_width_height(x1, y1, x2, y2):
width = absolute_difference(x1, x2)
height = absolute_difference(y1, y2)
return width, height
def get_hypotenuse(a, b):
return sqrt(a ** 2 + b ** 2)
def get_area_rectangle(width, height):
return width * height
def print_area_and_hypotenuse(x1, y1, x2, y2):
width, height = find_width_height(x1, y1, x2, y2)
area = get_area_rectangle(width, height)
hypotenuse = get_hypotenuse(width, height)
print('Area of the rectangle is:')
print(area)
print('The diagonal of the rectangle is:')
print(hypotenuse)
</code></pre>
</section>
<section>
<h3>Function Composition</h3>
<p><strong>Function composition</strong> is when the output of one function acts as the input of another</p>
<pre><code contenteditable class="fragment python">
from math import sqrt
def find_width_height(x1, y1, x2, y2):
return abs(x1 - x2), abs(y1 - y2)
def get_hypotenuse(a, b):
return sqrt(a ** 2 + b ** 2)
def print_hypotenuse(x1, y1, x2, y2):
print('The diagonal of the rectangle is:')
print(get_hypotenuse(find_width_height(x1, y1, x2, y2)))
# f(g(x))
# is the same as:
# y = g(x)
# f(y)
</code></pre>
</section>
<section>
<h3>Method Calls</h3>
<p>Remember: Functions are called by their name - `my_function()` - can be passed data in the form of parameters - `my_function(my_parameter)` and usually return some sort of value. This all happens explicitly.</p>
<p><strong>Methods</strong> meanwhile, are also called by name but they are associated with an object. Really, they are identical to functions except that the data passed into it is passed implicitly.</p>
<p class="fragment">For example, the integers and strings we've been using have methods attached to them</p>
<p class="fragment">We can use the dir() function to see the methods of an object and help() to see what they do.</p>
<pre><code contenteditable class="fragment python">
a = 4
print(dir(a))
name = 'caleb'
sentence = 'the quick brown fox did the thing with the thing'
print(dir(name))
print(name.capitalize())
print(sentence.count('the'))
help(name.upper)
</code></pre>
</section>
<!-- Let's develop it: 5 minutes -->
<section>
<h3>Let's Develop It</h3>
<p>Open a Python shell and define a string varaible</p>
<p>Use 'dir(string_variable)' and the help() function to explore the various methods
<p>Hint: Like functions, some methods take arguments and others don't</p>
<p>Hint: Use help() on a method. It will tell you the arguments to use and the expected behavior</p>
<p>Hint: Don't be afraid of errors. They seem to be in a foreign language but they are there to help you. Read them carefully.</p>
</section>
<!-- Block 2 30 minutes -->
<section>
<h3>Lists</h3>
<p>A list is an ordered collection of elements</p>
<p class="fragment">In Python, a list is defined using `[ ]` with elements separated by commas, as in the following example</p>
<pre><code contenteditable class="fragment python">
words = ['list', 'of', 'strings']
</code></pre>
<p class="fragment">A list can, but doesn't have to be of all one type. A list of one type is <strong>homogenous</strong> as opposed to a list of multiple types, which is <strong>heterogeneous</strong>.</p>
<pre><code contenteditable class="fragment python">
# heterogenous list
words = [0, 'list', 'of', 3, 'strings', 'and', 'numbers']
</code></pre>
</section>
<section>
<h3>List Methods</h3>
<p>Lists have several methods, the most useful of which is `append`</p>
<p class="fragment">A list can be created as an empty list and have values added to it with `append`</p>
<pre><code contenteditable class="fragment python">
to_dos = []
to_dos.append('buy soy milk')
to_dos.append('install git')
print(to_dos)
</code></pre>
<p class="fragment">Therefore, lists are <strong>mutable</strong></p>
<p class="fragment">This means that a list can change values during the duration of a program</p>
</section>
<section>
<h3>Iteration</h3>
<p>Lists and many other collections are <strong>iterable</strong>.</p>
<p class="fragment">Once defined, we can iterate on them, performing an action with each element</p>
<pre><code contenteditable class="fragment python">
shipping_cost = 2.5
prices = [3, 4, 5.25]
costs = []
for price in prices:
costs.append(price + shipping_cost)
for cost in costs:
print(cost)
</code></pre>
</section>
<section>
<h3>Indexing</h3>
<p>An element can also be obtained from a list through <strong>indexing</strong></p>
<p class="fragment">This allows us to obtain an element without iterating through the entire collection if we just want one value.</p>
<p class="fragment">To index on a collection, follow it immediately with `[index]`. (index here is a number, variable or expression)</p>
<pre><code contenteditable class="fragment python">
numbers = [10, 20, 30]
print(numbers[0])
</code></pre>
</section>
<section>
<h3>Indexing continued</h3>
<p class="fragment">Lists and other collections in Python are <strong>zero indexed</strong>. This means that the number 0 refers to first element in the list.</p>
<pre><code contenteditable class="fragment python">
to_dos = [
'install git', 'read email', 'make lunch',
]
print(to_dos[0])
print(to_dos[1])
print(to_dos[-1])
</code></pre>
<p class="fragment">Negative numbers mean "go back from the end this many". e.g. -1 is the last element, -2 is the penultimate</p>
<p class="fragment">An IndexError results if an index exceeds the length of the list minus 1</p>
</section>
<section>
<h3>Dictionaries</h3>
<p>A <strong>dictionary</strong> (sometimes called a "hashmap") is a collection of key/value pairs, defined with '{}'</p>
<pre><code contenteditable class="fragment python">
menu_categories = {
'food': 'stuff you eat',
'beverage': 'stuff you drink',
}
</code></pre>
<p class="fragment">Think of words in a dictionary. The words are keys and the definitions are values.</p>
<p class="fragment">This dictionary would be indexed with strings such as 'food' and 'beverage' instead of integers like in a list</p>
<p class="fragment"></p>
</section>
<section>
<h3>Indexing on Dictionaries</h3>
<p>Dictionaries aren't literally just for definitions. They represent a group of mappings. A mapping might be: menu items -> costs.</p>
<p class="fragment">We can also index on dictionaries.</p>
<p class="fragment">The most common indexes are strings, but they can be whatever type the keys are.</p>
<pre><code contenteditable class="fragment python">
menu = {
'tofu': 4,
}
tofu_cost = menu['tofu']
</code></pre>
<p class="fragment">Indexing on a key that doesn't exist results in a KeyError</p>
<p class="fragment">If you aren't certain a key is present, you can use the 'get' method</p>
</section>
<section>
<h3>Dictionary Methods</h3>
<p>Some of the most essential methods are 'keys', 'values' and 'items'</p>
<pre><code contenteditable class="fragment python">
menu = {
'tofu': 4,
'pizza': 8,
'baguette': 3,
}
print(menu.keys())
print(menu.values())
print(menu.items())
print(menu.get('pizza'))
print(menu.get('water'))
print(menu.get('juice', 5))
</code></pre>
<p class="fragment">'get' will return None if the key isn't present or a default value if provided.</p>
</section>
<section>
<h3>The in operator</h3>
<p>The `in` operator is used to determine if an element is in a given collection</p>
<p class="fragment">For dictionaries, the keys are searched for the element.</p>
<pre><code contenteditable class="fragment python">
color = (255, 255, 0)
if 0 in color:
print('0 is in the color')
menu = {'tofu': 4}
print('tofu' in menu)
names = ['Mary', 'Martha', 'George']
george_present = 'George' in names
</code></pre>
</section>
<!-- Let's develop it: 15 minutes -->
<section>
<h3>Let's Develop It</h3>
<p>Write a program that opens a text file and does some processing.</p>
<ul>
<li>The program should take a word as input and determine if the word appears in the file</li>
<li>The program should use at least one function to do its work and you should be able to import this function in a Python shell and call it with a word and filename</li>
<li>Use the functions from <a href="http://nicklang.com/gdi-intro-python/examples/helpers.py">helpers.py</a> to help with reading in the lines and/or words of the file</li>
<li>Download a book in plain text from <a href="http://www.gutenberg.org/wiki/Main_Page">Project Gutenburg</a> and put it into the same directory as your python file.</li>
</ul>
<p>The next slide has some code and other resources that should help you get started</p>
</section>
<section>
<h3>Let's Develop It- Example Code</h3>
<pre><code contenteditable class="python">
from helpers import generate_cleaned_lines
def is_word_in_file(word, filename):
for line in generate_cleaned_lines(filename):
# line will be a string of each line of the file in order
# Your code goes here.
# Your code should do something with the word and line variables and assign the value to a variable for returning
input_word = raw_input("Enter a word to search for:") # input()
answer = is_word_in_file(input_word, 'pride.txt')
# Display the answer in some meaningful way
</code></pre>
<p>I have used <a href="http://nicklang.com/gdi-intro-python/examples/pride.txt">Pride and Prejudice</a> from Project Gutenburg with my example code. You can click this link and copy/paste the text into a new text file called 'pride.txt' and save it in the same folder as your code</p>
</section>
<!-- Block 3 20 minutes -->
<section>
<h3>Lists of ... Lists</h3>
<p>Lists can contain not only numbers or strings, but also other lists.</p>
<p class="fragment">Such a structure is said to be <strong>nested</strong></p>
<p class="fragment">The following is a list of lists:</p>
<pre><code contenteditable class="fragment python">
game_board = [
['O', 'X', ' '],
[' ', 'X', ' '],
[' ', ' ', ' '],
]
</code></pre>
<p class="fragment">This can be indexed successively with <code>game_board[0][1]</code></p>
</section>
<section>
<h3>Nested Lists continued</h3>
<p>A list can be appended to a list as well</p>
<pre><code contenteditable class="fragment python">
mary_to_dos = ['eat', 'work', 'pick up laundry', 'care for baby', 'sleep']
fran_to_dos = ['eat', 'work', 'call plumber', 'sleep']
baby_to_dos = ['eat', 'sleep']
all_to_dos = []
all_to_dos.append(mary_to_dos)
all_to_dos.append(fran_to_dos)
all_to_dos.append(baby_to_dos)
print(all_to_dos)
for to_dos in all_to_dos:
for to_do in to_dos:
print(to_do)
</code></pre>
<p class="fragment">What if we want to <strong>flatten</strong> the to do's?</p>
<p class="fragment">What if we want the to do's to be unique?</p>
</section>
<section>
<h3>Lists of Dictionaries</h3>
<p>One of the most common and useful nested data structures, is a list of dictionaries</p>
<pre><code contenteditable class="fragment python">
card_a = {
'suit': 'spades',
'number': 4,
}
card_b = {
'suit': 'hearts',
'number': 8,
}
hand = [card_a, card_b]
print('The hand contains:')
for card in hand:
print('A', card['number'], 'of', card['suit'])
</code></pre>
</section>
<section>
<h3>Dictionary of Lists</h3>
<p>A dictionary can also contain values that are themselves other collections, such as lists.</p>
<p class="fragment">Let's revisit the group of to do lists and find a better representation:</p>
<pre><code contenteditable class="fragment python">
mary_to_dos = ['eat', 'work', 'pick up laundry', 'care for baby', 'sleep']
fran_to_dos = ['eat', 'work', 'call plumber', 'sleep']
baby_to_dos = ['eat', 'sleep']
all_to_dos = {
'mary': mary_to_dos,
'fran': fran_to_dos,
'baby': baby_to_dos,
}
for name, to_dos in all_to_dos.items():
print(name, 'needs to: ', to_dos)
# Changing this later can be accomplished with
all_to_dos['baby'].append('cry')
</code></pre>
<p class="fragment">Now the to do lists can be indexed or modified by name</p>
</section>
<section>
<h3>Means of Combination</h3>
<p>Lists, dictionaries, and other collections are all a means of combination.</p>
<p class="fragment">They can be freely combined to create the data structure needed for a particular problem</p>
<p class="fragment">Eg. A list of dictionaries with lists</p>
<pre><code contenteditable class="fragment python">
all_tweets = [
{
'author': 'mary',
'handle': '@hadalittlelamb',
'date': '2013-01-22',
'tweets': [
'at Loco Pops enjoying a Raspberry Sage popsicle',
'Learning Python is so much fun',
],
},
]
</code></pre>
</section>
<section>
<h3>Builtins for collections</h3>
<p>Python provides several functions that help us work with these collections.</p>
<table class="fragment">
<tr>
<td>len()</td>
<td>Given a collection, return its length</td>
</tr>
<tr>
<td>range()</td>
<td>Create a list of integers in the range provided.</td>
</tr>
<tr>
<td>sorted()</td>
<td>Given a collection, returns a sorted copy of that collection</td>
</tr>
<tr>
<td>enumerate()</td>
<td>Returns a list of (index, element) from the list</td>
</tr>
<tr>
<td>zip()</td>
<td>Given one or more iterables, returns a list of tuples with an element from each iterable</td>
</tr>
</table>
</section>
<section>
<h3>Examples of using Builtins</h3>
<pre><code contenteditable class="fragment python">
# Using len() - Determines length
print(len([1, 2]))
# range() - Quickly creates a list of integers
print(range(5))
print(range(5, 10))
print(range(0, 10, 2))
print(range(9, -1, -1))
# sorted() - Sort a given list
grades = [93, 100, 60]
grades = sorted(grades)
print(grades)
</code></pre>
</section>
<section>
<h3>Builtins Examples continued</h3>
<pre><code contenteditable class="fragment python">
# enumerate() - Obtain the index of the element in the loop
print('To Do:')
to_dos = ['work', 'sleep', 'work']
for index, item in enumerate(to_dos):
print('{0}. {1}'.format(index + 1, item))
print(list(enumerate(to_dos)))
# zip()
widths = [10, 15, 20]
heights = [5, 8, 12]
for width, height in zip(widths, heights):
print('Area is {0}'.format(width * height))
</code></pre>
</section>
<!-- Let's develop it: 25 minutes -->
<section>
<h3>Let's Develop It</h3>
<p>Write a program that expands on your previous one. If it is unfinished, feel free to finish the original exercise first. To expand on it, choose one of the following:</p>
<ol>
<li>Determine how many times the user provided word appears in the file and/or what lines it appears on</li>
<li>Change the program so that it counts the number of times each word occurs. E.g. A dictionary of all words in the file, whose values are a count of their occurrences</li>
<li>Use <a href="http://nicklang.com/gdi-intro-python/examples/boilerplate.py">boilerplate.py</a> to help you improve the reusability of the program. (The comments in that file should explain the how and why)</li>
</ol>
<p>Resources for this and the previous exercise are provided on the next slide for convenience</p>
</section>
<section>
<h3>Resources</h3>
<ul>
<li>Helper functions are in <a href="http://nicklang.com/gdi-intro-python/examples/helpers.py">helpers.py</a></li>
<li>Download a book in plain text from <a href="http://www.gutenberg.org/wiki/Main_Page">Project Gutenburg</a> and put it into the same directory as your python file.</li>
<li>You can use this link for <a href="http://nicklang.com/gdi-intro-python/examples/pride.txt">Pride and Prejudice</a>. Click this link and copy/paste the text into a new text file called 'pride.txt' and save it in the same folder as your code</li>
</ul>
<pre><code contenteditable class="python">
from helpers import generate_cleaned_lines
def is_word_in_file(word, filename):
for line in generate_cleaned_lines(filename):
# line will be a string of each line of the file in order
# Your code goes here. Do something with the word and line variables
return result
input_word = raw_input("Enter a word to search for:") # input()
answer = is_word_in_file(input_word, 'pride.txt')
# Display the answer in some meaningful way
</code></pre>
</section>
<section>
<h3>Questions?</h3>
</section>
<section></section>
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// https://github.com/hakimel/reveal.js#configuration
Reveal.initialize({
controls: true,
progress: true,
history: true,
theme: Reveal.getQueryHash().theme, // available themes are in /css/theme
transition: Reveal.getQueryHash().transition || 'default', // default/cube/page/concave/zoom/linear/none
// Optional libraries used to extend on reveal.js
dependencies: [
{ src: 'reveal/lib/js/classList.js', condition: function() { return !document.body.classList; } },
{ src: 'reveal/plugin/markdown/showdown.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
{ src: 'reveal/plugin/markdown/markdown.js', condition: function() { return !!document.querySelector( '[data-markdown]' ); } },
{ src: 'reveal/plugin/highlight/highlight.js', async: true, callback: function() { hljs.initHighlightingOnLoad(); } },
{ src: 'reveal/plugin/zoom-js/zoom.js', async: true, condition: function() { return !!document.body.classList; } },
{ src: 'reveal/plugin/notes/notes.js', async: true, condition: function() { return !!document.body.classList; } }
]
});
</script>
</body>
</html>