Intro to Intermediate Python

Overview#

This lesson starts with a recap of all of the topics covered up to this point, giving you a final chance to express your questions before we move beyond the basics. It then has a very quick overview of the upcoming unit — user input and file I/O, abstraction, modules, and APIs.

Learning Objectives#

After this lesson, you will be able to:

Confidently recap the previous units.
Describe key components of the upcoming unit.

Duration#

20 minutes

Agenda#

Duration	Activity
3 mins	Welcome
8 mins	Basic Topics Recap
4 mins	Intermediate Topics Preview
3 mins	Summary

Talking Points:

This lesson is pretty solidly a review.
Then, we'll very briefly introduce all of the concepts covered the next unit. Don't worry about learning them here! It's the final Python unit and it covers quite a lot, so we'll just give you an overview in advance.

Leveling Up#

You're leveling up! You have the proper foundation. Now, let's check how you're doing.

Let's Review: Lists#

A collection of items stored in a single variable.
Created with square brackets ([]).
Begin counting at 0.

my_queens = ["Cersei", "Daenerys", "Arwen", "Elsa", "Guinevere"]step_counts_this_week = [8744, 5256, 7453, 3097, 4122, 2908, 6720]
# We can also mix types.weird_list = [1, "weird", ["nested list"], "eh?"]

Challenge: Can you recall how to slice a section of the list? For example, items 2 through 5 of step_counts_this_week?

Talking Points:

Lists are a collection of items stored in a single variable.
Lists can be of any type, but they are typically of related items.

Answer: Lists Challenge#

Python uses a : to represent a range of indices.
Beware of off-by-one errors!

step_counts_this_week = [8744, 5256, 7453, 3097, 4122, 2908, 6720]days_2_thru_5 = step_counts_this_week[2:6] # Items 2, 3, 4, and 5

Pro tip: It's 6 instead of 5 because the range is exclusive.

Talking Point:

Many languages have a slice() method, but Python simply uses the colon to represent a range of indices."

Let's Review: Loops and Iteration#

What about looping a list?

my_queens = ["Cersei", "Daenerys", "Arwen", "Elsa", "Guinevere"]
for queen in my_queens:    print(queen, "is the most powerful queen!")

Challenge: What if I want to loop from 1 to 10 and print out the numbers? How do I do this without a data structure to loop over?

Talking Point:

We just reviewed looping over a dictionary. Let's loop over a list.

Answer: Loops Challenge#

To loop 1–10 without a data structure:

# Remember, "i" is a common name for a counter/index in programming!for i in range(1, 11):    print(i)

Why do you think we put 11 in the code?
What values does this print?

Talking Point:

Remember that ranges in Python are exclusive on the end!

Let's Review: Sets#

Lists that don't have duplicates.
Created with curly braces ({}) or from lists with the set() function.
Aren't indexed — elements are in any order!
Handy for storing emails, user names, and other unique elements.

email_set = {"my_email@gmail.com", "second_email@yahoo.com", "third_email@hotmail.com"}# Or from a list:my_list = ["red", "yellow", "green", "red", "green"]my_set = set(my_list)# => {"red",  "yellow", "green"}

Talking Point:

Sets are lists that don't have duplicates.

Let's Review: Tuples#

Lists that can't be changed!
Created with parentheses (()).
Can't add, pop, remove, or otherwise change elements after creation.

rainbow_colors_tuple = ("red", "orange", "yellow", "green", "blue", "indigo", "violet")

Reminder: Tuples are lists that can't be changed.

Let's Review: Dictionaries#

A collection of key-value pairs.
Created with curly braces ({key: value, key: value}).
Values can be anything!

my_puppy = {    "name": "Fido",    "breed": "Corgi",    "age": 3,    "vaccinated": True,    "fave toy": ["chew sticks", "big sticks", "any sticks"]}

Challenge: Can you recall how to iterate (loop) over each key of my_puppy and print out both the key and the corresponding value?

Talking Points:

Dictionaries are made of key-value pairs.
We split lines for readability.

Answer: Dictionaries Challenge#

Iterating a dictionary is similar to a list:

for key in my_puppy:    print(key, "-", my_puppy[key])

Outputs:

name - Fido breed - Corgi age - 3 vaccinated - True fave toy - chew sticks

Talking Point:

Dictionaries are made of key-value pairs.

Let's Review: Functions#

Bits of code that can be used repeatedly.
Enable DRY — Don't Repeat Yourself.
Declared with def, (), and :.
Declare the function above the function call!

# Function definition:def say_hello():    print("hello!")
# Run the function three times.say_hello()say_hello()say_hello()

Let's Review: Function Parameters#

Parameters are in the function definition.

Arguments are in the function call.
Useful for very similar code with only minor variations.

Challenge: Rewrite the code below to use a single function with one parameter.

Talking Point:

Parameters to functions allow us to pass in arguments to use within the function. This is useful when you have very similar code.

Repl.it note: The code here is:

# Function definitions:def say_hello_ada():  print("hello, Ada")
def say_hello_alan():  print("hello, Alan")
def say_hello_linus():  print("hello, Linus")
# Call the functions:say_hello_ada()say_hello_alan()say_hello_linus()

Challenge: Could we do this with a single function that has a parameter called "name"?

Let's Review: Return Statements#

Bring data out of a function.
Cause the function to exit.
Aren't a print statement!

def multiply(x, y):    return x * y
result = multiply(3, 4) # Result is now equal to 12.

Talking Point:

Return statements bring data out of a function. They are not the same thing as print statements, which simply output text.

Let's Review: Classes#

Templates (aka, blueprints) for objects.
Can contain methods and/or variables.
self is a reference to the created object.

class Animal():    def __init__(self):        self.energy = 50
    def get_status(self):        if self.energy < 20:            print("I'm hungry!")        elif self.energy > 100:            print("I'm stuffed!")        else:            print("I'm doing well!")

Challenge: How do you declare a new Animal?

Talking Point:

Classes are essentially blueprints for object-making factories. They can be used to make several objects of the same type.

Answer: Classes

Declaring a new Animal from the class:

my_animal = Animal() # Creates a new Animal instance.my_animal.get_status() # Prints "I'm doing well!"my_animal.energy += 100 # We can access properties!my_animal.get_status() # Prints "I'm stuffed!"

Quick check: How can multiple animals be created?
Show how we can directly access properties.

Let's Review: Inheritance#

A class can inherit properties and methods from another class.

You Do: Create a new class, Dog, which inherits from Animal.

Dog has an extra function, bark(), that prints "bark".
Dog has an extra property, breed.

Talking Point:

Inheritance is all about reusing code. You may have two classes that are related. Inheritance allows you to take advantage of that.

Repl.it note: Here is our Animal() class

class Animal:    def __init__(self):        self.energy = 50
    def get_status(self):        if self.energy < 20:            print("I'm hungry!")        elif self.energy > 100:            print("I'm stuffed!")        else:            print("I'm doing well!")

# Directions Part 1: Create a class, `Dog`.# * `Dog` inherits from `Animal`.# * `Dog` has an extra function, `bark`.# * `Dog` has an extra property, `breed`.
# Directions Part 2: Declare a new dog.# * Call the `bark()` function.# * Give the dog a breed.

Knowledge Check#

We're about to move on to the next unit: Intermediate Python.

Any questions?

Don't be shy! If you have a question, so do others!

Switching Gears: Preview#

The next unit covers many topics, including:

User input
File I/O
Abstraction
Modules and libraries
APIs

You don't need to memorize them now! This is just an overview.

Talking Point:

Here's a preview of what's coming. We'll have lessons on the following topics.

User Input and File I/O#

You've seen this a few times already with input().

We'll build real interactions between your Python programs and other files — or the person using your app!

In this section we'll cover opening, reading, writing, and closing files, as well as browsing directory contents.

Abstraction#

Python has built-in functions for performing common tasks.

You've seen things like my_list.len(), which tells you the length of a list.

But Python has more specialized built-in functions, like chaining lists together:

food = ["pizza", "tacos", "sushi"]colors = ["red", "green"]# => lists_chained =['pizza', 'tacos', 'sushi', 'red', 'green']

This helps you get complex things done more quickly.

We'll learn several of these.

Modules and Libraries#

We mentioned these in the pre-work!

Modules and libraries are:

Code that others have written.
Free to use!
Useful extensions of the Python language (e.g., a fancy date and time formatter).

This one tells us when Mother's Day is for a given year:

Talking Points:

We can use code other people have written. Here, we can get the date of Mother's Day from 2013 with just one line of code!

Repl.it note: This repl.it code has:

from pytime import pytime
# Now we can use any function in the datetime module.
print(pytime.mother(2013))

What Is an API?#

Not only can we use code other people have written; we can also use data that they've made available to us.

We can incorporate stocks, movie ratings, or GIFs from the internet into your program!

This API lists Star Wars characters.

Talking Point:

"API" is a very general term. Usually we actually mean some information from other people.

Repl.it note: This code is:

# Import requests module.import requests
# Call the Star Wars API (swapi).res = requests.get("https://swapi.co/api/people").json()
# Print the result count.print("found", res["count"], "results. Here are the first 10:\n")
# Loop through characters: Append to file and print to screenfor person in res["results"]:    print(person["name"])

Summary and Q&A#

We reviewed topics from earlier lessons:

Lists, sets, tuples, and dictionaries.
Loops and iteration.
Functions, parameters, and return statements.
Classes and inheritance.

We brushed the surface on some upcoming topics:

User input and file I/O.
Abstraction.
Modules and libraries.
APIs.

Let's jump in to it!

Additional Reading and Resources#

Now that you have an understanding of basic programming, here are some cool people to read about:

Ada Lovelace: Regarded as the first programmer.
Alan Turing: Considered the father of theoretical computer and artificial intelligence; helped crack the enigma code during World War II.
Linus Torvalds: Creator of Linux OS and Git.