Intro to Intermediate Python

Learning Objectives

After this lesson, you will be able to:

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

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?

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.

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?

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?

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"}

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")

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?

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

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.

Teaching Tips:

This is long; encourage students to open it in a new window.
Review the answer afterward.

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”?

Function Parameters: Solution

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.

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?

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!"

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.

Teaching Tip:

After a minute, go over the answer:

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.

Inheritance: Answer

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.

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!

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:

Teaching Tip:

This is just a demo slide — run it and mention what it does. Don’t go into modules or syntax, etc.

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 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.

Teaching Tip:

This is just a demo slide — run it and mention what it does. Don’t go into modules or syntax, etc.

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 screen
for 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.