Modules and Packages

Lesson Objectives

After this lesson, you will be able to…

Add packages and modules to a Python program.
Create a program utilizing PyTime.
Navigate library documentation.

Discussion: Let’s Dive In

Do you remember itertools?

What do you think these have in common?

itertools.
A Python function that tells us when Mother’s Day is.
A Python function that gets all the contents of a webpage for us.

What is a Module?

Answer: They’re all available to us via modules! (In fact, itertools IS a module).

Modules are collections of useful Python code and functions that we can use.

This is much like a class that someone else has written.
It’s free - less work for us!

Use a function by import <module> at the top of your code, then <module>.function_you_want().

# import < module name > - brings in the module file, so we can use it.
import itertools

food = ['pizza', 'tacos', 'sushi']
colors = ['red', 'green']

# itertools.chain : "Look in the itertools module, and use the chain function"
chained_list = list(itertools.chain(food, colors))

Pro Tip: Check the Additional Reading at the end of the lesson to see how to write your own module!

Python Standard Library

We’re going to look at several different modules to get you used to them.

The Python Standard Library bundles all common modules, so we can just import (use) them.

We’ve seen the itertools module already. Let’s look at another module, random:

import random
# Done! Now we can use any functions in the random module!

# randint is a function in the random module
my_random_number = random.randint(2,8)

# This could be 2, 3, 4, 5, 6, 7, or 8
print(my_random_number)

We Do: Let’s Import Random

Run the code in the repl below. What happened? Why?

Uncomment the first line: import random. Run it again. Try changing the values.

Teaching Tips:

Use this as a teaching aid, not an exercise.
Demonstrate how to import a module.
Point out what happens when we forget the import statement.
Show the correct way to use the basic randint function.
Demonstrate

Talking Points:

Post-activity: “Importing the module tells your program that the module exists - there are thousands of modules, so to save space, your program will only use the ones you tell it to.”
“You may have noticed a NameError. That means it doesn’t know what module you’re referring to since it wasn’t imported.” different values for the randint function as a short “we do” activity. Show a large range and a small range.

Repl.it Note:

# import random
# Done! Now we can use the random module all we want!

# randint is a function in the random module
my_random_number = random.randint(2,8)

# This could be 2, 3, 4, 5, 6, 7, or 8
print(my_random_number)

We do: Exploring the Random Module

How do we know:

What randint does?
What the random module has?

Every module has documentation, which has:

What functions are in the module.
How to use them.

Here is the documentation for the random module.

Can you find our randint function?

Partner Exercise: Random Numbers

Get with a partner and pick a driver! Together:

Find the random function in the documentation. (Yes, a function can have the same name as the module).
Print out a randomly generated number using random().
Run the program several times; is your random number different every time?
Why do you think this is useful?

Protip: The [, in mathematics means inclusive, whereas the ) means exclusive. Thus the possible values include 0.0, but do not include 1.0!

Quick Review

Modules are collections of useful Python code and functions that we can use.

Use a function by import <module> at the top of your code, then <module>.function_you_want().

We’ve looked at two modules: itertools and random.

# Import statements go at the top of your file
import itertools
import random

# Using the randint function in the random module
my_random_number = random.randint(2,8)
print(my_random_number)

# Using the chain function in the intertools module
food = ['pizza', 'tacos', 'sushi']
colors = ['red', 'green']
chained_list = list(itertools.chain(food, colors))

The Python Standard Library bundles all common modules, so we can just import (use) them.

Next up: More random module practice.

We Do: Do You Feel Lucky?

How could you pick a random value from a list? The random module has a function called choice - it works on any non-empty list.

people_in_lottery = ["Tina", "Batu", "Gina", "Jim", "Andres"]
lottery_winner = random.choice(people_in_lottery)
print(lottery_winner, "wins a new car!") # Gina

Let’s try.

Talking Points:

“Let’s switch gears a little bit. Random numbers are nice, but sometimes we have a list and we just want to pick a random item on that list. Suppose we run a lottery. We have a list of everyone who bought a lottery ticket and the winner will get a new car. How can we pick a winner?”

Teaching Tips:

Ask the students to change the names to the people sitting around them. If you have a shy class, this gets people talking.
Try changing the list to hold numbers and other elements.

Repl.it Note:

import random

# Directions
# - Replace the names with your name and 4 nearby classmates.
# - Run the program
# - Who won the car?

# Create a list of candidates
people_in_lottery = []

# This is selecting one winner
lottery_winner = random.choice(people_in_lottery)

# This announces the winner!
print(lottery_winner, "wins a new car!")

Partner Exercise: Let’s Get Random!

Get with a partner and create a local file, random_test.py

Generate a random number with random.randrange(). Print it out.
Create a list, like deck = ["ten", "jack", "queen", "king", "ace"]
Use random.choice() to pick a random card in your deck. Print it out.
Use random.shuffle() to mix up your deck; print that out.

Here is the documentation for the random module, so you can look up functions.

Random Solution

Quick Review

Modules are collections of useful Python code and functions that we can use.

Use a function by import <module> at the top of your code, then <module>.function_you_want().

The Python Standard Library bundles all common modules, so we can just import (use) them. itertools and random are modules inside the Python Standard Library.

# Import statements go at the top of your file - they import straight from the Python Standard Library!
import itertools
import random

# Using the randint function in the random module
my_random_number = random.randint(2,8)
print(my_random_number)

# Using the chain function in the intertools module
food = ['pizza', 'tacos', 'sushi']
colors = ['red', 'green']
chained_list = list(itertools.chain(food, colors))

What is a Package?

A package, also called a library, is a place where one or more related modules are stored.

In technical terms, one or more modules bundled together under a single namespace.
A package is like a folder, while a module is like a file.

The Python Standard Library bundles all common modules - it’s the package with itertools and random modules inside it.

All packages are modules, but not all modules are packages.

Talking Points: - “Both library and package are technically correct and we can use the terms interchangeably.” - “PyTime is an interesting example of a package, because it only has one module in it”

We Do: ModuleNotFoundError

The Python Standard Library has a huge list of modules. But not every Python module in the world is part of it!

pytime is a non-standard module. PyTime can:

Get dates, date ranges, and times.
Find the date of a particular holiday.

Create a new file called pytime_test.py. Put this line in it and run it:

import pytime

What’s happened?

ModuleNotFoundError:

The module isn’t part of the standard library.
If we want to use modules from other packages, we’ll have to tell Python that those packages exist.

Including PyTime

When importing from the standard library, the package is implied:

# (from standard) import MODULE
import random

Otherwise, you need to specify the package!

# from PACKAGE import MODULE
from pytime import pytime

# The names don't need to be the same:
from pygame import joystick
# Yes - that's real!

Change your file to read from pytime import pytime. Does it work?

Protip: Remember that package means library!

Installing PyTime

New packages need to be installed.

Let’s install pytime.

In your command prompt:

pip3 install pytime

Once that’s successful, try again to run your file.

Protip: pip stands for Pip Installs Packages. pip3 uses Python3.

Note: Repl.it is a great website for testing, because it automatically installs libraries for us.

PyTime Holidays

Let’s explore PyTime:

Scan the PyTime docs, to find the mother function.

When is Mother’s Day?

# This gets mother's day of 2016
mothers_day = pytime.mother(2016) # 2016-05-08

What about this year?

# This gets mother's day of this year
mothers_day = pytime.mother()

Try these in your file to be sure you can call PyTime functions!

PyTime Documentation

Here are some examples of PyTime in action:

>>>pytime.father()              # Father's Day without a year (defaults to current year, so this example was generated in 2015)
datetime.date(2015, 6, 21)
>>>
>>>pytime.mother(2016)          # 2016 Mother's Day
datetime.date(2016, 5, 8)
>>>
>>>pytime.easter(1999)          # 1999 Easter
datetime.date(1999, 4, 4)

Quick Review

Not all modules are in the standard library. If you try to import a module Python doesn’t recognize, you’ll get a ModuleNotFoundError.

When importing from the standard library, the package is implied:

# (from standard) import MODULE
import random

Otherwise, you need to specify the package!

# from PACKAGE import MODULE
from pytime import pytime
from pygame import joystick

If you’re using a non-standard package like pytime or pygame, you’ll have to also install it.

You can use the website repl.it for testing small pieces of code - it has packages installed.

Up next: Continuing exploring documentation.

You Do: PyTime Festivals

Look through the PyTime docs; can you find the father and easter functions?

In your local file, pick a year. In that year, print the month and day of:

Mother’s Day.
Father’s Day.
Easter Sunday.

PyTime Festivals: Solution

We Do: The Grinch Who Stole Christmas?

Why does the documentation only have 3 holidays?

Time for some sleuthing! Most times, you only need to look at a module’s documentation. However, sometimes the person that did the documenting didn’t write everything down.

Because a module is simply a .py file, we can view it.

Open up the project’s Github page.
Look at the files and folders near the top of the page.
Click on the folder pytime.
Click on the file pytime.py.
Scroll down to the Festivals section at the bottom of the file.
What function do you see which would likely give you Christmas Day?

You Do: Using the PyTime Module

In your pytime_test.py:

Decide on a list of three holidays you like.

(e.g. Christmas, Halloween…)

Write a function that prompts a user for a year and a holiday.

(e.g. “Enter a year”, then “Choose Christmas, Halloween, or Mother’s Day”)

Have your function print out the date of that holiday for that year.

(e.g. “In 2016, Mother’s Day was on 2016-05-08”)

Summary and Q&A

Modules are .py files with functions. They’re written by other people for us to use!

A packages (a.k.a. library) is a bundle of one or more modules.
Python’s standard library has a lot of common modules! random, itertools, etc.
Nonstandard libraries need to be installed (pip3 install pytime).

To use modules, at the top of your file, put:

# From the standard library: `import MODULE`
import random

# From non-standard packages: `from PACKAGE import MODULE`
from pytime import pytime
from pygame import joystick

# And preface your function with the module name.
mothers_day = pytime.mother(2016) # 2016-05-08

Modules and Packages

Lesson Objectives

Discussion: Let’s Dive In

What is a Module?

Python Standard Library

We Do: Let’s Import Random

We do: Exploring the Random Module

Partner Exercise: Random Numbers

Quick Review

We Do: Do You Feel Lucky?

Partner Exercise: Let’s Get Random!

Random Solution

Quick Review

What is a Package?

We Do: ModuleNotFoundError

Including PyTime

Installing PyTime

PyTime Holidays

PyTime Documentation

Quick Review

You Do: PyTime Festivals

PyTime Festivals: Solution

We Do: The Grinch Who Stole Christmas?

You Do: Using the PyTime Module

Summary and Q&A

Additional Resources