Codelab 1: Python 101

Changelog

September 7th, 2017

Updated future codelab due dates

September 3rd, 2017

Added grading section.
Emphasized vagrant destroy section.
Silenced the curl command in Vagrantfile.
Added submission instructions.
Released Codelab 1 🎉.

Due Date

This codelab is due on Sunday, September 10th at 11:59:59PM. Future codelabs will be due at midnight a week after release (usually the following Friday).

Goal

In this codelab, you'll learn (or review!) the basics of Python. We will be using Python throughout this class to build projects with AWS. Starting with next week's codelab, we will also be using the boto3 library, which is the official AWS SDK for Python.

Getting Started

Vagrant

We will be using Vagrant, a tool for managing virtual machines via a CLI, in this class in order to create lightweight, reproducible, and portable development environments.

Installation

To get started, you will need to install Virtualbox and Vagrant. If you are on Mac, you can do the installation with brew (see below). Otherwise, install Virtualbox from here and Vagrant from here.

Verify that the installation succeeded:

$ vagrant version
Installed Version: 1.9.8
Latest Version: 1.9.8

You're running an up-to-date version of Vagrant!
$ virtualbox --help
Oracle VM VirtualBox Manager 5.1.26
(C) 2005-2017 Oracle Corporation
All rights reserved.
...

Now, let's test that you can successfully create a virtual machine (also called a "box") with Vagrant. Create a Vagrant box and launch it:

$ vagrant init ubuntu/trusty64
$ vagrant up
$ vagrant ssh

The init step will auto-generate a Vagrantfile for you. This file specifies all of the configuration for your virtual machine. If you look at it now, you will see that it only specifies which type of virtual machine to install. In this case, we are creating a virtual machine that is running 64-bit Ubuntu Linux 14.04 (also known as "trusty").

If you've gotten this far, then everything works. Go ahead and shut down this virtual machine by running the following command:

$ vagrant halt

Destroying Vagrant Boxes

Even though your VM has been halted, it is still stored on your computer. Since you will be creating a new Vagrant box for each codelab, you will want to make sure to completely destroy each VM. To do so, run the following command:

$ vagrant destroy

macOS

First, install brew if you do not already have it on your system:

$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Now, use brew cask to install Virtualbox and Vagrant:

$ brew cask install virtualbox
$ brew cask install vagrant

Continue with the installation instructions from above, starting at the installation verification.

Codelab Vagrant Environment

For this codelab, I will be providing you with a Vagrantfile that specifies all of the configuration.

First, clone the class repository onto your system:

$ git clone https://github.com/UMD-CS-STICs/389Lfall17.git

Each week, when new content is pushed into this repository, you'll need to pull in these changes. All you need to do is run:

$ git pull

This is a good time to remind you to not share any of your solutions to these codelabs or projects. However, when you start on the final project, you are welcome to share that on GitHub or elsewhere.

Learn Python in Y Minutes

Since you are already familiar with Ruby from CMSC330, then you mostly just need to learn the syntactical differences. For that, I ask that you go through the "Learn X in Y Minutes" tutorial for Python 3 here:

https://learnxinyminutes.com/docs/python3/

More on Python (Optional)

If you would like to take a deeper dive into the internals of Python, I would recommend checking out the following resources (read: skimming the parts that interest you!):

Python Library Reference Python Language Reference

Assignment

To give your new Python knowledge a test drive, you're going to write a few simple functions.

Open the folder lectures/lecture-01/codelab/. Go ahead and open functions.py and test.py in your editor. functions.py contains the three functions that you will need to implement, and test.py contains the public tests that you should pass in order to get full credit.

foobar_flip(value)
string_compress(string)
fibonacci(n)

Note that to pass the the final public test (test_large_numbers), you will need to write your fibonacci method using a Python dictionary. If you don't solve this function, you'll still get full credit.

To run this codelab, you will need to launch the Vagrant environment. It comes pre-configured with our Python environment.

$ # /lectures/lecture-01/codelab
$ vagrant up
$ vagrant ssh
vagrant$ cd code

Now run the tests:

vagrant$ python tests.py

Now implement the functions. You can implement them one at a time, as all of the test cases will execute independently.

You'll see a message like this when you've passed all of them:

$ python test.py
........
----------------------------------------------------------------------
Ran 8 tests in 0.002s

OK

When you are finished, make sure to run vagrant destroy. Note that this will not remove any source code from the shared code folder.

Grading

For this codelab, you will get full credit if you complete at least the required public tests (so all of them, except test_large_numbers).

If some codepath is not tested, such as the behavior of foobar_flip when a value is provided that is not "foo" or "bar", then you are free to handle it however you would like. Pick something reasonable, like raising a ValueError.

Submission

To submit this codelab, zip the codelab folder under lecture-01 and upload it to the submit server.

Codelab 1