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Laboratory 1 Introduction to the Python/git workflow

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Computer Science CS134
Laboratory 1
Introduction to the Python/git workflow

Objective. To become comfortable working with Python and git.
This week we will spend a little time on some little programs. These programs will give you a
taste of what it is like to work with Python. Beneath most modern operating systems is a Unixbased, extensible operating system. We’ll be using git to check out and turn in our work. We’ll
think about what makes an editor suitable for programming. Finally, we’ll get our  rst exposure
to python3, the primary tool of this semester’s study. Your job, this week, is to begin developing
a working knowledge of these systems. It will be worth it.
Setting up your environment. Before we begin our  rst lab exercise, it is important that we
make sure that we have all the utilities we need. We assume that you have completed all of the
con guration described in the handout Setting Up Your Computer. You can  nd this handout
on the course website, http://www.cs.williams.edu/~cs134.
When you are working from o -campus (all of us will, at some point this semester), you will
need access to the Williams VPN, by installing Cisco’s AnyConnect software. See OIT’s Software
page http://oit.williams.edu/software for installation instructions.
Establishing your identity. We have sent you your Computer Science credentials: a username
and password that allows you to access our facilities. Please, make sure you change your password.
Those credentials identify who you are, with our servers. We also sent you a two digit code that
will be your anonymous identi er throughout the semester. At times, we may ask you for your two
digit id to identify who you are, with our graders.
We also need to help your machine identify who you are, as well. Before you turn in your  rst
assignment, we must make sure you have established your git identity. If you have not already
done this during setup, carefully type the following commands into the shell, replacing Joe Cool’s
identity with your own:
git config –global user.name ‘Joe Cool’
git config –global user.email ‘jc8@williams.edu’
git config –global push.default simple
git config –global core.editor nano
Your identity is used to digitally sign your submitted work.
Organizing your work. Unix directories correspond to folders in your Mac or Windows operating system. You will be creating many  les on your computer for this class. We suggest that you
put all of your work in a single folder, called cs134, located in your home directory. From within
the Terminal window (on Macs) or the Ubuntu app window (on Windows)1
, do the following:
1From this point on, when we refer to the Terminal, we’re referring to either the Terminal app window on Macs,
or the Ubuntu app window on Windows machines.
1. Create your cs134 directory:
mkdir cs134
2. Now, descend into the cs134 directory:
cd cs134
3. At this point, we’re going to establish secure connections with our git server, evolene:
curl http://www.cs.williams.edu/~cs134/evolene.pem -o ~/cs134/evolene.pem
git config –global http.sslCAInfo ~/cs134/evolene.pem
This downloads the certi cate for evolene and ensures that git uses it whenever we exchange
information with the server. Do not change or move the  le evolene.pem, or you will  nd
you will no longer be able to connect to the server. Again: this only needs to be done once
this semester.
4. If you are o  campus, start the VPN server. (It should connect to ssl-vpn.williams.edu.)
5. Now that we’re set-up, we’re going to retrieve the  les we need to complete this week’s lab.
This will create a new directory in your cs134 folder with the name lab01 containing your
lab work. Type
git clone https://evolene.cs.williams.edu/cs134-labs/22xyz3/lab01.git lab01
Here, evolene.cs.williams.edu is the full name of the git server dedicated to holding all
of our collective work. The cs134-labs reference is the CS134 lab directory on that server
(many courses make use of evolene), and lab01.git is the name of the repository. The
identi er 22xyz3 should be replaced with your CS identity. It is the folder that contains all
of your repositories on the server. You will be asked for your CS credentials.
If you’ve made it this far, congratulations! Now, you’re ready to begin work.
This week’s lab. This week we’ll get introduced to the weekly work ow associated with the
course.
1. You can now change your directory to be the starter subdirectory of cs134 with:
cd ~/cs134/lab01
Whenever you begin a session of work, you should make sure you get the latest copy of your
work. This is called pulling the repository from the server. You should
git pull
Since we just cloned the repository, it’s unlikely that anything is out-of-date. Still, we always
perform this simple check.
First, we’ll edit the hello.py  le, adding the following Python commands:
# My first python program!
print(‘Hello, world!’)
Save the  le. Now, at your prompt (represented by the $, here) run the Python script in the
shell:
$ python3 hello.py
Hello, world!
Congratulations, you’re a programmer! We’ll tell git that we changed the  le:
git add hello.py
git commit -m “I’m a programmer!”
The commit command will only store the changes of  les you’ve add-ed.
We can send these committed changed back up to evolene:
git push
You’ll be asked for your CS password. From now on, any time you pull the lab01 repository,
the hello.py  le will re ect the changes you just made.
Sometimes we’ll create new  les we want to turn in for credit. Suppose we create a  le called
goodbye.py. We should add the  le and commit changes to our repository:
git add goodbye.py
git commit -m ‘Another great program!’
You should commit every time you think you’ve made progress. Committing is an important
part of managing the progress you make. It is also helpful for backing up your work.
Whenever you’re  nished with a work session, you should always commit one last time and
push the changes to the server:
git commit -am ‘Done with work today!’
git push
The -a switch causes any  le that has ever been add-ed to be committed. This guarantees
you get the latest version of your work every time you pull.
2. Use your editor to write a paragraph about yourself in a  le called AboutMe.txt. Who are
you? What do you enjoy doing? Where are you from? Where can you get good food in your
hometown? Add and commit this work:
git add AboutMe.txt
git commit -m ‘Added restaurant recommendation.’
3. The GradeSheet.txt  le describes the expectations we have for each lab, and is where you
can  nd our comments after we grade your work. You might  nd it useful to look at this
le before you turn in you work to make sure you have not missed an important part of the
assignment.
4. Every week you will need to certify that your work is your own. Edit honorcode.txt and,
if appropriate, write your name below the Honor Code statement. If you received help from
other students in the course, you must indicate who that was, as well. Now, commit that
work:
git add honorcode.txt
git commit -m ‘Signed the honor code.’
5. Final Task. Now, push your work up to the server, to be graded, by Thursday at 5pm.
git push
Make sure that you always push your work up to the server. If you don’t do this, we cannot
grade your work!
What to expect. Your work is due on Thursday, at 5pm. Over the course of the next few days,
we provide feedback and grade your work. After we have graded your work, you can use
git pull
to download our comments, found in the GradeSheet.txt  le.
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