CS 190 Lab 7 - Basics of Git Part 2: Remotes and Github

The purpose of this lab is to become comfortable and fluent with projects using Github. By the end of the lab, you should know how to create repos, add collaborators, clone, push, pull, and fix minor merge conflicts.

For quick reference on the git commands we covered, see the cheat sheet [here] (https://github.com/PurdueCS190/lab7/blob/master/cheat_sheet.md)

The Lab

In this lab, you will work together with a partner to implement a piece of software. Your job is to implement a simple command line interface (CLI) for a four function calculator in Python. The skeleton for this is in calc.py of this repo.

General Setup

This command sets your default editor (just for today's lab) to be pluma for merge messages.

export EDITOR="pluma"

This only lasts as long as the terminal window you ran it within. As soon as you close the window, this setting is lost.

Git Setup

Required since git 2.0, it defines how the pushing mechanism works. This is the most intuitive option.

git config --global push.default simple

Creating, Committing, and Pushing

Choose a partner to start this project off.

Agree on who is partner #1 and partner #2

Do WITH partner on partner #1's computer

1. In your home directory, create a new folder named cs190lab7_<your_username>. Ex. I would create a folder cs190lab7_sopell.

mkdir ~/cs190lab7_$USER

2. You will then cd into the directory created above and initialize a new git repository.

   cd ~/cs190lab7_$USER
   git init

3. Download this template file calc.py into the repository you just created

wget -O ~/cs190lab7_$USER/calc.py https://github.com/purduecs190/lab7/raw/master/calc.py

4. add this file to the repo

git add <filename>

5. Commit this change

git commit -m 'initial commit'

5. Log in to github (upper right hand corner of this page)

6. Create a new repository

7. Enter in a repository name and do not check the box that says initialize with README.

8. Copy the http url from github

8. Add this as a remote and push your commits

git remote add origin <url from github>
git push -u origin master

Notice that these are the exact commands from github! Ask your TA about the -u if you're curious

8. Go to the repository settings

9. Add your partner as a collaborator.

Move to Partner #2's computer

Partner 2 needs a copy of this repo. If you remember from lecture, this is exactly what clone does.

cd ~
git clone <remote url>
cd <repo name>

For the rest of this lab, pay attention to which section you're supposed to do.

Both partners independently

Go back to your own computer and do the steps below.

Run the Script

To run the calculator script, run the command $ python calc.py. The program will prompt you to enter input. Notice that there are 4 functions defined, +, -, * and /

Implement New Operations

By the time you're done, you'll have two new operators, modulus division and exponentiation. One partner will do each.

Note: If you have any questions about Python syntax, ask your TA. It should be very straightforward.

Be sure to test your code to make sure your functions work the way that they should.

1. Open up calc.py in your text editor ($ pluma calc.py &)

Partner 1 only

2. Implement modulus division operator (%)

a) Define a method under the division method that will take two arguments (a and b)and return a modulo b.

b) Add a elif (else if) alongside the others that will check if the operator (op) is equal to the percent sign ("%")

hint: what you're doing is very very similar to the div operator, but instead of using / to do regular division, you can use the % operator to do modulus division.

Partner 2 only

2. Implement the exponent operator (**)

a) Define a method named exp under the division method that will take two arguments (a and b)and return a to the b power. The syntax in python for a to the b is a ** b.

b) Add a elif (else if) alongside the others that will check if the operator (op) is equal to the exponent symbol (**)

hint: what you're doing is very very similar to the multiplication operator, but instead of using *, you can use the ** operator.

Both Independently

3. When you are done with your implementation, commit your changes

Remember git add and git commit. Be sure to check git status and git log afterward to make sure you successfully committed the changes.

4. Do a git pull to check for any changes. Run $ git pull

• If you are the second partner to finish your implementation, you will get a merge conflict. Don't panic. Skip to the next section (merge conflict) and fix it together with your partner.

• If you are the first partner to finish your implementation, move on to step 5.

5. Do a git push to publish your changes to Github so your partner can see them. Run $ git push

When done with this part, wait for your partner to finish his/her implementation.

Merge conflict

Do WITH partner on ONE computer

If you were the second partner to finish your implementation, you will have gotten merge conflict when you tried to pull. This is because you changed the same lines, but did different things (you each implemented different functions)

1. Open up calc.py in your text editor ($ pluma calc.py &)

2. Look for the pattern of <<<<<<<< and >>>>>>>> in the code. This is where the merge conflict exists.

Notice how your changes are marked by HEAD and your partner's changes are marked by a commit hash from the remote.

3. Edit the code to include both functions. Be sure to remove the merge markers (<<<<<<<< and >>>>>>>>), this isn't valid python and shouldn't be left in the file.

4. Scan through the rest of the file to see if there are any other merge conflicts.

5. When you are done editing, git add the file and commit.

6. Run $ git push to publish your changes to Github so your partner can pull them down.

7. Your partner should now run $ git pull on his/her computer to see that you fixed the conflict.

Now both of you should be able to run $ python calc.py on your separate computers and have a fully functioning calculator CLI.

Grading

• Run $ git log -3 and show it to your TA
• Ask any questions that you have

Bonus: Setting up SSH keys

You may have noticed that every time you pull or push to Github, you have to enter your username and password. This is because you are using the HTTPS protocol to connect to Github as a remote. This has a few advantages:

• It's easier and faster to set up
• It will still work on strict firewalls and proxies such as those restricting all ports but port 80

The downside is that you don't want to have to enter your credentials everytime you push and pull. There is another way. You can set up the remote to use SSH instead of HTTPS. SSH uses RSA encryption which you can set up to be passwordless using public keys. There is a great tutorial by Github on how to set up and use this method here. Note that you will need to add an SSH key for every different machine you want to clone on.