Git is a tool to manage sourcecode

Never lose your coding progress again

Windows

Go to your programs overview and start Git Bash

Everywhere else

Open a terminal window

cd into the directory where you save your python projects

Type mkdir test to create a new empty folder called test

Type cd test to go to the new folder

Open your text editor and create the files README.md and test.py with some dummy content like hello world or test

Save the files to the folder you created on the previous slide

Type ls in the terminal to verify that you saved the files correctly

The folder in which you saved the files is called the

working directory

we now want to manage this directory using git

To make the current directory a git repository type git init on the terminal

git init creates a hidden .git folder in the working directory to store all its data

Type ls -a to see the hidden .git directory

Type ls .git to see the content of the .git directory

We want git to keep track of our README.md and test.py files

Git does not perform any automatic synchronizations in the background like e.g. Dropbox does

Instead we have to manually inform git about changes we made to the files in the working directory

$ git status
On branch master

Initial commit

Untracked files:
  (use "git add <file>..." to include in what will be committed)

  README.md
  test.py

nothing added to commit but untracked files present (use "git add" to track)

Use the git status command to find the files in the working directory that git does not yet track

On the previous slide git told us to use git add to start tracking README.md and test.py

Type git add README.md test.py on the terminal

git add creates copies of the files and saves them under the .git directory

It also calculates hash values that uniquely identify the contents of the files

$ git status
On branch master

Initial commit

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)

    new file:   README.md
    new file:   test.py

If we now rerun git status it will tell us, that README.md and test.py are "to be committed"

A commit in git is a snapshot of the whole project at a given time

As long as you do not actively break your git repository you can always go back to every previous commit in your git history

E.g. when you accidentially delete one of your source-files you will only lose the work you did since the last commit

Or when your project stops working you can always go back to a previous version that is known to work and find the breaking change

In order to create a new commit you:

• git add every file that you want to be part of the commit
• use git status to check if you included all your changes
• Type git commit -m "Your description here"

You should replace "Your description here" by a description of the changes you did since the last commit

In the example we are now about to commit the changes to README.md and test.py

Type git commit -m "My 1st commit" as this is our first commit in this repository

You can now use git log to see the history of this repository

For the next commit we want test.py to output "Hello World!" when it is executed

Replace the text you put into text.py with the following program:

1 print('Hello World!')

Create a commit that includes the new test.py

Make sure to give it a good description of the changes

The second commit stores:

• A reference to the previous commit
• A description "Better test.py"
• References to the old README.md and the new test.py

Use git log to look at the history of the project

Although not losing any local work is already a great feature git can do even more

One of the other mayor features is being able to synchronize repositories with a server

This allows you to simultaneously collaborate on software over the internet

Sign into/create an account on a codesharing site that supports git like Gitlab, Bitbucket or Github

In order to use a git-based codesharing site you have to generate a ssh public key once and configure the site to associate it with your account

Click here for a tutorial on how to generate a public key

After configuring your public key you can create a new project …

… copy the address of the new project …

… and add it to your git repository as a remote using the command:

git remote add origin [address of the project]

Once again git does not perform any automatic synchronizations.

In order to publish your changes to the server you have to use the git push command

To setup this remote as a default type git push --set-upstream origin master to push your changes to the server

In order to collaborate on a project you have to add another user as a developer to the project

Add a partner to your project

To get a copy of an already existing repository you can use the git clone command

Ask your partner for the address she/he used in the git remote add [address] command

Type cd .. to go one directory up

Type git clone [address] partner to get a copy of your partners code into a new partner folder

Git has a lot more feature than we covered here

We have not covered:

• What to do if you and your partner made changes to the code at the same time
• How to retrieve old commits
• What branches are
• Merging, rebasing, stashing

But as long as you stick to the commands that were demonstrated in this turorial you will not lose progress because of accidentially overwritten/deleted files

• git init - Initialize a repository in the current directory
• git remote add - Tell git that you want to use a server
• git clone - Clone a remote repository
• git status - Run this command whenever you need advise
• git add - Tell git about the newest version of a file
• git commit - Create a snapshot of the current state and give it a name
• git pull - Get the latest commits from a server
• git push - Send the latest commits to a server

$ git push
To remote
 ! [rejected]        master -> master (fetch first)
error: failed to push some refs to 'remote'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

Problem: git push gets rejected when there are changes on the server you do not have locally

Workaround: git pull the changes first

$ git pull
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From remote
   bcdbca8..0a78d9b  master     -> origin/master
Updating bcdbca8..0a78d9b
error: Your local changes to the following files would be overwritten by merge:
    README.md
Please commit your changes or stash them before you merge.
Aborting

Problem: git pull complains about uncommited files

Workaround: git add and git commit your local changes and git pull again

$ git pull
Auto-merging README.md
CONFLICT (content): Merge conflict in README.md
Automatic merge failed; fix conflicts and then commit the result.

Problem: git pull complains because you and someone else edited the same file

Workaround: Go through every file git complains about, search for any occurence of <<<<<<< and decide which version you want to keep. git add and git commit the new version.

Problem: Everything is broken, nothing works, my computer is on fire

Workaround: Clone the repository from the server, forget about your old repository and get a fire extinguisher