Version control with git

Outline

Topics:

Version control
Using git
Github

Git

Version control system
Useful for collaborating on large codebases
Originally for Linux code (30 million lines)
Created by Linus Torvalds
Rant

Github

Provides a remote git server for free
Has a web front-end for navigating the code
Makes it easy to fork and open pull requests
More on this later...

Example - CPython

The code for Python itself is kept under version control using git and hosted on github:

https://github.com/python/cpython

Start a git project

Create repo on Github
Clone the repo

$ git clone https://github.com/myname/myrepo.git
$ cd myrepo
$ git status

Change the code

$ git status       # Check all clean
$ gedit README.md  # Make changes and save
$ git status       # Shows changed files
$ git diff         # Shows the changes

diff --git a/t.py b/t.py
index c5d61cf..fbcc63c 100644
--- a/t.py
+++ b/t.py
@@ -1,7 +1,7 @@
 def myfunction(x):
     y = 2
     z = 3
-    return y + z - x
+    return [y + z - x]

 # here is some code

Commit the changes

$ git status
$ git diff
$ git add README.md   # Tell git you want to commit
$ git commit -m "Add installation instructions in README"

Commit history

Commits represent the history of your work

initial commit -- A -- B -- C -- HEAD

Use git log to see the history (or look on github)

Committing

Always check (status/diff) before committing.
Git saves the commit as a "version" of your code.
Can make more changes and commits after
Use good commit messages

Push/pull

Git stores commits in the .git folder.
Use push to send them to github

$ git status   # Always check clean first
$ git log      # What am I pushing?
$ git push

Get changes from github:

$ git pull

Push/pull

Send commits to and from github

push/pull
                               push
                           ----------->
          your computer                    github
                           <-----------
                               pull

Git

Stores every commit forever
Use git log to see commits
Can switch to old commits (git checkout ab1234)
Use git checkout master to get to latest commit