2/9 Research Software Engineering with Python (COMP0233) - Git Part 2

Branching and merging.

What is it and why does it matter? In short, with branching you can maintain and work on separate versions of your code independently.

And merging is kind of the inverse operation where you bring changes of your files from one branch to another.

Well, that all sounds very airy-fairy and very general and may not make a lot of sense initially.

So let's do an example.

Let's say you have a Python script that analyzes some data.

It's a crucial piece of your research work.

You spend a long time developing it and you have to use it regularly to get results for your project.

But at the same time, there are also some features you want to add.

But, on the other hand, you really need this script to work and you can't afford to break it, so what do you do? And this is exactly where Git branches come to the rescue.

To begin with, Git always comes with a single branch by default.

It's usually called main or master.

This main or master branch is like the trunk of a tree from which you can create as many branches as you like.

So let's do that.

The git command for this is git branch followed by the name of the new branch and for this example we choose the name development.

so for this command it would be git branch development and voila you have a new branch called development and from now on git maintains two versions of your script and you can use one unchanged to run your analysis on the main branch and add some new features to the script on the development branch To switch between branches you would use the command git checkout followed by the name of the branch you want to switch to.

So you do git checkout main if you want to run the stable python script and you do git checkout development if you want to make changes.

If at any time you're unclear which branch you're on you can simply type in git status And it will tell you.

Well, so far so good.

But at some stage, you work on the development branches done.

You're happy with the changes and you want to run the change script from now on.

There's no need to keep separate branches anymore.

And in short, what you want to do is to merge your changes from the development branch back into the script on the main branch.

The git command for this is called git update.

merge followed by the name of the branch from where you want to bring changes in and this means that if you do a merge you need to be on the right branch this can create some confusion and i myself fall victim of merging changes into the wrong branch in the past so before you do a git merge make sure you're on the right one with git status So back to the example from earlier.