Workshop 4 - Using Conditions and Writing Functions

Workshop goal

To learn to use logic and modularity to make code flexible and reusable.

Episodes and questions

4.1 Making Decisions with Conditional Statements

• How can my programs do different things based on data values?

4.2 Creating Functions

• How can I define new functions?
• What’s the difference between defining and calling a function?
• What happens when I call a function?
• How do I work with variables inside and outside of functions?
• How do I make sure my functions are doing what I want?
• How do I use docstrings to make my functions more usable?

Setup

These instructions assume you’ve already installed the required software for this workshop series (instructions in Introduction and Setup).

If you have not finished the installation requirements, you can write code here: https://mybinder.org/v2/gh/koudyk/blank-python-notebook/HEAD?urlpath=%2Fdoc%2Ftree%2Findex.ipynb

1. Create a project folder where you’ll store data and Python scripts, or find the folder you used in previous workshops in this series.
2. Download this file, put it in your folder, and extract the files in it (you should end up with 9 new csv files in your folder).
3. To open your project in VS Code, open VS code, select File > Open Folder, and open the folder with the data.

Create a local Python environment, if you haven’t in a previous workshop

Skip this step if you created a Python environment for the previous workshop.

Best practice in Python is to create a virtual environment for each project, which contains all the specific libraries (and specific versions) that you need for that project.

We will use the venv tool to create an environment with the following steps:

1. Open the Command Palette with Ctrl+Shift+P
2. Type in Python: Create Environment and click on it
3. Select venv as the tool we want to use to create the environment
4. Select the Python interpreter that you want to use (probably the one with the highest numbers, starting with something like Python 3.10)

After following these steps, VS Code will create a .venv folder in your project folder.

Activate the environment

VS Code may give you a pop-up asking if you want to activate the virtual environment that you just created. If it does, select Yes.

If not, you can run a command in the terminal (in VS Code) to activate it.

For Windows, you should run .venv\Scripts\activate.

For Mac or Linux, you should run source .venv/bin/activate

Install Python libraries

In the terminal in VS Code, you can install the libraries that we will need for this workshop by running the following commands.

First, if you just created your Python environment, you should upgrade pip, which is the tool that we use to install Python libraries.

pip install --upgrade pip

Now we can install the libraries numpy and matplotlib.

pip install numpy matplotlib

Acknowledgements

These materials borrow heavily from the “Programming with Python” materials by Software Carpentry, which is available under a CC-BY 4.0 license.