Python environment

Our project uses libraries in addition to Python itself. A virtual environment keeps those libraries together for this project so they don’t clash with other programs on your computer. Ours is a folder named .venv inside Chiron.

Why use one?¶

Your first print program works without an environment. We use one because Chiron and another robot project might need different RobotPy versions. Installing one project’s packages should not replace the other’s. Python’s virtual-environment guide explains this separation.

The environment runs locally using the Python version you created it with. It doesn’t create a virtual computer or simulate the robot. Activation just makes this terminal find the environment’s Python when you type python. Your .py files stay in student-work; they are not stored inside .venv. Git ignores the environment because it can be recreated from the package list.

There are three separate jobs: create the environment once, install the listed libraries into it, then activate it when starting a new terminal.

Create and Install¶

Open Chiron in VS Code. Run these lines one at a time, waiting for each to finish. The terminal should be in the folder containing requirements.txt. That file lists the exact library versions for this course. If you aren’t sure you have the right folder, look for it in VS Code’s Explorer and open a fresh terminal with Terminal → New Terminal. Stop after any failed command; later steps depend on it succeeding.

py -3.14 -m venv .venv

.venv\Scripts\activate.bat

python -m pip install -r requirements.txt

python3.14 -m venv .venv
source .venv/bin/activate
python -m pip install -r requirements.txt

Installation downloads packages and can take several minutes. Wait until the terminal’s prompt returns. A successful install reports installed packages or that they are already satisfied; a red error needs attention before continuing. You can rerun the same install command after fixing a connection problem. A notice offering a newer pip version is not itself an installation failure.

-m venv asks Python to run its environment-creation tool. -m pip install -r asks the new environment to install the packages listed in a file. You aren’t expected to memorize these flags; the commands are here for reference.

In the Command Palette choose Python: Select Interpreter and select .venv. An interpreter is the program that executes Python. Selecting one tells VS Code which Python to use. VS Code may also activate it in new terminals, but let’s check instead of assuming it did.

If .venv is not listed, choose Enter interpreter path and browse to .venv/Scripts/python.exe on Windows or .venv/bin/python on macOS/Linux.

Check Python¶

Run this in the terminal you plan to use for the lesson:

python -c "import sys; print(sys.executable)"

The path should end in Chiron\.venv\Scripts\python.exe on Windows or Chiron/.venv/bin/python on macOS/Linux. Your parent folder may be different. The important part is this project’s .venv. If another Python appears, activate the environment using your operating-system tab above, then check again.

You can now use the short python commands throughout the course. If a later lesson says a library is missing, repeat this check before reinstalling anything.

Check Environment¶

Using the environment’s Python as explained in the tabs, run:

python --version
python -m pip check
python -c "import wpilib, commands2; print('RobotPy is ready')"
python tools/start_exercise.py foundations
python student-work/foundations/main.py

Expected: Python 3.14.7, No broken requirements found., RobotPy is ready, a message saying the exercise was created, and Hello, Spartronics!. The helper copies starter files into student-work/foundations. The maintained originals stay in examples, and your copies are yours to edit. If you run the copy command twice it refuses to overwrite your first attempt.

If a command reports “no such file”, check the terminal’s folder and the path. If it reports “No module named ...”, check which Python you used. Keep the command and complete error message together in your notes so you can compare the result after each change. The table below covers the common setup problems.

Next Time¶

1. In VS Code, choose File → Open Recent and your existing Chiron folder.

2. Open a terminal. On Windows choose Command Prompt, then run .venv\Scripts\activate.bat. On macOS/Linux run source .venv/bin/activate.

3. Run the lesson’s python ... command from the Chiron root. If there is any doubt about the interpreter, use Check your Python.

That’s all you need for a normal session. Don’t recreate the environment or copy an exercise again to resume working on it. Open your existing assignment. Closing the terminal ends activation; it does not remove packages or your work.

Try one edit¶

Open student-work/foundations/main.py in Explorer. Change the greeting inside the quotation marks, save, and run it again. Confirm the new greeting appears. We’ll explain every part of that line in the first Python lesson.

Next: save your first Git checkpoint.