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Virtual Environments & pip, Briefly

4 min read

You'll learn to

-Explain what a virtual environment is and why it isolates a project's dependencies
-Use `pip install` to add a third-party package to a project
-Know that none of this is needed inside the Forge Algorithm Lab sandbox itself

This chapter is intentionally short. It is a practical aside about the Python ecosystem outside of ScaleDojo, not a deep topic. The Forge Algorithm Lab's browser-based sandbox already has everything you need pre-installed and does not require (or allow) installing packages, so nothing here is required for lab levels. It matters for being a competent Python developer everywhere else.

The Problem: Every Project Wants Different Versions

If you work on two different Python projects on the same machine, they might need different versions of the same third-party library. One needs an old version, the other needs the newest. Installing packages globally, system-wide, means you cannot satisfy both at once. A virtual environment (a "venv") solves this by giving each project its own private, isolated set of installed packages, completely separate from every other project on the machine.

Creating and Using a Venv

Typical venv commands (run in a terminal, not in Python itself)

# Create a virtual environment in a folder named "venv"
# python -m venv venv

# Activate it (this changes which "python" and "pip" your terminal uses)
# On macOS/Linux:  source venv/bin/activate
# On Windows:       venv\Scripts\activate

# Install a package into the active venv, not system-wide
# pip install requests

# See what's installed in this venv
# pip freeze

Once a venv is active, pip install some-package installs it only into that isolated environment. Your other projects, and your system-wide Python, are unaffected. Deactivating (deactivate) returns you to your normal system Python.

A project's dependencies are usually recorded in a requirements.txt file, one package per line, for example requests==2.31.0, which lets anyone recreate the same environment with pip install -r requirements.txt. ScaleDojo's own backend uses exactly this file.

-A venv isolates a project's installed packages from every other project and from the system Python.
-pip install <package> adds a third-party package; pip freeze lists what is currently installed.
-None of this applies inside the Forge Algorithm Lab itself. Its sandbox is pre-configured and does not install or need packages, but it is essential knowledge for writing Python anywhere else.

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