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Python Modules, pip and Virtual Environments (venv) Explained for Beginners

P10.5 How to Use requirements.txt in Python Projects

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Why. A teammate in another city must run your project with the same package versions. requirements.txt lists them.

What. A text file with one package per line, often with versions. pip freeze writes it; pip install -r reads it.

How.

Share your environment

  1. Activate the venv.
  2. Run python -m pip freeze > requirements.txt.
  3. Commit the file to Git (not the .venv folder).
  4. The teammate creates a venv and runs python -m pip install -r requirements.txt.

Worked example A — Save and reinstall.

Step 1 — What we do. Freeze the packages, then install them on another laptop.

Step 2 — Type and run this code.

python -m pip freeze > requirements.txt
python -m pip install -r requirements.txt

Step 3 — What it means. The first line saves exact versions; the second recreates them anywhere.

Worked example B — Read a requirements file with Python.

Step 1 — What we do. We count packages listed in a requirements file.

Step 2 — Make the input file requirements.txt in the same folder as your code:

# data project
numpy==2.1.0
pandas==2.2.2
matplotlib==3.9.2

About this data: each non-comment line is one package and its exact version.

Step 3 — Type and run this code.

with open("requirements.txt", encoding="utf-8") as f:
    pkgs = [l.strip() for l in f if l.strip() and not l.startswith("#")]
print(len(pkgs), "packages:", pkgs)

Step 4 — Output you should see.

3 packages: ['numpy==2.1.0', 'pandas==2.2.2', 'matplotlib==3.9.2']

Step 5 — What it means. It is just a text file — you already know how to read it.

Ravindra Bagale's Tip

Add .venv/ to your .gitignore. Share requirements.txt, never the venv folder itself.