How to install Python packages with pip and requirements.txt

Installing Python packages using pip and a requirements.txt file is a common practice, especially when setting up environments for projects. Here’s a step-by-step guide:

1. Install Python and pip

Before you can install packages, ensure that Python and pip are installed on your system. Most systems come with pip pre-installed, but you can verify by running:

python --version
pip --version

If pip is not installed, you can install it using the following command:

python -m ensurepip --upgrade

2. Create or obtain a requirements.txt file

A requirements.txt file lists all the Python packages required for a project, along with their versions. You can create one manually, or it may be provided with the project you're working on.

Example of a requirements.txt file:

numpy==1.21.0
pandas>=1.3.0
requests

This file specifies the exact version for numpy, a minimum version for pandas, and the latest version for requests.

3. Install packages using pip

To install the packages listed in a requirements.txt file, use the following command:

pip install -r requirements.txt

This will install all the packages and dependencies specified in the file.

4. (Optional) Create a requirements.txt file from existing environment

If you want to create a requirements.txt file from the packages already installed in your environment, use:

pip freeze > requirements.txt

This command lists all installed packages and their versions in the requirements.txt file.

5. Verify installation

After installation, you can verify that the packages are installed by checking them with:

pip list

This command lists all installed packages and their versions in your environment.

Summary

• Ensure Python and pip are installed.
• Use requirements.txt to manage project dependencies.
• Install packages using pip install -r requirements.txt.
• Optionally, generate a requirements.txt file using pip freeze.

This approach ensures that your project’s environment is consistent across different systems.