Managing Python Dependencies

Python projects often rely on external libraries and packages. pip (Python Package Installer) is the standard tool for managing these dependencies.

Installing Packages

When a virtual environment is activated (as described in the Virtual Environments guide), you can install packages using pip:

pip install requests

This command will download and install the requests library within your active virtual environment.

You can install specific versions of a package:

pip install requests==2.25.1

Or a minimum version:

pip install "requests>=2.20.0"

Listing Installed Packages

To see a list of all packages installed in your active virtual environment, use:

pip list

or

pip freeze

pip freeze is particularly useful for generating a requirements.txt file.

The requirements.txt File

The requirements.txt file is a standard way to specify the dependencies of a Python project. You can generate this file from your active virtual environment:

pip freeze > requirements.txt

This will create a file named requirements.txt containing a list of your installed packages and their versions.

Installing from requirements.txt

To install all the dependencies listed in a requirements.txt file (for example, when setting up a project on a new machine or sharing it with others), you can use:

pip install -r requirements.txt

Keeping Dependencies Up-to-Date

It's good practice to keep your project dependencies up-to-date for security and feature enhancements. You can upgrade a specific package:

pip install --upgrade requests

Or upgrade all outdated packages (though this should be done with caution):

pip install --upgrade -r requirements.txt

By using pip and requirements.txt effectively, you can manage your Python project's dependencies in a consistent and reproducible way. Make sure to use virtual environments (as discussed in Virtual Environments) to isolate these dependencies per project.