To send a WhatsApp message using Python, developers need to set up their local environment with the necessary dependencies, including Python 2 or 3, a free Twilio account with activated WhatsApp Sandbox, and the Twilio Python Helper Library. They also need to export their Twilio credentials as environment variables, which can be done by copying the Account SID and Auth Token and running specific commands in the terminal. Once the environment variables are set, developers can write a Python script that uses the Twilio API to send a WhatsApp message with a specified body, from number, and to number. The script can be activated and tested using the Twilio Console's WhatsApp page, which provides instructions on how to connect to the sandbox by sending a WhatsApp message through a device. With this setup, developers can successfully send WhatsApp messages using Python.