From the python source code: https://github.com/python/cpython/blob/11749e2dc20ad6a76e9a39e948853e89b2b4bbed/Lib/webbrowser.py#L619 https://github.com/python/cp

From the python source code: https://github.com/python/cpython/blob/11749e2dc20ad6a76e9a39e948853e89b2b4bbed/Lib/webbrowser.py#L619 https://github.com/python/cpython/blob/11749e2dc20ad6a76e9a3... It seems to be shelling out to osascript, either telling it to OpenURL or open.