You don’t need to write a script for that. There’re some tools that you can use depending on your OS:
Linux
xdg-open is available in most Linux distributions. It opens a file or URL in the user’s preferred browser (configurable with xdg-settings).
xdg-open https://stackoverflow.com
macOS
open opens files and URLs in the default or specified application.
open https://stackoverflow.com
open -a Firefox https://stackoverflow.com
Windows
You can use the start command at the command prompt to open an URL in the default (or specified) browser.
start https://stackoverflow.com
start firefox https://stackoverflow.com
Cross-platform
The builtin webbrowser Python module works on many platforms.
python3 -m webbrowser https://stackoverflow.com