Learn how to use startup configuration files to run package entry points when the Python interpreter starts up.A startup configuration file is a file with the extension .start.Starting from Python 3.15, the Python interpreter uses startup configuration files to run package entry points when the interpreter starts up.Here is an example of a simple startup configuration file that installs error-links when the Python interpreter starts:error_links:installThe entry point error_links:install from the above points to the function install from the module error_links.In general, an entry point resembles an import:the import pathfollowed by a colonfollowed by the callable that gets calledFor the entry point error_links:install, the equivalent import would be from error_links import install.The module site and some historical contextThe module site, from the standard library, is imported automatically when the Python interpreter starts up.When imported, the module site does a couple of things.Among them, it adds some paths to the module search path and then checks them for configuration paths.In Python 3.14 or earlier, configuration files were .pth files..pth files can be used to extend sys.path by listing directories.Alongside that, and for backwards compatibility reasons, .pth files could also include import lines.import lines in a .pth represent a security risk, so PEP 829 introduced a safer way of running custom hooks during Python interpreter start up.import lines in .pth files are now deprecated and Python 3.15+ also looks for .start files to run the listed entry points.Python 3.15 brings much more to the tableFrom the two new built-ins frozendict and sentinel, to lazy imports, package startup configuration files, typing improvements, or more colour everywhere, Python 3.15 has a lot more to offer.If you want to learn more about what's new in Python 3.15, take a look at the “15 days of Python 3.15” series I'm running.For 15 days, I'll explain a new Python 3.15 feature every day.Get the free 3.15 email series: