I need to store configurations (key/value) for a Python application and I am searching for the best way to store these configurations in a file.
I run into Python\'s
This entirely depends on your requirements. If (as you say) all you need is key/value pairs, ini files (or other "plain" config files) will perfectly suit you. No, they are not outdated, as they are still in use.
XML/JSON is perfect if you have hierarchical structures and also want to use more sophisticated methods (e.g: XML file validation, namespaces, etc.).
Check out ConfigObj, its the slickest method I've found so far, and definitely more flexible than ConfigParser. Personally I'm not a fan of YAML based because its 'flexibility' makes it difficult to use with tools like Augeas.