Got one dollar to spare? This might be easier than you think.
Say a bit more about your use case...
Especially, do you want to scan barcodes that you create or do you want to scan preexisting barcodes? If you are creating your own barcodes, you should be able to get ZBar to automatically launch your own Pythonista scripts for free using the Pythonista URL Scheme. See: http://omz-software.com/pythonista/docs/ios/urlscheme.html
You should also push the ZBar community to adopt a zbar:// style for launching their app so that you can launch ZBar directly from Safari or your Pythonista scripts. See: http://x-callback-url.com , http://handleopenurl.com , http://handleopenurl.com/search?scheme=bar -- This last one makes it seem like other barcode apps for iOS already have handleopenurl capabilities that you might want to play with.
Scanner Go http://ilevelupapps.com/scanner-go might be a great place to start your search as it is built on the ZBar engine and already supports the bi-directional x-callback-URL. It will cost you a buck in the iTunes Store but that is cheap.
import webbrowser; webbrowser.open('ilu://')
will cause Pythonista to launch Scanner Go. See: http://ilevelupapps.com/scanner-go/scanner-go-protocol for getting Scanner Go to automatically pass the resulting barcode data back into your Pythonista script.