Upload a file or files to web service when opening URL with Python

I regularly use a web service where I can drag-and-drop files to convert them to another format. I wonder if I could make a python script (or use other language) to do open a URL with some files.

The reason for my question is that I have an Apple Automator framework where I pick some files based on 'FolderAction', sort them to appropriate folders and also automatically open URL with 'GPX to TCX' conversion. But then I need to manually drag-and-drop selected files and convert them with the service + download the files (I can record UI action to automate this but it tends to be unreliable).

Would be great if I could do it all from a script. So: having some GPX files supplied to i.e.g, python script and URL of the service and somehow parse the files together with URL. I tried to read URLLIB and URLLIB2 for some insights but I still have no clue if I could use any of these. So far my python use for strict scientific with NumPy and SciPy.

I have no idea if this is even possible but I figured if you can just drag-and-drop files maybe you could parse them somehow with URL.

I would appreciate some feedback.

If this is not possible in Python but is possible with other language I'd appreciate guidance too.