You can use the selenium webdriver to access and navigate websites. You can also use BeatifulSoup to scrape and identify downloads. Using these packages together will solve your problem.
Here is an example of working code using these packages to automate the download of ...
how are the arc geometries are defined in your dataset. Generally the arc geometries are defined differently in respective GIS formats.
If the arcs are defined as tiny segments of linear objects, shapely should handle this.
If the arcs are defined using angle and radius then it needs to be simplified into tiny linear objects and pass into shapely.