This tool written in Python language will help you automatically download LANDSAT data form the USGS earthexplorer web site. It was primarily included in CESBIO Multitemp blog, then moved here for a better convenience.
There is a short user manual here :
You may directly read the code here :
Finally, the THEIA Land Data Center also distributes all the LANDSAT8 data acquired above France, with an accurate cloud mask and a good atmospheric correction. You can access them here :
I have also written a much simpler tool to get ESA Sentinel data.