Is Open Source Software risky for Software Startups?

Open source code has little to do with patent rights - a patent doesn't rely on the underlying code as much as what it's doing, and open-source usually means the code itself, which would otherwise be subject to copyright and some sort of license. So if, for example, you use an open source python routine, it depends what the routine is for (running a machine, networking connection, etc.) because that might be patented, not whether you coded the function in a different language. The main issue with open source is under which license it's been distributed to you - MIT, Gnu, etc. - and your obligations under that license.