Learn about the basics of object oriented code through python, and learn about the basics of computer science through C. When you're at least pretty okay with both of those other languages learn C++, because you can do pretty much anything in C++ and make it run quickly (though it takes forever to write).
So, here's the thing: for your first project you'll be in somebody's lab working on somebody else's code. In which case they'll be the one choosing the programming language. Which I personally think is kind of great!
I mean, as a beginner you're not really going to know your ass from you elbow for a while, and, especially when you don't know what you're doing, learning to program can be borrring. Thus, it's good to have the structure and limits that come from working on somebody else's code, and it's good to have the motivation and excitement that can only come from working on a real project.
Still, regardless of whatever language your lab uses (especially if it's Matlab), you should probably learn python, C, and C++. In particular, if you're not coming from a computer science background you MUST read Kernighan and Ritchie's "The C Programming Language". It's 35 years old and gives the distinct impression that its authors were programming on punch cards, but it is that rarest of birds: a timeless computer science book. It will make many things a great deal clearer.