I notice when I run my heavily CPU dependant python programs, it only uses a single core. Is it possible to assign multiple cores to the program when I run it?
You have to program explicitly for multiple cores. See the Symmetric Multiprocessing options on this page for the many parallel processing solutions in Python. Parallel Python is a good choice if you can't be bothered to compare the options, look at the examples here.
Some problems can't take advantage of multiple cores though. Think about how you could possibly run up the stairs faster with the help of three friends. Not going to happen!
If any part of your problem can be run in parallel, you should look into the multiprocessing module
I wonder why nobody mentioned CPython's GIL (Global Interpreter Lock) yet. It basically means that multiple threads inside one Python interpreter cannot use the power of multiple cores because many operations are protected by a global lock in order to be thread-safe. This only applies to a small amount of applications - the CPU-bound ones. For more info, just search for the term "GIL", there are already many questions on it (like that one, for example).
This answer of course assumes that you are in fact using multiple threads, or else you won't be able to use multiple cores anyway (multiprocessing would be another possibility).
来源：https://stackoverflow.com/questions/4519951/assigning-multiple-cores-to-a-python-program