Python has APIs that allow us to write both multithreading and multiprocessing applications. The principle behind multithreading and multiprocessing is simply to take copies of our code and run them in additional threads or processes. The operating system automatically schedules the threads and processes across available CPU cores to provide fair processing time allocation to all the threads and processes. This effectively allows a program to simultaneously run multiple operations. In addition, when a thread or process blocks, for example, when waiting for IO, the thread or process can be de-prioritized by the OS, and the CPU cores can be allocated to other threads or processes that have actual computation to do.

Here is an overview of how threads and processes relate to each other:

Threads exist within processes. A process can contain multiple threads but it always contains at least one thread, sometimes called the main thread. Threads within the same process...