how does CPython work?

[beliavsky at aol.com]

The book "Learning Python" says that a "Python Virtual Machine"
interprets "byte code" to run a Python program. Is there a book or
site that describes in more detail what Python is doing behind the
scenes? One reason for my question is that I want to better understand
what kinds of Python programs run relatively fast or slow, rather than
relying solely on trial and error.