Summary
Modern operating systems sandbox each process inside of a virtual memory map from which direct I/O operations are generally impossible. Instead, a process has to ask the operating system every time it wants to modify a file or communicate bytes over the network. By using operating system specific tools to watch the system calls a Python script is making -- using "strace" under Linux or "truss" under Mac OS X -- you can study how a program is behaving and address several different kinds of bugs.