I also need to make sure no other user can open the file and read and/or write to it while the process is taking place for another user running it. What are the exact steps needed to take in order to accomplish this?

That depends on your OS/filesystem. If you have mandatory locking, just require an exclusive lock. Otherwise, you may need do drastic measures like dropping the run level so the OS runs in single user mode. Or by hacking the kernel sources, recompiling and installing the changed kernel. Of course, if you own the file, removing write access for everyone else easily accomplishes the task.