The full trace: python3 hello.py

One command, every concept

You type python3 hello.py and press Enter. Here is the whole story, and you have already learned every step:

1. The shell reads your keystrokes. It is just a user-space process, blocked on a read syscall from the keyboard (lessons 6-2 and 8-1).
2. The shell asks the kernel for a child process and has it load the python3 program from disk into RAM (lessons 3-3 and 1-1). The kernel builds a process: fresh PID, a brand-new page table mapping its private virtual address space, empty stack and heap, entry in the process table (lessons 3-1, 3-2, 4-1, 4-4).
3. The scheduler starts giving it time slices (lesson 6-1). The CPU begins the fetch-decode-execute cycle on Python's instructions (lesson 1-2).
4. Python reads hello.py with open/read syscalls, byte by byte, decoding UTF-8 into text (lessons 7-1, 2-3), and starts interpreting it.

...and the ending

1. hello.py calls print("Hello!"): the text goes to a buffer, the newline flushes it, the write syscall crosses into the kernel, the bytes land in file descriptor 1, the terminal draws glyphs (lessons 7-2, 8-2).
2. The script ends. Python exits with code 0. (Had it hung, Ctrl-C would have delivered SIGINT, lesson 3-4.) The kernel frees the process's memory and page table, closes its descriptors, removes the process-table entry, and hands the exit code to the parent, the shell (lessons 3-3, 3-4, 4-3, 4-4).
3. The shell wakes up (it was blocked waiting for its child), sees exit code 0, and prints the next prompt.

Elapsed time: maybe 30 milliseconds, containing thousands of context switches system-wide, and every single mechanism in this course.