This question is intended as a canonical that gathers the important, overlapping ideas from several Stack Overflow questions. The goal is to create a clear overview of Python's model for starting the execution of code.

The question is notably not about:

• importing code (except to the extent that the initially run script file is loaded by a process similar to importing);
• managing multiple versions of Python (e.g. controlling which installation python, python3 etc. refer to);
• understanding the Python Launcher for Windows (beyond what's necessary to understand running a Python script);
• understanding or dealing with virtual environments (except insofar as they impact the launch process);
• Windows 10's wrapper program that promotes installing Python from the Microsoft Store.

Reference questions on Stack Overflow that inspired this question:

• Why do people write #!/usr/bin/env python on the first line of a Python script?
• How do I make a python script executable?
• ./xx.py: line 1: import: command not found

• How do I run a Python program?
• How do I run my Python script? Why does the command line tell me "no such file or directory"?

• What does if __name__ == "__main__": do?
• Run function from the command line
• Why is Python running my module when I import it, and how do I stop it?
• Why doesn't the main() function run when I start a Python script? Where does the script start running (what is its entry point)?