python: local vs global scope

What are the rules for local and global variables in Python?

In Python, variables that are only referenced (and not assigned a value) inside a function are implicitly global.

If a variable is assigned a new value anywhere within the function’s body, it’s assumed to be a local.

If a variable is ever assigned a new value inside the function, the variable is implicitly local, and you need to explicitly declare it with the "global" keyword if you want to use the global context.