Closures: inner functions that remember variables from an enclosing scope, and late binding

Python lets you define a function inside another function. The inner function can read variables of the outer function, because name lookup follows the LEGB rule: Local, then Enclosing function scopes, then Global, then Built-in. A closure is created when the outer function returns the inner function and the inner one still uses variables from the outer scope. Even though the outer function has finished, the returned function keeps those variables alive and can use them whenever it is called.