The Python Apprentice

The LEGB rule

There are four types of scope in Python, and they are arranged in a hierarchy. Each scope is a context in which names are stored and in which they can be looked up. The four scopes from narrowest to broadest are:

• Local - names defined inside the current function.

• Enclosing - names defined inside any and all enclosing functions. (This scope isn't important for the contents of this book.)

• Global - names defined at the top-level of a module. Each module brings with it a new global scope.

• Built-in - names built-in to the Python language through the special builtins module.

Together, these scopes comprise the LEGB rule:

The LEGB Rule

Names are looked up in the narrowest relevant context.

It's important to note that scopes ...