Python Scope

Source: Real Python - Python Scope & LEGB Rule

Python is a dynamically-typed language, so variables come into existence when you assign them.

Python scope determines where names are visible within code. Scopes are implemented as dictionaries called namespaces, which are stored in the .__dict__ attribute.

LEGB

• Local (function) scope - the code block body of any function or lambda expression.
• Enclosing (or nonlocal) scope - special scope that only exists in nested functions.
• Global (module) scope - top-most scope in a Python program, script, or module
• Built-in scope - special python scope that’s created whenever you run a script or open a session.

Modifying scope behavior

Two keywords can be used to modify the content of global and nonlocal names:

1. global
2. nonlocal

The global Statement

Trying to reassign a global variable inside of a local scope will create a new local variable with that name.

To get around this, global can be placed before a variable. global will map any following names (separated by commas) to their global variable counterparts.

The use of global is considered bad practice in general. Usually, if you’re using global a lot there can be a better way to write your code.

The nonlocal Statement

nonlocal is similar to global but on a nested function scale. Inside of a nested function, the nonlocal statement can be used to make a name available in parent functions.