nonlocal

The 'nonlocal' keyword in Python is a statement used to declare that a variable inside a nested function refers to a variable in the nearest enclosing scope that is not global. It allows nested functions to modify variables from their parent functions, enabling mutable state across function boundaries without using global variables. This is essential for closures and maintaining state in functional programming patterns within Python.

Also known as: nonlocal keyword, nonlocal statement, Python nonlocal, nonlocal variable, nonlocal declaration

Why learn nonlocal?

Developers should learn 'nonlocal' when working with nested functions or closures where they need to update variables from an outer (non-global) scope, such as in decorators, stateful generators, or callback functions. It's particularly useful in functional programming to avoid side effects with global variables and to create more modular and maintainable code by encapsulating state within specific scopes.

Learning Resources

• docs: Python Documentation: nonlocal statement
• tutorial: Real Python Tutorial: Python Scope & the LEGB Rule
• tutorial: GeeksforGeeks: nonlocal keyword in Python
• video: YouTube: Python nonlocal Keyword Explained
• tutorial: W3Schools: Python nonlocal Keyword