scope

“LEGB” Rule

Python uses lexical scoping with the LEGB rule. The letters in the acronym LEGB stand for Local, Enclosing, Global, and Built-in scopes. This summarizes not only the Python scope hierarchy but also the sequence of steps that Python follows when resolving names in a program:

def my_func():
    x = 1  # Local scope
    print(x)

def outer():
    x = 1
    def inner():
        print(x)  # Can access enclosing scope
    inner()

x = 1  # Global scope
def my_func():
    print(x)  # Accesses global x

def my_func():
    items = [1, 2, 3]
    length = len(items)  # 'len' is from built-in scope
    return str(length)   # 'str' is from built-in scope

Key Points

• Python creates a new scope when defining a function or class
• The global keyword lets you modify global variables from within functions
• The nonlocal keyword lets you modify variables in an enclosing (but not global) scope
• List comprehensions create their own scope for the iterator variable

Remember that classes create their own namespaces, but not their own nested scope in the same way functions do.

Related Resources

Tutorial

Python Scope & the LEGB Rule: Resolving Names in Your Code

In this step-by-step tutorial, you'll learn what scopes are, how they work, and how to use them effectively to avoid name collisions in your code. Additionally, you'll learn how to take advantage of a Python scope to write more maintainable and less buggy code.

intermediate python

For additional information on related topics, take a look at the following resources:

• Python Inner Functions: What Are They Good For? (Tutorial)
• Namespaces and Scope in Python (Tutorial)
• Python Inner Functions (Course)
• Navigating Namespaces and Scope in Python (Course)
• Namespaces and Scope in Python (Quiz)