scope

Scope defines where in your program a name (like a variable or function) can be accessed.

“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:

Local (L)

Names defined inside the current function.

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

Enclosing (E)

Names in any enclosing functions, from inner to outer.

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

Global (G)

Names defined at the module level.

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

Built-In (B)

Names preassigned in Python’s built-in namespace, such as common functions and data types.

Python
      
    
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.

Tutorial

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

Understanding Python's variable scope and the LEGB rule helps you avoid name collisions and unexpected behavior. Learn to manage scope and write better code.

intermediate python

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