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Table of Contents
Local (L)
Enclosing (E)
Global (G)
Built-in (B)
Home Backend Development Python Tutorial What is the LEGB (Local, Enclosing, Global, Built-in) rule for scope resolution in Python?

What is the LEGB (Local, Enclosing, Global, Built-in) rule for scope resolution in Python?

Jun 19, 2025 am 12:41 AM
python Scope

Python uses the LEGB rule to resolve variable names in different scopes. 1. Local (L): Variables defined inside the current function. 2. Enclosing (E): Variables in enclosing functions, searched from the inside out. 3. Global (G): Variables defined at the top level of a module or declared global. 4. Built-in (B): Predefined names like built-in functions and exceptions. Understanding and following this lookup order helps avoid scope-related bugs and ensures proper variable access.

What is the LEGB (Local, Enclosing, Global, Built-in) rule for scope resolution in Python?

Python uses the LEGB rule to determine which variable you're referring to when there are multiple variables with the same name in different scopes. This rule defines the order in which Python looks up variable names.

Here’s how it works:

Local (L)

This refers to variables defined inside the current function. When you assign a variable inside a function, it's considered local to that function by default.

For example:

def my_func():
    x = 10  # x is local to my_func
    print(x)

my_func()

Trying to access x outside of my_func() will result in an error because it only exists in the local scope.

Enclosing (E)

This applies to nested functions. If a variable isn't found in the local scope, Python checks any enclosing functions from the inside out.

Example:

def outer():
    y = 20
    def inner():
        print(y)  # y is in the enclosing scope
    inner()

outer()

In this case, inner() can access y because it was defined in the outer function.

Global (G)

Variables defined at the top level of a module or declared as global inside a function fall into this category.

Example:

z = 30  # global variable

def show_z():
    print(z)  # can access global variable

show_z()

If you want to modify a global variable inside a function, you must use the global keyword:

  • global z
  • Then you can assign a new value like z = 50

Built-in (B)

These are special names that Python provides, like built-in functions and exceptions (print, len, TypeError, etc.).

You can accidentally override these if you're not careful:

def len():  # Not a good idea!
    return "I overrode len!"

print(len())  # Now this breaks normal behavior

To avoid issues:

  • Don’t name your variables after built-in functions.
  • Use tools like linters or IDEs to warn about such conflicts.

So, the LEGB rule helps Python decide where to look for a variable:

  • First check Local,
  • Then Enclosing,
  • Then Global,
  • And finally Built-in scopes.

It’s not magic, just a clear lookup order. Keep your naming clean and understand where each variable lives, and you’ll avoid most scope-related bugs.

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