global and nonlocal Keywords & Variable Binding

1Concept

`global` binds a variable inside a function to the module-level namespace. `nonlocal` binds to the nearest enclosing non-global scope, enabling stateful closures without object orientation.

2Architecture Diagram

def outer():
  count = 0
  def inner():
    nonlocal count ---> Mutates count in enclosing frame!
    count += 1

3Code Example

def make_counter(initial: int = 0):
    count = initial
    def increment(step: int = 1) -> int:
        nonlocal count
        count += step
        return count
    return increment

counter = make_counter(10)
print(f"Counter Step 1: {counter(5)}")
print(f"Counter Step 2: {counter(2)}")

4Expected Output

Counter Step 1: 15
Counter Step 2: 17

5Key Takeaways

• ✓`nonlocal` cannot be used at module level; it requires an enclosing function scope.
• ✓`global` makes code difficult to test and maintain; avoid in concurrent systems.
• ✓Closures with `nonlocal` provide lightweight encapsulation alternative to single-method classes.