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Python › Functions & Scope

How does the 'nonlocal' keyword let a nested function modify a variable in its ENCLOSING (not global) scope?

Intermediate

Answer

'nonlocal' tells Python that an assignment inside a nested function should modify the variable in the nearest ENCLOSING function's scope (not create a new local, and not reach all the way to global) — essential for implementing stateful closures, like a counter that persists across calls to an inner function.
def make_counter():
    count = 0
    def increment():
        nonlocal count  # modifies the ENCLOSING 'count', not global or a new local
        count += 1
        return count
    return increment

counter = make_counter()
print(counter())  # 1
print(counter())  # 2
Real-world example Building a stateful closure (like a counter or accumulator) where the inner function needs to persist and modify enclosing state across calls.

Common follow-ups: Why would 'global' NOT work correctly if used instead of 'nonlocal' in this exact scenario?

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