Python Nested Functions and Closures Explained

Nested Functions

def outer(x):
    def inner(y):
        return x + y
    return inner

add5 = outer(5)
print(add5(10))   # 15

What Is a Closure?

A closure is a function that remembers variables from its surrounding scope, even after the outer function has returned.

Why Use Them?

• Creating customised functions on the fly.
• Encapsulating state without a class.
• Callback factories.

Counter Example

def make_counter():
    count = 0
    def inc():
        nonlocal count
        count += 1
        return count
    return inc

c = make_counter()
print(c(), c(), c())   # 1 2 3