What a closure is

Question

What a closure is

Accepted Answer

When a nested function references a variable from its outer function, Python keeps that variable alive in the closure's __closure__ attribute, even after the outer call finishes. This lets you build stateful functions without classes - make_counter() returning a counter() that increments its own n is the classic example. The tricky part is that closures capture variables by reference, not value, which is why the late-binding loop bug catches people off guard.