Decorator capturing state via closure

Question

Accepted Answer

The `calls` variable lives in the enclosing scope of `wrapper` - it is shared across all calls because there is only one closure created at decoration time. Each call to `ping()` increments the same `calls` counter and prints its current value. You need `nonlocal calls` to reassign a variable from an enclosing scope; without it, Python would treat `calls` as a local and raise an `UnboundLocalError`.