Unpacking into function call

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*nums unpacks the list into three positional arguments, so add(1, 2, 3) returns 6. add(1, 2, **opts) unpacks opts as keyword arguments, passing c=10, so the call becomes add(1, 2, c=10) which returns 13. The second call would raise a TypeError if opts contained a key that isn't a parameter name - Python validates keyword argument names at call time. These unpacking operators are especially handy when forwarding arguments from one function to another.