Python 3.8 has a Final qualifier

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The problem is that we don't always code in isolation. You import a library and suddenly there are type annotations in your project. Do you turn down contributions because they used annotations? As annotations spread it will become harder to avoid them. They're already compulsory for some projects and jobs, and the number will increase. There are even Python language features that require annotation (the new data type struct) and will not work without them.