ScopedRateThrottle support for function based views

[d-ryzhykau]

Currently it's impossible to use ScopedRateThrottle with function based views. There was a workaround suggestion, but as the author stated it's rather nasty.

It's possible to add ScopedRateThrottle support for function based views by implementing the following changes:

1. Add a throttle_scope decorator that would set a throttle_scope attribute on the view func, following the pattern of other decorators like throttle_classes.
2. Change the inner api_view.decorator function to copy the the throttle_scope attribute from the view func to the WrappedAPIView class.

Would the project maintainers accept such change? If so, I'll be glad to contribute it to the project.

[cookesan]

The shape you propose matches how the existing function-based view decorators work.

ScopedRateThrottle only needs the view object to have throttle_scope. @api_view already copies attributes such as renderer_classes, parser_classes, authentication_classes, throttle_classes, and permission_classes from the function onto the generated WrappedAPIView; it just does not copy throttle_scope.

A focused change could be:

def throttle_scope(scope):
    def decorator(func):
        _check_decorator_order(func, "throttle_scope")
        func.throttle_scope = scope
        return func
    return decorator

and then in api_view.decorator:

WrappedAPIView.throttle_scope = getattr(func, "throttle_scope", None)

I cannot say whether maintainers will accept it, but it is small, follows the existing decorator pattern, and should be easy to test. I would include docs showing decorator order with @api_view, plus a test that ScopedRateThrottle applies to an FBV only when @throttle_scope(...) is present.