> Why are you adding `.as_uri()`?

The API we provide accepts URIs, so whilst the example seems a little contrived, the code itself expects a URI and then calls open (making use of the ability to add open handlers).

> Builtin open() calls C open().

As best I can tell the file handler is defined in urllib/request.py as file_open.  This appears to do some preprocessing to remove the file scheme and (and explicitly throws an exception if there's a host that isn't localhost) before it gets to the C open().  I wondered why it didn't check if it was on windows and, if so, construct an appropriate path (since quadruple hash I don't think adheres to the URI RFC, but seems to open correctly)?