Instead of using ```get```, returning "unknown", and then checking if you received "unknown", I recommend rewriting as:

```
try:
    self.Type = self.api_mapping[self.Type]
except KeyError:
    raise IncompetentDeveloperError("Unsupported Type in HTMLInterfaceOption: %s" % original_type)
```

Also note that the ```str``` conversion in your error message formatting is unnecessary.