'Get/set the Content-Type header (or None), *without* the
charset or any parameters.
If you include parameters (or ``;`` at all) when setting the
content_type, any existing parameters will be deleted;
otherwise they will be preserved.'

def content_type__get(self):

    header = self.headers.get('content-type')
    if (not header):
        return None
    return header.split(';', 1)[0]
