HttpResponse.__init__(content='', content_type=None, status=200, reason=None)
Instantiates an HttpResponse object with the given page content and content type.
...
content_type is the MIME type optionally completed by a character set encoding and is used to fill the HTTP Content-Type header. If not specified, it is formed by the DEFAULT_CONTENT_TYPE and DEFAULT_CHARSET settings, by default: “text/html; charset=utf-8”.

Historically, this parameter was called mimetype (now deprecated).