def METHOD_NAME(self,name,value):
    """Return first matching header value for 'name', or 'value'
    If there is no header named 'name', add a new header with name 'name'
    and value 'value'."""
    result = self.get(name)
    if result is None:
        self._headers.append((self._convert_string_type(name),
            self._convert_string_type(value)))
        return value
    else:
        return result