Get all parameters associated with a ParameterGroup

        :type groupname: str
        :param groupname: The name of the DBParameter group to retrieve.

        :type source: str
        :param source: Specifies which parameters to return.
                       If not specified, all parameters will be returned.
                       Valid values are: user|system|engine-default

        :type max_records: int
        :param max_records: The maximum number of records to be returned.
                            If more results are available, a MoreToken will
                            be returned in the response that can be used to
                            retrieve additional records.  Default is 100.

        :type marker: str
        :param marker: The marker provided by a previous request.

        :rtype: :class:`boto.ec2.parametergroup.ParameterGroup`
        :return: The ParameterGroup

def get_all_dbparameters(self, groupname, source=None,
                             max_records=None, marker=None):
        """
        Get all parameters associated with a ParameterGroup

        :type groupname: str
        :param groupname: The name of the DBParameter group to retrieve.

        :type source: str
        :param source: Specifies which parameters to return.
                       If not specified, all parameters will be returned.
                       Valid values are: user|system|engine-default

        :type max_records: int
        :param max_records: The maximum number of records to be returned.
                            If more results are available, a MoreToken will
                            be returned in the response that can be used to
                            retrieve additional records.  Default is 100.

        :type marker: str
        :param marker: The marker provided by a previous request.

        :rtype: :class:`boto.ec2.parametergroup.ParameterGroup`
        :return: The ParameterGroup
        """
        params = {'DBParameterGroupName' : groupname}
        if source:
            params['Source'] = source
        if max_records:
            params['MaxRecords'] = max_records
        if marker:
            params['Marker'] = marker
        pg = self.get_object('DescribeDBParameters', params, ParameterGroup)
        pg.name = groupname
        return pg