def stringify_key_values(dicts, keys=None):
    """
    Convert the dict values of a list of dicts to strings. If keys are specified, 
    only convert specified key values to strings.
    """
    if keys:
        stringified = []
        for _dict in dicts:
            new_dict = {}

            for k in _dict.keys():
                if k in keys:
                    new_dict[k] = str(_dict[k]).strip()

                else:
                    new_dict[k] = _dict[k]

            stringified.append(new_dict)

        return stringified

    else:
        return [{k: str(v).strip() for k, v in record.items()} for record in dicts]