Get updated values from 2 dicts of values

    Args:
        before_values (dict): values before update
        after_values (dict): values after update

    Returns:
        dict: a diff dict with key is field key, value is tuple of
              (before_value, after_value)

def _get_updated_values(before_values, after_values):
    """ Get updated values from 2 dicts of values

    Args:
        before_values (dict): values before update
        after_values (dict): values after update

    Returns:
        dict: a diff dict with key is field key, value is tuple of
              (before_value, after_value)
    """
    assert before_values.keys() == after_values.keys()
    return dict([(k, [before_values[k], after_values[k]])
                 for k in before_values.keys()
                 if before_values[k] != after_values[k]])