def _default_checker(x, y):
    """
    Default checker for DualLinker. This checks that the
    variables contain the same data using ==.


    Parameters:
    ----------
    x,y
        the variables to compare data
    """
    if x[0] != y[0]:
        raise Exception('Output mismatch.', {'performlinker': x[0],
            'clinker': y[0]})
