def make_di_block(dec, inc):
    """
    Some pmag.py and ipmag.py functions require or will take a list of unit
    vectors [dec,inc,1.] as input. This function takes declination and
    inclination data and make it into such a nest list of lists.

    Parameters
    -----------
    dec : list of declinations
    inc : list of inclinations

    Returns
    -----------
    di_block : nested list of declination, inclination lists

    Example
    -----------
    >>> decs = [180.3, 179.2, 177.2]
    >>> incs = [12.1, 13.7, 11.9]
    >>> ipmag.make_di_block(decs,incs)
    [[180.3, 12.1, 1.0], [179.2, 13.7, 1.0], [177.2, 11.9, 1.0]]
    """
    di_block = []
    for n in range(0, len(dec)):
        di_block.append([dec[n], inc[n], 1.0])
    return di_block
