import math


def diffs(l1, l2):
    """Returns the element-wise differences between two lists.

    Raises
    ------
    ValueError
        If 2 lists of different length are passed.
    """
    if len(l1) != len(l2):
        raise ValueError("Pass 2 lists of equal length.")
    return [math.fabs(a - b) for a, b in zip(l1, l2)]