def euclidean_distance(histo1, histo2):
    """
    Euclidean distance between two histograms

    :param histo1:
    :param histo2:
    :return:
    """
    val = 0
    lnot = []
    for w in histo1:
        if w in histo2:
            val += (histo1[w] - histo2[w]) ** 2
            lnot.append(w)
        else:
            val += histo1[w] * histo1[w]
    for w in histo2:
        if w not in lnot:
            val += histo2[w] * histo2[w]
    return val
