numpy array与list

[fanx042]

    def calc_histogram_(self, gray_arr, level = 256):
        ### calculate the histogram of a gray scale image
        ### @params gray_arr : numpy.array uint8 type, 2-dim
        ### @params level : the level of gray scale
        ### @return hists : list type
        hists = [0 for _ in range(level)]
        for row in gray_arr:
            for p in row:
                hists[p] += 1
        return hists`

    def clip_histogram_(self, hists, threshold = 10.0):
        ### clip the peak of histogram, and separate it to all levels uniformly
        ### @params hists : list type
        ### @params threshold : the top ratio of hists over mean value
        ### @return clip_hists : list type
        all_sum = sum(hists)
        threshold_value = all_sum / len(hists) * threshold
        total_extra = sum([h - threshold_value for h in hists if h >= threshold_value])
        mean_extra = total_extra / len(hists)
        
        clip_hists = [0 for _ in hists]
        for i in range(len(hists)):
            if hists[i] >= threshold_value:
                clip_hists[i] = int(threshold_value + mean_extra)
            else:
                clip_hists[i] = int(hists[i] + mean_extra)
        
        return clip_hists

这些函数，在明确使用numpy的前提下，为什么还有这么多的List的操作呢？