存储数字在 -255 到 255 之间的 numpy 数组的最小方法？

Question

What is the way to store this array that takes up the least amount of memory? uint8 doesn't work since some values are negative and int8 doesn't work since some values are above 127. int16 works, but I would rather have it take up less space.

Should I not have it as a numpy array and just store it as a regular python list?

This is the array (i'm only including the first few lines, if you want the entire array let me know)

array([[[ 218,  219,  223],
        [   0,    0,    0],
        [   2,    2,    2],
        [   1,    1,    1],
        [   0,    0,    0],
        [   0,    0,    0],
        [   0,    0,    0],
        [   0,    0,    0],
        [  -3,   -3,   -3],
        [  -1,   -1,   -1],
        [   0,    0,    0],
        [  -1,   -1,   -1],
        [   0,    0,    0]]], dtype=int16)

Answer 1

I tried

import numpy as np
a = np.array([[[ 218,  219,  223],
        [   0,    0,    0],
        [   2,    2,    2],
        [   1,    1,    1],
        [   0,    0,    0],
        [   0,    0,    0],
        [   0,    0,    0],
        [   0,    0,    0],
        [  -3,   -3,   -3],
        [  -1,   -1,   -1],
        [   0,    0,    0],
        [  -1,   -1,   -1],
        [   0,    0,    0]]], dtype=np.int16)
signs = a<0.astype(np.bool)
a=a.astype(np.uint8)

But found it is actually worse than the original(206 bytes) vs. 167 for signs and 167 for the uint8 array.
The boolean seems to be taking as much as the uint8 - after looking into it I found that packbits will finally get you somewhere -

signs2 = np.packbits(signs, axis=None)

although at 106 bytes for the packed bytes, the uint8+signs still loses out to the original int16. Those sizes are as reported by sys.getsizeof(); if you use len(x.tostring()) you will find 78 bytes for the original array, 39 for the unsigned 8bit array, 39 for the boolean signs, and 5 for the packed signs.