va = bytes(1) # va: '\x00'
vb = bytes(2) # vb: '\x00\x00'
vc = bytes(5) # vc: '\x00\x00\x00\x00\x00'

vaa = struct.pack('>I', 1255) # vaa: '\x00\x00\x04\xe7'
vab = struct.pack('>II', 1255, 23) # vab: '\x00\x00\x04\xe7\x00\x00\x00\x17'
vaaa = struct.unpack('>I', vaa) # vaaa: <class 'tuple'>: (1255, )
vaba = struct.unpack('>II', vab) # vaba: <class 'tuple'>: (1255, 23)

import struct
from ctypes import create_string_buffer

# 創(chuàng)建一個9字節(jié)大小的緩存區(qū)，初始化默認全部為\x00 
buf = create_string_buffer(9) # buf.raw: '\x00\x00\x00\x00\x00\x00\x00\x00\x00'

# 沖緩存區(qū)buf的第0個字節(jié)開始打包兩個4字節(jié)無符號整型數(shù)據(jù)1和2
struct.pack_into(">II", buf, 0, 1, 2) # buf.raw: '\x00\x00\x00\x01\x00\x00\x00\x02\x00'
# 然后我們想再打包一個布爾型數(shù)據(jù)到buf中就可以改變以下偏移量
struct.pack_into(">?", buf, 8, True) # buf.raw: '\x00\x00\x00\x01\x00\x00\x00\x02\x01'

import struct
from ctypes import create_string_buffer

buf = create_string_buffer(9)
struct.pack_into(">II", buf, 0, 1, 2)
struct.pack_into(">?", buf, 8, True)
# 記錄位置
pos = 0
# 從buf緩存區(qū)中以大端方式從偏移位置pos處解包兩個無符號整型數(shù)據(jù)返回，注意
#返回值如果只寫一個則返回一個元組，否則你解包幾個數(shù)據(jù)就要寫幾個返回值。
val = struct.unpack_from('>II', buf, pos) # val: <class 'tuple'>: (1, 2)
val_a, val_b = struct.unpack_from('>II', buf, pos) # val_a: 1 val_b: 2

# 重置解包位置
pos += struct.calcsize('>II') # pos: 8
val_c, = struct.unpack_from('>?', buf, pos) # val_c: True

import struct
import os
import numpy as np
from ctypes import create_string_buffer
import cv2

# 創(chuàng)建一個60000 * 784 * 1 + 3 * 4字節(jié)大小的緩存區(qū)，初始化默認全部為\x00
buffer = create_string_buffer(60000 * 784 * 1 + 3 * 4)
def writeBytesData():
 index = 0
 BMP_NUM = 0
 BMP_WIDTH = 28
 BMP_HEIGHT = 28

 # 先保留三個無符號整型的緩存區(qū)
 index += struct.calcsize('>III')
 path = 'data/bmp'
 if not os.path.exists(path):
  print('No this dir!')
  return
 list = os.listdir(path)
 for line_bmp in list:
  bmp_path = os.path.join(path, line_bmp)
  if os.path.isdir(bmp_path):
   print('This is not a .bmp')
  else:
   BMP_NUM += 1
   print(BMP_NUM)
   buf = cv2.imread(bmp_path, cv2.IMREAD_GRAYSCALE)
   buf = np.reshape(buf, [784])
   for pos in range(buf.__len__()):
    struct.pack_into('>B', buffer, index, buf[pos])
    index += struct.calcsize('>B')

 # 將保留緩存區(qū)的內容填上
 struct.pack_into('>III', buffer, 0, BMP_NUM, BMP_WIDTH, BMP_HEIGHT)
 with open('data/bytes/bytes.bytes', 'wb') as fp:
  fp.write(buffer)


def readFromBytes():
 index = 0
 images = []
 with open('data/bytes/bytes.bytes', 'rb') as fp:
  buffer = fp.read()
  # 解包前三個無符號整型
  bmp_num, bmp_width, bmp_height = struct.unpack_from('>III', buffer, index)

  # 重定位偏移量
  index += struct.calcsize('>III')
  for pos in range(bmp_num):
   img = struct.unpack_from('>784B', buffer, index)
   index += struct.calcsize('>784B')
   # 修改為原來的圖片形狀
   img = np.array(img, dtype=np.uint8)
   img = np.reshape(img, [bmp_height, bmp_width])
   # 顯示圖片
   cv2.imshow('bmp', img)
   # 按任意鍵繼續(xù)
   cv2.waitKey(0)
   images.append(img)
 return images


writeBytesData()
readFromBytes()

bytes.py
data
 bmp
  1.bmp
  2.bmp
  ...
  60000.bmp
 bytes