Python struct模块详解：字节序、打包与解包实战

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

# 创建一个9字节大小的缓存区，初始化默认全部为\x00 
buf = create_string_buffer(9) # buf.raw: '\x00\x00\x00\x00\x00\x00\x00\x00\x00'

# 冲缓存区buf的第0个字节开始打包两个4字节无符号整型数据1和2
struct.pack_into(">II", buf, 0, 1, 2) # buf.raw: '\x00\x00\x00\x01\x00\x00\x00\x02\x00'
# 然后我们想再打包一个布尔型数据到buf中就可以改变以下偏移量
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)
# 记录位置
pos = 0
# 从buf缓存区中以大端方式从偏移位置pos处解包两个无符号整型数据返回，注意
#返回值如果只写一个则返回一个元组，否则你解包几个数据就要写几个返回值。
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

# 创建一个60000 * 784 * 1 + 3 * 4字节大小的缓存区，初始化默认全部为\x00
buffer = create_string_buffer(60000 * 784 * 1 + 3 * 4)
def writeBytesData():
 index = 0
 BMP_NUM = 0
 BMP_WIDTH = 28
 BMP_HEIGHT = 28

 # 先保留三个无符号整型的缓存区
 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')

 # 将保留缓存区的内容填上
 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()
  # 解包前三个无符号整型
  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')
   # 修改为原来的图片形状
   img = np.array(img, dtype=np.uint8)
   img = np.reshape(img, [bmp_height, bmp_width])
   # 显示图片
   cv2.imshow('bmp', img)
   # 按任意键继续
   cv2.waitKey(0)
   images.append(img)
 return images


writeBytesData()
readFromBytes()

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