将Little-endian 24位文件转换为ASCII数组

Question

我有一个.raw文件，其中包含52行html标头，其后是数据本身。 该文件以Little-endian 24bits SIGNED编码，我想将数据转换为ASCII文件中的整数。 我使用Python 3 。

我试图用在这篇文章中找到的以下代码来“解压缩”整个文件：

import sys
import chunk
import struct

f1 = open('/Users/anais/Documents/CR_lab/Lab_files/labtest.raw', mode = 'rb')
data = struct.unpack('<i', chunk + ('\0' if chunk[2] < 128 else '\xff'))   

但我收到此错误消息：

TypeError: 'module' object is not subscriptable

编辑

看来这更好：

data = struct.unpack('<i','\0'+ bytes)[0] >> 8

但是我仍然收到错误消息：

TypeError: must be str, not type

我想容易修复吗？

Answer 1

那不是在Python中处理的好文件！ Python非常适合处理文本文件，因为它会在内部缓冲区中大块读取它们，然后在行上进行迭代，但是您无法轻易访问像这样读取文本后出现的二进制数据。 此外， struct模块不支持24位值。

我能想象的唯一方法是一次读取一个字节的文件，首先在行尾跳过52次，然后一次读取3个字节，将它们连接成4个字节的字节字符串，然后解压缩。

可能的代码可能是：

eol = b'\n'          # or whatever is the end of line in your file
nlines = 52          # number of lines to skip

with open('/Users/anais/Documents/CR_lab/Lab_files/labtest.raw', mode = 'rb') as f1:

    for i in range(nlines):       # process nlines lines
        t = b''                   # to store the content of each line
        while True:
            x = f1.read(1)        # one byte at a time
            if x == eol:          # ok we have one full line
                break
            else:
                t += x            # else concatenate into current line
        print(t)                  # to control the initial 52 lines

    while True:
        t = bytes((0,))               # struct only knows how to process 4 bytes int
        for i in range(3):            # so build one starting with a null byte
            t += f1.read(1)
        # print(t)
        if(len(t) == 1): break        # reached end of file
        if(len(t) < 4):               # reached end of file with uncomplete value
            print("Remaining bytes at end of file", t)
            break
        # the trick is that the integer division by 256 skips the initial 0 byte and keeps the sign
        i = struct.unpack('<i', t)[0]//256   # // for Python 3, only / for Python 2
        print(i, hex(i))                     # or any other more useful processing

备注：上面的代码假定您对52行的描述（以行尾终止）是正确的，但是显示的图像让我们认为最后一行不是。 在这种情况下，您应该首先计数51行，然后跳过最后一行的内容。

def skipline(fd, nlines, eol):
    for i in range(nlines):       # process nlines lines
        t = b''                   # to store the content of each line
        while True:
            x = fd.read(1)        # one byte at a time
            if x == eol:          # ok we have one full line
                break
            else:
                t += x            # else concatenate into current line
        # print(t)                  # to control the initial 52 lines

with open('/Users/anais/Documents/CR_lab/Lab_files/labtest.raw', mode = 'rb') as f1:
    skiplines(f1, 51, b'\n')     # skip 51 lines terminated with a \n
    skiplines(f1, 1, b'>')       # skip last line assuming it ends at the >

    ...