将 Little-endian 24 位文件转换为 ASCII 数组

Question

我有一个包含 52 行 html header 的 .raw 文件，后跟数据本身。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。我用 Python 3.

我尝试 'unpack' 整个文件，并在 this post 中找到以下代码：

import sys
import chunk
import struct

f1 = open('/Users/anais/Documents/CR_lab/Lab_files/labtest.raw', mode = 'rb')
data = struct.unpack('<i', chunk + ('[=11=]' if chunk[2] < 128 else '\xff'))

但我收到此错误消息：

TypeError: 'module' object is not subscriptable

编辑

好像这样更好:

data = struct.unpack('<i','[=13=]'+ bytes)[0] >> 8

但我仍然收到错误消息：

TypeError: must be str, not type

我想很容易修复？

Answer 1

在 Python 中处理这不是一个很好的文件！ Python 非常适合处理文本文件，因为它会在内部缓冲区中以大块的形式读取它们，然后逐行迭代，但是您无法轻松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。

我能想到的唯一方法是一次一个字节地读取文件，首先跳过 52 次行尾，然后一次读取 3 个字节，将它们连接成一个 4 字节的字节字符串并解压.

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：以上代码假定您对 52 行（以行尾结束）的描述是正确的，但显示的图像让我们认为最后一行不是。那样的话，你应该先算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 >

    ...

将 Little-endian 24 位文件转换为 ASCII 数组

Convert Little-endian 24 bits file to an ASCII array

python

io

binaryfiles

type-conversion

endianness