如何在文件中查找字节序列？

Question

我有一个 二进制 文件，我需要在其中更改某些位。

该位的字节地址是相对于某个字节序列（某个 ASCII 字符串）的：

content = array('B')
with open(filename, mode="r+b") as file:
    content.fromfile(file, os.fstat(file.fileno()).st_size)
    abc = [ord(letter) for letter in "ABC"]
    i = content.index(abc) // ValueError: array.index(x): x not in list
    content[i + 0x16] |= 1
    content.tofile(file)

但是我必须承认我的耻辱，在谷歌搜索之后，我找不到获取“ABC”字符串索引的方法......

当然，我可以编写一个使用循环执行此操作的函数，但我不敢相信没有单行（好吧，甚至两个...）可以完成它。

怎么做？

Answer 1

不确定这是否是最 Pythonic 的方式，但这是可行的。在这个文件中

$ cat so.bin    
���ABC̻�X��w
$ hexdump so.bin
0000000 eeff 41dd 4342 bbcc 58aa 8899 0a77     
000000e

编辑：新的解决方案从这里开始。

import string

char_ints = [ord(c) for c in string.ascii_letters]

with open("so.out.bin", "wb") as fo:
    with open("so.bin", "rb") as fi:

        # Read bytes but only keep letters.
        chars = []
        for b in fi.read():
            if b in char_ints:
                chars.append(chr(b))
            else:
                chars.append(" ")

        # Search for 'ABC' in the read letters.
        pos = "".join(chars).index("ABC")

        # We now know the position of the intersting byte.
        pos_x = pos + len("ABC") + 3 # known offset

        # Now copy all bytes from the input to the output, ...
        fi.seek(0)
        i = 0
        for b in fi.read():
            # ... but replace the intersting byte.
            if i == pos_x:
                fo.write(b"Y")
            else:
                fo.write(bytes([b]))
            i = i + 1

编辑：新的解决方案到此结束。

我想在ABC 之后获得X 四个位置。一点点状态保持定位ABC的位置，跳过偏移量，打印感兴趣的字节。

foundA = False
foundB = False
foundC = False
found = False
offsetAfterC = 3
lengthAfterC = 1

with open("so.bin", "rb") as f:
    pos = 0
    for b in f.read():
        pos = pos + 1
        if not found:
            if b == 0x41:
                foundA = True
            elif foundA and b == 0x42:
                foundB = True
            elif foundA and foundB and b == 0x43:
                foundC = True
            else:
                foundA, foundB, foundC = False, False, False

        if foundA and foundB and foundC:
            found = True
            break

    f.seek(0)
    i = 0
    while i < pos + offsetAfterC:
        b = f.read(1)
        i = i + 1
    while i < pos + offsetAfterC + lengthAfterC:
        b = f.read(1)
        print(hex(int.from_bytes(b, byteorder="big")))
        i = i + 1

输出：

0x58