在 Python 中读取和解释二进制文件中的数据
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Reading and interpreting data from a binary file in Python
提问by dubbaluga
I want to read a file byte by byte and check if the last bit of each byte is set:
我想逐字节读取文件并检查是否设置了每个字节的最后一位：
#!/usr/bin/python
def main():
fh = open('/tmp/test.txt', 'rb')
try:
byte = fh.read(1)
while byte != "":
if (int(byte,16) & 0x01) is 0x01:
print 1
else:
print 0
byte = fh.read(1)
finally:
fh.close
fh.close()
if __name__ == "__main__":
main()
The error I get is:
我得到的错误是：
Traceback (most recent call last):
File "./mini_01.py", line 21, in <module>
main()
File "./mini_01.py", line 10, in main
if (int(byte,16) & 0x01) is 0x01:
ValueError: invalid literal for int() with base 16: '\xaf'
Anyone an idea? I didn't succeed using the struct and the binascii modules.
任何人的想法？我没有成功使用 struct 和 binascii 模块。
采纳答案by nmichaels
You want to use ordinstead of int:
你想使用ord而不是int：
if (ord(byte) & 0x01) == 0x01:
回答by Scott Griffiths
Try using the bytearraytype (Python 2.6 and later), it's much better suited to dealing with byte data. Your tryblock would be just:
尝试使用bytearray类型（Python 2.6 及更高版本），它更适合处理字节数据。您的try块将只是：
ba = bytearray(fh.read())
for byte in ba:
print byte & 1
or to create a list of results:
或创建结果列表：
low_bit_list = [byte & 1 for byte in bytearray(fh.read())]
This works because when you index a bytearrayyou just get back an integer (0-255), whereas if you just read a byte from the file you get back a single character string and so need to use ordto convert it to an integer.
这是有效的，因为当您索引 a 时，bytearray您只会返回一个整数（0-255），而如果您只是从文件中读取一个字节，则会返回一个单个字符串，因此需要使用ord将其转换为整数。
If your file is too big to comfortably hold in memory (though I'm guessing it isn't) then an mmapcould be used to create the bytearrayfrom a buffer:
如果您的文件太大而无法舒适地保存在内存中（尽管我猜它不是）那么mmap可以使用an来bytearray从缓冲区创建：
import mmap
m = mmap.mmap(fh.fileno(), 0, access=mmap.ACCESS_READ)
ba = bytearray(m)
回答by tzot
One way:
单程：
import array
filebytes= array.array('B')
filebytes.fromfile(open("/tmp/test.txt", "rb"))
if all(i & 1 for i in filebytes):
# all file bytes are odd
Another way:
其它的办法：
fobj= open("/tmp/test.txt", "rb")
try:
import functools
except ImportError:
bytereader= lambda: fobj.read(1)
else:
bytereader= functools.partial(fobj.read, 1)
if all(ord(byte) & 1 for byte in iter(bytereader, '')):
# all bytes are odd
fobj.close()
