Reading And Interpreting Data From A Binary File In Python

I want to read a file byte by byte and check if the last bit of each byte is set: #!/usr/bin/python def main(): fh = open('/tmp/test.txt', 'rb') try: byte = fh.rea

Solution 1:

Try using the bytearray type (Python 2.6 and later), it's much better suited to dealing with byte data. Your try block would be just:

ba = bytearray(fh.read())
for byte in ba:
    print byte & 1

or to create a list of results:

low_bit_list = [byte & 1 for byte in bytearray(fh.read())]

This works because when you index a bytearray you 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 ord to convert it to an integer.

---

If your file is too big to comfortably hold in memory (though I'm guessing it isn't) then an mmap could be used to create the bytearray from a buffer:

import mmap
m = mmap.mmap(fh.fileno(), 0, access=mmap.ACCESS_READ)
ba = bytearray(m)

Solution 2:

You want to use ord instead of int:

if (ord(byte) & 0x01) == 0x01:

Solution 3:

One way:

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:

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()