Creating random binary files

Question

I\'m trying to use python to create a random binary file. This is what I\'ve got already:

f = open(filename,\'wb\')
for i in xrange(size_kb):
    for ii in xrang         


        

Answer 1

The python code you should write completely depends on the way you intend to use the random binary file. If you just need a "rather good" randomness for multiple purposes, then the code of Jon Clements is probably the best.

However, on Linux OS at least, os.urandom relies on /dev/urandom, which is described in the Linux Kernel (drivers/char/random.c) as follows:

The /dev/urandom device [...] will return as many bytes as are requested. As more and more random bytes are requested without giving time for the entropy pool to recharge, this will result in random numbers that are merely cryptographically strong. For many applications, however, this is acceptable.

So the question is, is this acceptable for your application ? If you prefer a more secure RNG, you could read bytes on /dev/random instead. The main inconvenient of this device: it can block indefinitely if the Linux kernel is not able to gather enough entropy. There are also other cryptographically secure RNGs like EGD.

Alternatively, if your main concern is execution speed and if you just need some "light-randomness" for a Monte-Carlo method (i.e unpredictability doesn't matter, uniform distribution does), you could consider generate your random binary file once and use it many times, at least for development.

Answer 2

IMHO - the following is completely redundant:

f.write(struct.pack("=I",random.randint(0,sys.maxint*2+1)))

There's absolutely no need to use struct.pack, just do something like:

import os

with open('output_file', 'wb') as fout:
    fout.write(os.urandom(1024)) # replace 1024 with size_kb if not unreasonably large

Then, if you need to re-use the file for reading integers, then struct.unpack then.

(my use case is generating a file for a unit test so I just need a file that isn't identical with other generated files).

Another option is to just write a UUID4 to the file, but since I don't know the exact use case, I'm not sure that's viable.