binary i/o

#!/usr/bin/python3
import sys
if len(sys.argv) != 4: sys.ext(1)
record_size = 30000
data_size = int(sys.argv[2])
if record_size < data_size: sys.exit(1)
with open(sys.argv[1], 'rb') as f:
    with open(sys.argv[3], 'wb') as w:
        data = f.read(record_size)
        while data:
            w.write(data[:data_size])
            data = f.read(record_size)