src_fname = '/bin/cat'
dst_fname = '/tmp/cat.bak2'
src_fobj = open(src_fname, 'rb')
dst_fobj = open(dst_fname, 'wb')
while 1:
    data = src_fobj.read(4096)
    if  not data:
        break
    dst_fobj.write(data)
src_fobj.close()
dst_fobj.close()