Maurice Ling <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > [EMAIL PROTECTED] wrote: > >>I have written a program to do something similar. My strategy is: >> * use os.read() to read 512 bytes at a time >> * when os.read fails, seek to the next multiple of 512 bytes >> and write '\0' * 512 to the output >>I notice this code doesn't deal properly with short reads, but in my >>experience >>they never happen (because the disk error makes an entire block >>unreadable, and >>a block is never less than 512 bytes) >> >>I use this code on a unix-style system. >> >>def dd(src, target, bs=512): >> src = os.open(src, os.O_RDONLY) >> if os.path.exists(target): >> target = os.open(target, os.O_WRONLY | os.O_APPEND, 0600) >> existing = os.lseek(target, 0, SEEK_END) >> else: >> existing = 0 >> target = os.open(target, os.O_WRONLY | os.O_CREAT, 0600) >> >> total = os.lseek(src, 0, SEEK_END) / bs >> os.lseek(src, existing, SEEK_SET) >> os.lseek(target, existing, SEEK_SET) >> >> if existing: print "starting at", existing >> i = existing / bs >> f = 0 >> lastrem = -1 >> >> last = start = time.time() >> while 1: >> try: >> block = os.read(src, bs) >> except os.error, detail: >> if detail.errno == errno.EIO: >> block = "\0" * bs >> os.lseek(src, (i+1) * bs, SEEK_SET) >> f = f + 1 >> else: >> raise >> if block == "": break >> >> i = i + 1 >> os.write(target, block) >> >> now = time.time() >> if i % 1000 or now - last < 1: continue >> last = now >> >> frac = i * 1. / total >> rem = int((now-start) * (1-frac) / frac) >> if rem < 60 or abs(rem - lastrem) > .5: >> rm, rs = divmod(rem, 60) >> lastrem = rem >> spd = i * 512. / (now - start) / 1024 / 1024 >> sys.stderr.write("%8d %8d %8d %3.1f%% %6d:%02d %6.1fMB/s\r" >> % (i, f, i-f, i * 100. / total, rm, rs, spd)) >> sys.stderr.write("\n") >> >> > Sorry but what are SEEK_END and SEEK_SET?
The Python 2.3 documentation seems to specify the *numeric* values of these constants only. But since Python's file objects are "implemented using C's stdio package", you can read http://www.opengroup.org/onlinepubs/009695399/functions/lseek.html Regards, Christian Stapfer -- http://mail.python.org/mailman/listinfo/python-list
