Hi All-- John Machin wrote: > > On Sun, 17 Apr 2005 22:06:04 -0600, Ivan Van Laningham > <[EMAIL PROTECTED]> wrote: > [snip] > > So I wrote a set of > >programs to both index the disk versions with the cd versions, and to > >compare, using filecmp.cmp(), the cd and disk version. Works fine. > >Turned up several dozen files that had been inadvertantly rotated or > >saved with the wrong quality, various fat-fingered mistakes like that. > > > >However, it didn't flag the files that I know have bitrot. I seem to > >remember that diff uses a checksum algorithm on binary files, not a > >byte-by-byte comparison. Am I wrong? > > According to the docs: > > """ > cmp( f1, f2[, shallow[, use_statcache]]) > > Compare the files named f1 and f2, returning True if they seem equal, > False otherwise. > Unless shallow is given and is false, files with identical os.stat() > signatures are taken to be equal > """ > > and what is an os.stat() signature, you ask? So did I. > > According to the code itself: > > def _sig(st): > return (stat.S_IFMT(st.st_mode), > st.st_size, > st.st_mtime) > > Looks like it assumes two files are the same if they are of the same > type, same size, and same time-last-modified. Normally I guess that's > good enough, but maybe the phantom bit-toggler is bypassing the file > system somehow. What OS are you running? >
WinXP, SP2 > You might like to do two things: (1) run your comparison again with > shallow=False (2) submit a patch to the docs. > You know, I read that doc, tried it, and it made absolutely no difference. Then I read your message, read the docs again, and finally realized I had flipped the sense of shallow in my head. Sheesh. So then I tried it with shallow=False, not True, and it runs about ten times slower, but it works. Beautifully. Now I have to go back and redo the first five thousand, but it's worth it. Thanks. Shows how much you need another set of eyeballs to debug your brain;-) > (-: > You have of course attempted to eliminate other variables by checking > that the bit-rot effect is apparent using different display software, > a different computer, an observer who's not on the same medication as > you, ... haven't you? > :-) > ;-) Absolutely. Several different viewers and several different OSs. And my wife never sees anything the way I do;-) Metta, Ivan ---------------------------------------------- Ivan Van Laningham God N Locomotive Works http://www.andi-holmes.com/ http://www.foretec.com/python/workshops/1998-11/proceedings.html Army Signal Corps: Cu Chi, Class of '70 Author: Teach Yourself Python in 24 Hours -- http://mail.python.org/mailman/listinfo/python-list
