On Nov 20, 3:14 pm, Grant Edwards <[EMAIL PROTECTED]> wrote: > On 2007-11-20, p. <[EMAIL PROTECTED]> wrote: > > > > >> By "memory" I presume you mean virtual memory? RAM with > >> disk-blocks as backing store? On any real OS, tempfiles are > >> just RAM with disk-blocks as backing store. > > >> Sound similar? The only difference is the API used to access > >> the bytes. You want a file-I/O API, so you can either use the > >> extensively tested and and highly optimized filesystem code in > >> the OS to make disk-backed-RAM look like a file, or you can try > >> to write Python code that does the same thing. > > >> Which do you think is going to work faster/better? > > >> [The kernel is generally better at knowing what needs to be in > >> RAM than you are -- let it do its job.] > > >> IOW: just use a temp file. Life will be simple. The bytes > >> probably won't ever hit the platters (if they do, then that > >> means they would have the other way too). > > > Grant, are temp files automatically put into ram for all linux > > distros? > > All files are put into ram for all linux distros that use > virtual memory. (You'll know if you're not using virtual.) > > > at any rate, i could set up ram disk. much better solution > > than using python...except that i've never done a ram disk > > before. more reading to do... > > You don't have set up a ram disk. You already have one. All > your disks are ram disks. It's just that some of them have > magnetic platters as backing store so they get preserved during > a reboot. On some Linux distros, the /tmp directory is a > filesystem without prmanent magnetic backing-store. On others > it does have a permanent backing store. If you do a "mount" > command, you'll probably see a "filesystem" who's type is > "tmpfs". That's a filesystem with no permanent magnetic > backing-store[1]. > > Seehttp://en.wikipedia.org/wiki/TMPFS > > /tmp might or might not be in a tmpfs filesystem (depends on > the distro). In any case, you probably don't need to worry > about it. > > Just call tempfile.NamedTemporaryFile() and tell it you want an > unbuffered file (that way you don't have to remember to flush > the file after writing to it). It will return a file object: > > f = tempfile.NamedTemporaryFile(bufsize=0) > > Write the data to that file object and flush it: > > f.write(mydata) > > Pass the file's name to whatever broken library it is that > insists on a file name instead of a file-like object: > > brokenLib.brokenModule(f.name). > > When you're done, delete the file object: > > del f > > NB: This particular approach won't work on Windows. On Windows > you'll have to use tempfile.mktemp(), which can have race > conditions. It returns a name, so you'll have to create > the file, write to it, and then pass the name to the broken > module. > > [1] Tmpfs pages use the swap partition for temporary backing > store the same as for all other memory pages. If you're > using tmpfs for big stuff, make sure your swap partition is > large enough to hold whatever you're doing in tmpfs plus > whatever normal swapping capacity you need. > > ------------------------------demo.py------------------------------ > def brokenModule(filename): > f = file(filename) > d = f.read() > print d > f.close() > > import tempfile,os > > f = tempfile.NamedTemporaryFile(bufsize=0) > n = f.name > print f,":",n > os.system("ls -l %s\n" % n) > > f.write("hello world") > brokenModule(n) > > del f > os.system("ls -l %s\n" % n) > ------------------------------demo.py------------------------------ > > If you run this you'll see something like this: > > $ python demo.py > <open file '<fdopen>', mode 'w+b' at 0xb7c37728> : /tmp/tmpgqSj8p > -rw------- 1 grante users 0 2007-11-20 17:11 /tmp/tmpgqSj8p > hello world > ls: cannot access /tmp/tmpgqSj8p: No such file or directory > > -- > Grant Edwards grante Yow! I want to mail a > at bronzed artichoke to > visi.com Nicaragua!
excellent. didn't know tempfile was a module. thanks so much. -- http://mail.python.org/mailman/listinfo/python-list
