[Tutor] file object in memory

[Martin Walsh]

Monika Jisswel wrote:
> You know bob, you are very clever, I have used RAM disk for realtime
> recording of audio before but it never occured to me to use it for light
> jobs like this one, I just compeletely ignored it as an option & by the
> way this openes a lot of doors for many of my other programs.
> 
> but wouldn't it be very nice if there  was a way of creating a file
> object inside python ? something like :
> myfile = mkfile('some_string')
> & we're done ?

If I understand what you're after, perhaps tempfile.NamedTemporaryFile
is close. Granted it creates a 'real' file, subject to filesystem
performance, but it is automatically deleted when closed.

---

Also, while I wouldn't recommend it, I thought it might be worth
mentioning that you can specify a named pipe (or fifo) with mysql 'load
data' -- although this may be limited to *nix or Mac, I'm not sure.

It is a tricky dance since, IIUC, the mysql process has to open the
named pipe for reading before you can write to it, else the write will
block waiting for a reader and your program will hang. My first thought
would be to spawn a subprocess of the mysql client, or mysqlimport, to
start the read, then write data to the named pipe. Something like the
following (untested):

...

fifoname = '/tmp/mysql.fifo'
if os.path.exists(fifoname):
    os.remove(fifoname)
os.mkfifo(fifoname)

sql = """\
"load data local infile '%s' into table statistics
    fields terminated by '\\t' lines terminated by '\\n';"
""" % fifoname

conninfo[sql] = sql
mysqlcmd = \
  'mysql %(dbname)s -h %(host)s -u %(user)s -e %(sql)s' % conninfo

mysqlp = sp.Popen(mysqlcmd, stdout=sp.PIPE, shell=True)

# should be ready to write
fifofp = file(fifoname, 'w')
p1 = sp.Popen(somecmd1, stdout=fifofp, shell=True)
fifofp.close()

mysqlp.wait()

...

Seems like an awful lot of work, for questionable gain. I would use a
regular file. If you're concerned about performance, Bob's ramdisk
suggestion seems more appropriate.

HTH,
Marty

> 
> 
>     I don't think there is a pure Pythonic way. Have you considered
>     using a RamDisk? http://en.wikipedia.org/wiki/RAM_disk for general
>     details.
> 
>     http://www.codeguru.com/cpp/w-p/system/devicedriverdevelopment/article.php/c5789/
>     for a Windows Ram Disk driver installer. I just tried it - it works
>     like a charm.
> 
>     HTH.
> 
>     -- 
>     Bob Gailer
>     919-636-4239 Chapel Hill, NC