Re: [Tutor] How to create memory backed file?

2009-12-27 Thread Modulok 
Kent,

Thanks! I think that'll do it. I don't know what this list would do without you!

-Modulok-

On 12/27/09, Kent Johnson  wrote:
> On Sun, Dec 27, 2009 at 3:36 AM, Modulok  wrote:
>> List,
>>
>> How do I create a file which exists only in memory? (Think diskless.)
>>
>> I need to create an in-memory file. I need to pass this file, as a
>> regular file object, to a subprocess. Unfortunately, the 'mmap'
>> module's file-like object doesn't appear to work quite like a regular
>> file would. (I simply assume that mmap would be the way to go. Other
>> suggestions welcome!) That, or I'm doing something terribly wrong.
>
> How about using a pipe for stdin? This seems to work:
>
> import sys
> from subprocess import Popen, PIPE
>
> fishes = "one fish\ntwo fish\nred fish\nblue fish\n"
>
> proc1 = Popen(['cat'], stdin=PIPE, stdout=sys.stdout, stderr=sys.stderr)
> proc1.stdin.write(fishes)
> proc1.stdin.close()
>
> Kent
>
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Re: [Tutor] How to create memory backed file?

2009-12-27 Thread Kent Johnson 
On Sun, Dec 27, 2009 at 3:36 AM, Modulok  wrote:
> List,
>
> How do I create a file which exists only in memory? (Think diskless.)
>
> I need to create an in-memory file. I need to pass this file, as a
> regular file object, to a subprocess. Unfortunately, the 'mmap'
> module's file-like object doesn't appear to work quite like a regular
> file would. (I simply assume that mmap would be the way to go. Other
> suggestions welcome!) That, or I'm doing something terribly wrong.

How about using a pipe for stdin? This seems to work:

import sys
from subprocess import Popen, PIPE

fishes = "one fish\ntwo fish\nred fish\nblue fish\n"

proc1 = Popen(['cat'], stdin=PIPE, stdout=sys.stdout, stderr=sys.stderr)
proc1.stdin.write(fishes)
proc1.stdin.close()

Kent
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Re: [Tutor] How to create memory backed file?

2009-12-27 Thread Emile van Sebille 

On 12/27/2009 12:03 PM Alan Gauld said...


"Modulok"  wrote


How do I create a file which exists only in memory? (Think diskless.)


The nearest I can think of is probably StringIO

Take a look at the docs for that and see if it works for you...



There's also http://docs.python.org/library/mmap.html -- but I've never 
tried it.


Emile


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Re: [Tutor] How to create memory backed file?

2009-12-27 Thread Alan Gauld 


"Modulok"  wrote


How do I create a file which exists only in memory? (Think diskless.)


The nearest I can think of is probably StringIO

Take a look at the docs for that and see if it works for you...

Alan G.

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[Tutor] How to create memory backed file?

2009-12-27 Thread Modulok 
List,

How do I create a file which exists only in memory? (Think diskless.)

I need to create an in-memory file. I need to pass this file, as a
regular file object, to a subprocess. Unfortunately, the 'mmap'
module's file-like object doesn't appear to work quite like a regular
file would. (I simply assume that mmap would be the way to go. Other
suggestions welcome!) That, or I'm doing something terribly wrong. For
example:

import mmap
import sys
from subprocess import Popen, PIPE

fishes = "one fish\ntwo fish\nred fish\nblue fish\n"

###
# With a real file, this works:
###
fd = open('fish.txt', 'w')
fd.write(fishes)
fd = open('fish.txt', 'r')
proc1 = Popen(['cat'], stdin=fd, stdout=sys.stdout, stderr=sys.stderr)

###
# This doesn't (with mmap file):
###
vfd = mmap.mmap(-1, len(fishes), mmap.MAP_PRIVATE)
vfd.write(fishes)
vfd.seek(0)
proc2 = Popen(['cat'], stdin=vfd.fileno(), stdout=sys.stdout, stderr=sys.stderr)

I just get the following error:

Traceback (most recent call last):
  File "", line 1, in 
AttributeError: fileno


I'm using Python 2.5, so I cannot use that slick
'SpooledTemporaryFile' method of the 'tempfile' module. The 'cat' is
just a simple Unix system command for the purpose of illustration.

Thanks!
-Modulok-
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