zlib and gzip

[Bakken, Gregory A]

Below is a very simple sample, but I think it illustrates the problem.  In
short, I have a text string in readable format, and compressed/encoded by
the other app.  My getString function below can recover the original string
from what is provided by the other app.  If I take the original string and
try to compress/encode and then recover it, both approaches I have tried
fail.  (In other words, the script below will actually crash with an error
something like zlib.error:  Error -3 while decompressing data: invalid block
type

import gzip, zlib, StringIO, base64

def getString(s):
    s = base64.decodestring(s)
    s = zlib.decompress(s, -15)
    return s

def makeString1(s):
    s = zlib.compress(s, 9)
    s = base64.encodestring(s)
    return s

def makeString2(s):
    sio = StringIO.StringIO()
    gzipper = gzip.GzipFile(mode="wb", fileobj=sio)
    gzipper.write(s)
    s = base64.encodestring(sio.getvalue())
    return s

previouslyMadeString = "81RIzFVIVChKTUxJTMpJVSguKcrMSwcA"
readableString = "I am a readable string"

print "Original string"
print readableString
print ""
print "Decoded string form other program"
print getString(previouslyMadeString)
print ""

ms1 = makeString1(readableString)
gs1 = getString(ms1)
print "Decoded from appraoch 1"
print gs1

ms2 = makeString2(readableString)
gs2 = getString(ms2)
print "Decoded from appraoch 1"
print gs2


-----Original Message-----
From: Hornberger, Chris [mailto:Chris.Hornberger at blackrock.com]
Sent: Wednesday, May 12, 2004 1:14 PM
To: Bakken, Gregory A; python-list at python.org
Subject: RE: zlib and gzip


Ok, fair enough. Can you supply (if it's non-sensitive information) some
samples? 

I'm on this conference call for the next hour or so, so I'm glued to my
desk. I have time to tinker. It's just a general status call. I just have to
chime in from time to time.

--------------------------
Chris Hornberger
Blackrock - 302.797.2318
chris.hornberger at blackrock.com

Card carrying MSDN member since 2004.
No, really. I've got the card to prove it.


-----Original Message-----
From: Bakken, Gregory A [mailto:gregory_a_bakken at groton.pfizer.com]
Sent: Wednesday, May 12, 2004 1:10 PM
To: Hornberger, Chris; python-list at python.org
Subject: RE: zlib and gzip


The short answer is I don't know.  The longer answer is that I really don't
know the driving force behind the compression/encoding that is being used.
What I am doing is a more downstream process (so I am stuck with the chosen
scheme).

-----Original Message-----
From: Hornberger, Chris [mailto:Chris.Hornberger at blackrock.com]
Sent: Wednesday, May 12, 2004 1:04 PM
To: Greg Bakken; python-list at python.org
Subject: RE: zlib and gzip


Silly questions first: Is it just a matter of 72 column-bounding to make it
email-compliant? (keep in mind I haven't  run your sample code yet, I'm
sitting here perusing while on a conference call - meetings suck!!!)

--------------------------
Chris Hornberger
Blackrock - 302.797.2318
chris.hornberger at blackrock.com

Card carrying MSDN member since 2004.
No, really. I've got the card to prove it.


-----Original Message-----
From: python-list-bounces+chris.hornberger=blackrock.com at python.org
[mailto:python-list-bounces+chris.hornberger=blackrock.com at python.org]On
Behalf Of Greg Bakken
Sent: Wednesday, May 12, 2004 12:57 PM
To: python-list at python.org
Subject: zlib and gzip


I am writing a python program that recieves 'compressed and encoded'
strings from another piece of software.  I can successfully uncompress
and decode the strings via

import base64, zlib
def getString(s):
  s = base64.decodestring(s)
  s = zlib.decompress(s, -15)
  return s

Now, I want to take a 'readable' text string, and compress and encode
it the same way as the other piece of software.  I first tried the
seemingly obvious (but incorrect)

import base64, zlib
def makeString(s):
  s = zlib.compress(s, 9)
  s = base64.encodestring(s)
  return s

I have also tried using the gzip module to do this like

import base64, gzip, StringIO
def makeString(s):
  sio = StringIO.StringIO()
  gzipper = gzip.GzipFile(mode="wb", fileobj=sio)
  gzipper.write(s)
  s = base64.encodestring(sio.getvalue())
  return s

What I would like to be able to do is take a string s, pass it through
the makeString function, and pass the result through the getString
function, and end up with the original string s back.  I have to stick
with the way getString is, so I can handle strings from another
program, so I need to adapt makeString accordingly, but cannot figure
out how.

Greg
-- 
http://mail.python.org/mailman/listinfo/python-list


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