CRC32 on files

[Adonis Vargas]

how do i run a CRC32 checksum on a file with python? or do i have the
concept all wrong.
pardon my ignorance, first time i even touch upon this subject.

thanks in advance.

Adonis

[Alex Martelli]

"Adonis Vargas" <delt...@telocity.com> wrote in message
news:3c355398$1...@nopics.sjc...

> how do i run a CRC32 checksum on a file with python? or do i have the

For example:

def crc32_of_file(filepath):
from zlib import crc32
fileobj = open(filepath,'rb')
current = 0
while 1:
buffer = fileobj.read(8192)
if not buffer: break
current = crc32(buffer, current)
fileobj.close()
return current

or, if you know the file ain't TOO huge, and are willing to trust
"automatic closure" of the opened file (explicit close is better...):

import zlib
thevalueyouwant = zlib.crc32(open(filepath,'rb').read())

Alex

[Nikolai Kirsebom]

Script I'm using to generate CRC on set of files:

#
# Generate CRC32 on file
#

import zlib
import array
import sys
import os

if __name__ == '__main__':
if len(sys.argv) < 2:
print "Usage: python GenCrc.py filename filename ..."
for fn in sys.argv[1:]:
fileSize = os.stat(fn)[6]
f = open(fn, "rb")
v = array.array('B')
try:
v.fromfile(f, fileSize)
i = zlib.crc32(v.tostring())
print "Crc32 of %s is :%d:" % (fn, i)
except:
print "Not able to read / generate CRC for file :%s:" %
(fn)

Nikolai

[Pete Shinners]

Adonis Vargas wrote:

hmm, you can use the SHA module to get a "SHA" checksum for a file. it
is a bit more intensive but also probably more 'unique' then crc.

import sha
def get_sha_checksum(filename):
filedata = open(filename).read()
return sha.new(filedata).hexdigest()

this will return a 40byte string of hex data. it also appears you can
get a straight up CRC32 checksum as well...

import binascii
def get_crc_checksum(filename):
filedata = open(filename).read()
return binascii.crc32(filedata)

that should do you pretty good. goodluck

[Laurent Szyster]

Alex Martelli wrote:
>
> or, if you know the file ain't TOO huge, and are willing to trust
> "automatic closure" of the opened file (explicit close is better...):

why?

Laurent