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Jul 4th, 2009

Calculate CRC32 checksums (like SFVs)

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So far i've got this and it returns something like:

-2087276233

Python Syntax (Toggle Plain Text)
import binascii
def getCRC(filename):
     filedata = open(filename).read()
     return binascii.crc32(filedata)
import binascii
def getCRC(filename):
     filedata = open(filename).read()
     return binascii.crc32(filedata)

Someone told me that I had to use struct.pack or struct.unpack to change it to hex values.

I am not sure which type to convert to and would like some explanation to understand fully instead of coding in blind.

The final result should show the same CRC32 value as if you packed the file in WinRAR, checked it with the numerous SFV-checkers or whatever.

A link just in case:
http://docs.python.org/library/struct.html

Thanks alot in advance!

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dezza

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Jul 5th, 2009

Re: Calculate CRC32 checksums (like SFVs)

Post your code! Check your variables are properly set signed/unsigned!

wildgoose

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Jul 5th, 2009

Re: Calculate CRC32 checksums (like SFVs)

Click to Expand / Collapse Quote originally posted by wildgoose ...

Post your code! Check your variables are properly set signed/unsigned!

python Syntax (Toggle Plain Text)
import binascii
def getCRC(filename):
     filedata = open(filename).read()
     return binascii.crc32(filedata)
import binascii
def getCRC(filename):
     filedata = open(filename).read()
     return binascii.crc32(filedata)

dezza

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Jul 8th, 2009

Re: Calculate CRC32 checksums (like SFVs)

You may want to try a binary file read.

vegaseat

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DaniWeb's Hypocrite

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Jul 8th, 2009

Re: Calculate CRC32 checksums (like SFVs)

Click to Expand / Collapse Quote originally posted by vegaseat ...

You may want to try a binary file read.

Can you define this method? I am not sure I understand what you mean.

dezza

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Jul 18th, 2009

Re: Calculate CRC32 checksums (like SFVs)

http://dev.jmoiron.net/code/html/cksum.py.html

Can I use this code example to write a more simple approach?

I would prefer it in a single function, but the classes and etc. confuses me, I think he should simplify his code, it also gives a deprecation warning ..

dezza

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Jul 23rd, 2009

Re: Calculate CRC32 checksums (like SFVs)

I instead used a crc32.c script for use with subprocess .. Faster, and easier ..

dezza

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Jul 23rd, 2009

Re: Calculate CRC32 checksums (like SFVs)

Click to Expand / Collapse Quote originally posted by dezza ...

Can you define this method? I am not sure I understand what you mean.

Binary read is simply opening the file under the mode 'read' plus 'binary'. Read up on the built-in open method here, and the answer will reveal itself.

jlm699

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Jul 24th, 2009

Re: Calculate CRC32 checksums (like SFVs)

I have tried both open(filename, 'r') and open(filename, 'rb')

I can get the file loaded into a string and then try
print binascii.crc32(file-in-string)

Still just gives me negative integers, what I want is the 8-char hexvalue.

dezza

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Jul 25th, 2009

Re: Calculate CRC32 checksums (like SFVs)

Click to Expand / Collapse Quote originally posted by dezza ...

I have tried both open(filename, 'r') and open(filename, 'rb')

I can get the file loaded into a string and then try
print binascii.crc32(file-in-string)

Still just gives me negative integers, what I want is the 8-char hexvalue.

Use 'rb', and RTFM

Use string formatting to print the hex value, just as the example in the docs shows you.

jlm699

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