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So I am looking at code that I wrote perhaps as much as 4 years ago, and I know it ran correctly at the time. But now I am trying to run it, on a different computer than when I wrote it years ago and I am getting an error now. (Tried it today on both Windows 10 and Ubuntu)

I am using Python 2.7, as I was then too. I am using the Struct library to unpack C types from files, specifically I am trying to unpack 4 byte long values. Here is the documentation for the 2.7 struct library. https://docs.python.org/2/library/struct.html

If you scroll down to the "Format Characters" section, you can see a table of the C types.

Here is my code:

bps = int(unpack('L', fmap[o+10:o+14])[0])

And here is the error I get.

error: unpack requires a string argument of length 8

The part that is confusing me is the "length 8" part. If I change the C type to "I" the code executes fine. But the documentation seems clear that "L" is 4 byte as well, and it worked in the past. I think I can use the "I" type for my purposes, but I am curious if any one else has seen this.

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The standard size of L is 4 bytes, but that is only used if you are explicit about the endianness to use by beginning the format string with >, <, !, or =. Otherwise, the platform-dependent native size for your machine is used. (In this case, 8 bytes.)

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Ah, very interesting. I just tested it by adding '<' in front of the 'L' and it worked, so thank you very much. When I wrote and tested this years ago it would have been on a Windows XP system, so this makes a lot of sense.

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