xlrd: struct.error: unpack requires a string argument of length 512

If you have an xls file that opens OK in Excel, OpenOffice Calc, or Gnumeric, but isn't opened by xlrd, then you should e-mail the xlrd author (sjmachin at lexicon dot net) with the details and a copy of the file, so that xlrd can be improved; this will benefit you and all other xlrd users.

Update after examining the source:

The stack trace that you supplied was from the antique 0.6.1 version; why on earth are you using that?

According to my reading of the code, xlrd should have emitted a message like this: `WARNING * file size (SIZE) not 512 + multiple of sector size (512)' ... did it?

This is already out of spec. Often the cause is that the data payload (the Workbook stream) is not a multiple of 512 bytes, it is the last structure written, and the writer has not bothered to pad it out. In that case it is safe to continue, as the missing padding will not be accessed.

However, in your case where xlrd falls off the end of the file it is following a chain of index sectors (MS calls it the "double indirect FAT") that is used when the file size is bigger than about 7 MB. The last 4 bytes in each of those sectors contains the sector number of the next sector in the chain (or a special end-of-chain value). Consequently if one of those sectors is shorter than 512 bytes, the file is corrupt. Recovering from that without even a warning message is NOT something that I'd call good behaviour, and NOT something I'd be advocating SO users to rely on.

Please contact me via e-mail to discuss how I can get a copy of this file (under a non-disclosure agreement, if necessary).