Spoiler to Python Challenge (help!!!)

Terry Hancock hancock at anansispaceworks.com
Tue Sep 27 17:42:20 CEST 2005


On Tuesday 27 September 2005 08:32 am, Ian Vincent wrote:
> I have a webpage with a BZ2 compressed text embedded in it looking like:
> 
> 'BZh91AY&SYA\xaf\x82\r\x00\x00\x01\x01\x80\x02\xc0\x02\x00 \x00!\x9ah3M
> \x07<]\xc9\x14\xe1BA\x06\xbe\x084'
> 
> Now, if I simply copy and paste this into Python and decompress it - it 
> works a treat.
> 
> However, I want to read the file containing this data, extract the data 
> and decompress it and this for some reason does not work.
> [...]
> This gives me a user string of:
> 
> BZh91AY&SYA\xaf\x82\r\x00\x00\x01\x01\x80\x02\xc0\x02\x00 \x00!\x9ah3M
> \x07<]\xc9\x14\xe1BA\x06\xbe\x084
> 
> But if I put this into the decompression function, I get a error of 
> 'IOError: invalid data stream'.
> 
> I know it is the escape characters but how do I get these to be correctly 
> converted into a string compatible with bz2.decompress()?

Took me a long time to figure out what you meant. ;-)

So the string actually contains the backslashes, not the escaped characters.

This works:

>>> bz2.decompress(eval(repr(user)))
'huge'

(which I take it is what your sample data encoded -- though I can't help
but notice it is actually much shorter than the "compressed" version. ;-)).

This may have some security issues, though, since it evaluates essentially
any expression given for user.  I'd be interested to know if someone
knows a more secure way.

Cheers,
Terry

--
Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com




More information about the Python-list mailing list