This is a very simple module for accessing platform-
specific entropy sources.  

On Win32, it uses CryptGenRandom.  Otherwise, it tries 
to use /dev/urandom.  If it can't find that, it raises 
NotImplementedError.

>>> import entropy
>>> entropy.entropy(10)
'\x99/\xbd\x8e\xb0\xfbz/\xf6\xe9'

To compile for Win32, you have to link with "advapi32".  
The /dev/urandom code has not been tested.

Issues:

 - I believe this works with all versions of Windows later 
than Win95.  But I'm not sure.

 - there's overhead in opening/closing the source.  On 
Win32 at least, opening it is slower than reading from it -
 it seems to take around 1/5th of a millisecond (i.e. I 
can make 5000 calls per second).  I think this is okay; 
you can make fewer calls and buffer the results, or seed 
your own PRNG.  However, we could make it more 
object-based, where you open an entropy-source, and 
then repeatedly read from it.

 - It would be nice if there was some attribute that told 
you what source you were using, so you could display 
it, and in case you trust /dev/urandom but not Win32's 
CryptoAPI, for example.