[Tutor] The Evil eval()

[alan.gauld@bt.com]

> list of lists all on  one line.  Something like:
> 
> [[1, 2, 3, 4, 5], [2, 4, 6, 8, 10], [3, 6, 9, 12, 15], [4, 8, 
> 12, 16, 20]]
> 
> I will have to use eval().  

Thats the easy way to do it yes.

> know that is dangerous and if someone knew I used that for 
> this program, they could really mess things up.  

If they have access to edit the file certainly.

> My question is, how do I make sure that
> what I am eval()-ing is a list of lists (of integers)?  

The only way to be sure is to parse the entire file.
If you feel that is necessary I would actually consider 
moving the data format to XML and using the precanned 
parsers.

But is it really the case? Is there no way you can be 
confident that the data files will not be tampered with?

One other thing which is pretty secure but not bombproof 
would be to calculate a checksum for the file and store 
that somewhere. You can compare the checksum with the 
current files checksum to see if it has changed. 
Thats pretty solid but not absolutely 100%...

Alan G.