Simple and safe evaluator

[bvdp]

Aahz wrote:
> In article <f407c296-9e02-47a6-8f17-b32332fbfcaf at u12g2000prd.googlegroups.com>,
> Simon Forman  <sajmikins at gmail.com> wrote:
>> FWIW, I got around to implementing a function that checks if a string
>> is safe to evaluate (that it consists only of numbers, operators, and
>> "(" and ")").  Here it is. :)
> 
> What's safe about "10000000 ** 10000000"?

Guess it depends on your definition of safe. I think that in most cases 
folks looking for "safe" are concerned about a malicious interjection of 
a command like "rm *" ... your example hangs the system for a long time 
and eventually will error out when it runs out of memory, but (probably) 
doesn't cause data corruption.

It would be nice if in a future version of Python we could have a 
safe/limited eval() ... which would limit the resources.