safe eval of moderately simple math expressions

[Joel Hedlund]

Peter Otten wrote:
> But what you're planning to do seems more like
> 
>>>> def is_it_safe(source):
> ...     return "_" not in source
> ...
>>>> source = "getattr(42, '\\x5f\\x5fclass\\x5f\\x5f')"
>>>> if is_it_safe(source):
> ...     print eval(source)
> ...
> <type 'int'>

Bah. You are completely right of course.

Just as a thought experiment, would this do the trick?

def is_it_safe(source):
     return "_" not in source and r'\' not in source

I'm not asking because I'm hellbent on having eval in my app, but 
because it's always useful to see what hazards you don't know about.

/Joel