How to eval a file

[Alex Martelli]

Björn Lindberg wrote:
   ...
> I see now. BTW, isn't it a bit strange that the eval syntax is
> eval(<expr>), whereas exec is written without parantheses, exec
> "<statement>"?

No, because eval is a function while exec is a statement.

All functions are always called with parentheses.

Statements never _demand_ parentheses EXCEPT the 'def' statement
(which parallels function-call in this way) -- and 'class' if
it involves bases classes.

> Ah, I see now. I thought that by just doing "execfile(filename)", the
> variables would automagically appear in the local namespace. The

They do, and that is exactly why you should not use it that way:
you completely lose control of what's defined in your local namespace 
after that.  It makes errors likely and debugging far too hard.


> You are right. I was trying to take advantage of the fact that I am
> using a very high level language. But still, there are fewer security
> implications and more error checking by parsing it manually. I think I
> will use the execfile() solution for now, and when it gets closer to
> being finished, I will write a proper parser instead.

This is a reasonable compromise.  But make sure you use execfile
WITH an explicit namespace anyway -- even just to debug &c -- you'll
be glad you did.


Alex