How to use the exec statement

Alex Martelli aleax at aleax.it
Mon Oct 7 18:31:06 CEST 2002


JB wrote:
        ...
> Well, I could preprocess the string that is given to exec. I
> am thinking about introducing '<---' instead of '=' anyway.
> Then only assignments, function calls and function
> definitions would be allowed.

You'll have to do a lot of special-purpose checks to
ensure e.g. that I don't do
        raise('gotcha')
LOOKS LIKE a function call, but since 'raise' is a
keyword, it's actually a raise statement and it's going 
to raise a string-exception:-).

> But even so, I cannot catch every error. But I could use
> except without a name, couldn't I? like in

Yes (sigh).


> def f(x,y):
>    try:
>      return x/y
>    except:
>      print 'error'
> 
> Then if I split the string that is give to exec I can even
> tell in which line the error occured.
> Is this sensible?

Not really, but there's not much else you can do:-(.

You don't need to split the string - as part of the
traceback (which you can get inside the handler) you
get the line-number on which the exception was raised.


Alex




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