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Nested Scopes Question (exec)

Rainer Deyke root at rainerdeyke.com
Sun Jun 24 21:05:03 EDT 2001 
"Rainer Deyke" <root at rainerdeyke.com> wrote in message
news:DWvZ6.362805$oc7.43089434 at news2.rdc2.tx.home.com...
> The wording here should probably be changed to "may or may not".
Otherwise
> people might start to rely on the fact that dictionary usually doesn't
> affect the local variables and do stuff like this:
>
> def f(x):
>   d = locals()
>   d['x'] += 5
>   exec 'print x' in d

Oops, bad example.  How about this:

def f(x):
  d = locals()
  d['x'] += 5
  assert d['x'] != x

I know, it's totally contrived.  More realistically:

def run_arbitrary_code(code):
  try:
    exec code in locals()
  except:
    print 'Exception raised by arbitrary code: "%s"' % code

run_arbitrary_code('del code;raise SyntaxError')


If modifying the dictionary returned from 'locals' changes the local
variables, then the function 'run_arbitrary_code' can be forced to throw an
exception by malicious code.


--
Rainer Deyke (root at rainerdeyke.com)
Shareware computer games           -           http://rainerdeyke.com
"In ihren Reihen zu stehen heisst unter Feinden zu kaempfen" - Abigor
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