List comprehension - NameError: name '_[1]' is not defined ?

[Steven D'Aprano]

On Thu, 15 Jan 2009 03:29:59 -0800, mario ruggier wrote:

> Hello,
> 
> I would like to evaluate list comprehension expressions, from within
> which I'd like to call a function. For a first level it works fine but
> for second level it seems to lose the "_[1]" variable it uses internally
> to accumulate the results. Some sample code is:
> 
> class GetItemEvaluator(object):
>     def __init__(self):
>         self.globals = globals() # some dict (never changes)

Would you like to put a small wager on that?

>>> len(gie.globals)
64
>>> something_new = 0
>>> len(gie.globals)
65



>         self.globals["ts"] = self.ts
>         self.globals["join"] = "".join
>         self.locals = {} # changes on each evaluation
>     def __getitem__(self, expr):
>         return eval(expr, self.globals, self.locals)

Can you say "Great Big Security Hole"?

>>> gie = GetItemEvaluator()
>>> gie['__import__("os").system("ls")']
dicttest          dumb.py        rank.py        sorting
startup.py
0


http://cwe.mitre.org/data/definitions/95.html



-- 
Steven