[Python-Dev] Improved evaluator added to ast module (original) (raw)

Daniel Holth dholth at gmail.com
Thu Oct 18 15:16:25 CEST 2012

On Thu, Oct 11, 2012 at 1:36 PM, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:

Daniel Holth <dholth gmail.com> writes:

How does this compare to the markerlib approach? In markerlib you just make sure all the AST nodes are in a set of allowed nodes, currently (Compare, BoolOp, Attribute, Name, Load, Str, cmpop, boolop), and then use the normal eval(). Is one way more secure / fast / flexible than the other? I don't think performance is an issue, and the markerlib approach seems just as reasonable as the one I've taken, except that it calls eval(), whereas my approach doesn't. It boils down to what should be allowed in expressions, and what shouldn't be. ISTM there is a space for a limited evaluator that's less limiting than literaleval(). I do realise that this type of sandboxing is not easy to achieve, and I'm not aiming to advance the state of the art here - I just want to close the issue in the best way I can.

I bet the literal_eval approach simply predates compile(ast) which is a Python 2.6 feature. It is also probably slightly faster on CPython to avoid compile(ast) if you are only evaluating the code once.

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