Question about ast.literal_eval

[Carlos Nepomuceno]

----------------------------------------
> To: python-list at python.org
> From: frank at chagford.com
> Subject: Re: Question about ast.literal_eval
> Date: Mon, 20 May 2013 09:50:02 +0200
>
> [Corrected top-posting]
>
>>> To: python-list at python.org
>>> From: frank at chagford.com
>>> Subject: Question about ast.literal_eval
>>> Date: Mon, 20 May 2013 09:05:48 +0200
>>>
>>> Hi all
>>>
>>> I am trying to emulate a SQL check constraint in Python. Quoting from
>>> the PostgreSQL docs, "A check constraint is the most generic constraint
>>> type. It allows you to specify that the value in a certain column must
>>> satisfy a Boolean (truth-value) expression."
>>>
>>> The problem is that I want to store the constraint as a string, and I
>>> was hoping to use ast.literal_eval to evaluate it, but it does not work.
>>>
>
> On 20/05/2013 09:34, Carlos Nepomuceno wrote:
>
>> It seems to me you can't use ast.literal_eval()[1] to evaluate that kind of expression
>> because it's just for literals[2].
>>
>> Why don't you use eval()?
>>
>
> Because users can create their own columns, with their own constraints.
> Therefore the string is user-modifiable, so it cannot be trusted.

I understand your motivation but I don't know what protection ast.literal_eval() is offering that eval() doesn't.

> Frank
>
>
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