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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: How convert a list string to a real list
Date: Wed, 30 Nov 2011 17:12:10 -0500
References: <CAHbqn4jog2CzT+ahL3XwPZwvAr8eKN3qHsp2yaJk1VYa1157JQ@mail.gmail.com> <jb4jv2$4nt$1@dough.gmane.org> <jb4r6o$ifb$1@dough.gmane.org>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:16454

On 11/30/2011 3:58 AM, Peter Otten wrote:
> Terry Reedy wrote:
>
>> On 11/30/2011 1:20 AM, =E9=83=AD=E5=86=9B=E6=9D=83 wrote:
>>> Good after
>>> I have a string liststr =3D '["aaaa","bbbb","ccc"]' ,and I need conve=
rt it
>>> to a list like list =3D ["aaaa","bbbb","ccc"],what can id do?
>>
>> The easiest -- and most dangerous -- way is
>>   >>>  eval('["aaaa","bbbb","ccc"]')
>> ['aaaa', 'bbbb', 'ccc']
>>
>> But DO NOT eval unexamined strings from untrusted sources. The reason =
is
>> that it is much the same as letting an untrusted person sit unsupervis=
ed
>> as the keyboard of your computer with a command window open. You would=

>> not want to eval
>>     "from os import system; system('<command to delete files>')"
>> where '<command...>' is replaced by something obnoxious for your
>> operating system.
>
> You can avoid these problems with ast.literal_eval():
>
> literal_eval(node_or_string)
>      Safely evaluate an expression node or a string containing a Python=

>      expression.  The string or node provided may only consist of the
>      following Python literal structures: strings, numbers, tuples, lis=
ts,
>      dicts, booleans, and None.

I keep forgetting that someone thought to solve the problem of eval=20
being both convinient and dangerous. Maybe if I type it once, I will=20
remember.
 >>> import ast
 >>> ast.literal_eval('["aaaa","bbbb","ccc"]')
['aaaa', 'bbbb', 'ccc']

I think it would be better if safe_eval were available as an easily=20
accessible builtin and dangerous_eval were tucked away in a module ;-).

--=20
Terry Jan Reedy