How to convert a list of strings into a list of variables

Steven D'Aprano steve+comp.lang.python at pearwood.info
Fri Aug 19 03:42:24 CEST 2011


Chris Angelico wrote:

> On Thu, Aug 18, 2011 at 5:09 PM, John Gordon <gordon at panix.com> wrote:
>> for x in list_of_strings:
>> list_of_variables.append(eval(x))
>>
> 
> If this really is what you need, you can simplify it by using the
> globals() dictionary - it's a regular dictionary whose contents are
> all the global variables in your current module. Inside a function,
> use locals() instead.

You can use locals outside of a function too, because it just returns
globals().

Lookup of names in locals/globals is much safer than eval, particularly if
there is any risk that the list of names comes from an untrusted or 
potentially hostile source.

list_of_strings = ['red', 'blue', 
    '__import__("os").system("echo I just p0wned your system")',
    'green', 'yellow']

(The simplest way out of a billion to cause grief.)

Code injection attacks are the first and second most common form of security
vulnerability, ahead of even buffer overflows. Please don't add to the
list.

http://cwe.mitre.org/top25/?2011

(Oh, and if you think that protecting against code injection attacks while
still using eval or exec is simple, please step away from the keyboard.)



-- 
Steven




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