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References: <87bnjhyohp.fsf@uriel.graune.org>
Date: Wed, 25 Mar 2015 13:41:02 -0400
Subject: Re: Supply condition in function call
From: Joel Goldstick <joel.goldstick@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Wed, Mar 25, 2015 at 1:29 PM, Manuel Graune <manuel.graune@koeln.de> wrote:
> Hi,
>
> I'm looking for a way to supply a condition to an if-statement inside a
> function body when calling the function. I can sort of get what I want
> with using eval (see code below) but I would like to achieve this in a
> safer way. If there is a solution which is safer while being
> less flexible, that would be fine. Also, supplying the condition as a
> string is not necessary. What I want to do is basically like this:
>
> def test1(a, b, condition="True"):
>     for i,j in zip(a,b):
>         c=i+j
>         if eval(condition):
>            print("Foo")
>
I'm not sure I understand your question, but condition will evaluate
to True or False regardless, so:
         if condition:
            print ("Foo")
         else:
            print ("Bar")

eval can be dangerous as someone could put some unknown command with
side effects in condition

> test1([0,1,2,3],[1,2,3,4],"i+j >4")
> print("Bar")
> test1([0,1,2,3],[1,2,3,4],"c >4")
> print("Bar")
> test1([0,1,2,3],[1,2,3,4],"a[i] >2")
> print("Bar")
> test1([0,1,2,3],[1,2,3,4])
>
> Resulting in
>
> Foo
> Foo
> Bar
> Foo
> Foo
> Bar
> Foo
> Bar
> Foo
> Foo
> Foo
> Foo
>
> Thanks for your help
>
> Regards,
>
> Manuel
>
> --
> A hundred men did the rational thing. The sum of those rational choices was
> called panic. Neal Stephenson -- System of the world
> http://www.graune.org/GnuPG_pubkey.asc
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-- 
Joel Goldstick
http://joelgoldstick.com