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From: Stefan Behnel <stefan_ml@behnel.de>
Subject: Re: Coolest Python recipe of all time
Date: Tue, 03 May 2011 08:23:58 +0200
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:4528

Terry Reedy, 03.05.2011 08:00:
> On 5/3/2011 1:04 AM, Stefan Behnel wrote:
>
>> The bad thing about this recipe is that it requires quite a bit of
>> background knowledge in order to infer that the code the developer is
>> looking at is actually correct.
>
> The main math knowledge needed is the trivial fact that if a*x + b = 0,
> then x = -b/a. The other math knowledge needed is that complex numbers add
> componentwise. The trick is that replacing x with j and evaluating
> therefore causes (in Python) all the coefficients of x (now j) to be added
> together separately from all the constant terms to reduce the linear
> equation to a*x+b (= 0 implied).

As your above paragraph proves, it's the kind of implementation that 
requires three lines of executing code and at least 6 lines of additional 
comment. Hopefully accompanied by an excuse of the developer.

Stefan