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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Coolest Python recipe of all time
Date: Tue, 03 May 2011 02:00:05 -0400
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:4526

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).

-- 
Terry Jan Reedy