checking if a list is empty

[Algis Kabaila]

On Friday 13 May 2011 18:47:50 Hans Georg Schaathun wrote:
> On Thu, 12 May 2011 23:20:20 +1000, Chris Angelico
> 
>   <rosuav at gmail.com> wrote:
> :  Writing a program requires expertise both in programming
snip...
> 
> And the main difference here, is that the civil engineers
> have a much better language to share information.  The best
> programmers have is the programming language, and we ought
> to make that as good as possible.

As an old Civil Engineer and a retired educator of Civil and 
Aeronautical Engineers, I want to get at the end of the long 
thread.  Early in the thread I (wrongly) thought that the 
discussion just did not make sense.  Much as has been said, 
makes a good sense, though some of it is hardly relevant.  So 
what is the purpose of this discussion - is it to proffer advice 
to the "Benevolent Dictator for life" and to his cohort or is it 
to better understand the programming language Python?

In relation to the first part of the question is that the aim is 
far too ambitious - the success of Python language is enough to 
suggest that Guido and his team do not need advice and they will 
ask for it if they really do want to hear the opinions about it.  
The job they have done in developing the language is admirable 
and the users better concentrate on trying to understand it 
better.

The second part of the (rhetorical) question is that the answer 
depends what the designers of Python have chosen as criterion 
for "True" or "False". In my little effort to present Vector 
algebra in an easy to use manner
(refer to thread of yesterday: "Python 3.2 Vectors.py module")
it was necessary to answer the question of what could and what 
should be used to determine what the instruction '=='  or  '>='  
should mean and what should be used for comparison.  The only 
one that I could find useful was the equality - two vectors are 
equal if and only if all three of their components are equal.  
As the components (for purposes of engineering analysis) are 
real numbers, even the postulation of (v1.x == v2.x) is 
problematic, as has been pointed out in the thread (as the 
"floats" are subject to unavoidable round off errors).  So the 
answers are not necessarily unique and one must consider what 
the program is supposed to achieve.

BTW, the "Vector" class inherits from the list, which  avoids 
"reinventing the wheel". The other operators are assigned 
specific purposes, viz. v1 * v2 is a scalar product of two 
vectors (the result is a scalar, float), while v1 * r  (where v1 
is a vector and r is a float) is scaling the size of vector by 
factor r,  (the result is a vector) i.e. each component of v1 is 
multiplied by r.

Vector product (cross product) is shown as  v1 ** v2 (the result 
is a vector).  The purpose of choosing this scheme is neither 
linguistic, nor philosophical - it is practical, just as the 
vector algebra is practical.  It helps to visualise solutions of 
physical problems (or, if you prefer, engineering problems).

OldAl.
-- 
Algis
http://akabaila.pcug.org.au/StructuralAnalysis.pdf
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