Python "why" questions

Ryan Kelly ryan at rfk.id.au
Sat Aug 7 05:36:03 CEST 2010


On Fri, 2010-08-06 at 22:05 -0500, Default User wrote:
> >From "the emperor's new clothes" department:
> 
> 1)  Why do Python lists start with element [0], instead of element
> [1]?  "Common sense" would seem to suggest that lists should start
> with [1].  

"Common sense" is wrong.  There are many compelling advantages to
numbering from zero instead of one:

  http://lambda-the-ultimate.org/node/1950

> 2)  In Python 3, why is print a function only, so that: print "Hello,
> World" is not okay, but it must be print("Hello, World") instead?
> (Yeah, I know: picky, picky . . . )

The real question is, why was print so special in Python 2 that is can
be called without parentheses?  The answer was "no reason" and it was
fixed in Python 3 to be consistent with the rest of the language.

> 3)  In Python 3, why does 2.0 / 3.0 display as 0.6666666666666666, but
> 8 * 3.57 displays as 28.56 (rounded off to 2 decimal places)?  And
> yet, in Python 2.6, 8 * 3.57 displays as 28.559999999999999?

Because the code for displaying floats was improved in python 3.  You
can follow the fascinating discussion on issue 7117:

   http://bugs.python.org/issue7117

I can't defend the rounding issues of floating point numbers in general
- it's just "one of those things" that you have to deal with.  But show
me a language where floats don't have this problem.

> And we wonder why kids don't want to learn to program.  

Yeah, obscure language warts, that must be the reason.

Note to self:  DNFTT...


  Ryan

-- 
Ryan Kelly
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