Python "why" questions
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From: Thomas Jollans on 7 Aug 2010 08:00 On 08/07/2010 05:05 AM, 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]. As others have pointed out, there is a nice argument to be made for zero-based indices. However, the killer reason is: "it's what everybody else does." As it stands, the only perceived problem with zero-based indices is that it's one of the many tiny confusions that new programmers face. On the other hand, it's the way nearly every other popular programming language does it, and therefore, it's the way almost every programmer likes to think about sequences. Also, it has the nice property that, for an infinite sequence, every integer makes sense as an index (in Python). > > 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 . . . ) > > 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? 0:pts/3:~% python3.1 Python 3.1.2 (release31-maint, Jul 8 2010, 09:18:08) [GCC 4.4.4] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 28.56 28.56 >>> 0:pts/3:~% python2.6 Python 2.6.6rc1+ (r266rc1:83691, Aug 5 2010, 17:07:04) [GCC 4.4.5 20100728 (prerelease)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 28.56 28.559999999999999 >>> 0:pts/3:~% same number - why use more digits if you can avoid it? Python 3 is smart enough to avoid it. > > And we wonder why kids don't want to learn to program. Don't kids want to learn to program? Many don't, a fair bunch do. It's the same for any other art. Also, the only people that realize this kind of "issue" are those that have already learned programming.
From: D'Arcy J.M. Cain on 7 Aug 2010 08:54 On Sat, 07 Aug 2010 13:48:32 +0200 News123 <news1234(a)free.fr> wrote: > It makes sense in assembly language and even in many byte code languages. > It makes sense if you look at the internal representation of unsigned > numbers (which might become an index) > > For a complete beginner common sense dictates differently and there > might be confusion why the second element in a list has index 1. Would said beginner also be surprised that a newborn baby is zero years old or would it be more natural to call them a one year old? Zero based counting is perfectly natural. -- D'Arcy J.M. Cain <darcy(a)druid.net> | Democracy is three wolves http://www.druid.net/darcy/ | and a sheep voting on +1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.
From: Roald de Vries on 7 Aug 2010 09:37 On Aug 7, 2010, at 2:54 PM, D'Arcy J.M. Cain wrote: > On Sat, 07 Aug 2010 13:48:32 +0200 > News123 <news1234(a)free.fr> wrote: >> It makes sense in assembly language and even in many byte code >> languages. >> It makes sense if you look at the internal representation of unsigned >> numbers (which might become an index) >> >> For a complete beginner common sense dictates differently and there >> might be confusion why the second element in a list has index 1. > > Would said beginner also be surprised that a newborn baby is zero > years > old or would it be more natural to call them a one year old? Zero > based counting is perfectly natural. A new born baby is in his/her first year. It's year 1 of his/her life. For this reason, also "the year 0" doesn't exist. From the fact that a baby can be half a year old, you derive that arrays should have floats as indices?
From: Steven D'Aprano on 7 Aug 2010 09:38 On Sat, 07 Aug 2010 14:00:59 +0200, Thomas Jollans wrote: > On 08/07/2010 05:05 AM, 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]. > > As others have pointed out, there is a nice argument to be made for > zero-based indices. However, the killer reason is: "it's what everybody > else does." I'll have you know that there are still some Pascal programmers in the world, thank you. > As it stands, the only perceived problem with zero-based > indices is that it's one of the many tiny confusions that new > programmers face. On the other hand, it's the way nearly every other > popular programming language does it, and therefore, it's the way almost > every programmer likes to think about sequences. It didn't take me long to get used to thinking in zero-based indexes, but years later, I still find it hard to *talk* in zero-based indexes. It's bad enough saying that the first element in a list in the zeroth element, but that the second element is the first makes my head explode... > Also, it has the nice property that, for an infinite sequence, every > integer makes sense as an index (in Python). Er, what's the -1th element of an infinite sequence? -- Steven
From: D'Arcy J.M. Cain on 7 Aug 2010 09:53
On Sat, 7 Aug 2010 15:37:23 +0200 Roald de Vries <downaold(a)gmail.com> wrote: > > Would said beginner also be surprised that a newborn baby is zero > > years > > old or would it be more natural to call them a one year old? Zero > > based counting is perfectly natural. > > A new born baby is in his/her first year. It's year 1 of his/her life. > For this reason, also "the year 0" doesn't exist. From the fact that a > baby can be half a year old, you derive that arrays should have floats > as indices? No. You are giving me math and logic but the subject was common sense. Common usage counts ages as years with the second year called "one year old" so zero based counting is common. We don't tell Aunt Martha that little Jimmy is in his third year. We say that he is two years old and Aunt Martha, a non-programmer, understands exactly what we mean. Using one-based counting (first year, second year, etc.) would be the unnatural thing, would confuse Aunt Martha and make her spoil her apple pie and no one wants that. -- D'Arcy J.M. Cain <darcy(a)druid.net> | Democracy is three wolves http://www.druid.net/darcy/ | and a sheep voting on +1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner. |