On Jan 27, 9:22 am, Daniel Fetchinson <fetchin...@googlemail.com> wrote: > >> Hi folks, > > >> I was going to write this post for a while because all sorts of myths > >> periodically come up on this list about python 3. I don't think the > >> posters mean to spread false information on purpose, they simply are > >> not aware of the facts. > > >> My list is surely incomplete, please feel free to post your favorite > >> misconception about python 3 that people periodically state, claim or > >> ask about. > > >> 1. Print statement/function creates incompatibility between 2.x and 3.x! > > >> Certainly false or misleading, if one uses 2.6 and 3.x the > >> incompatibility is not there. Print as a function works in 2.6: > > >> Python 2.6.2 (r262:71600, Aug 21 2009, 12:23:57) > >> [GCC 4.4.1 20090818 (Red Hat 4.4.1-6)] on linux2 > >> Type "help", "copyright", "credits" or "license" for more information. > >>>>> print( 'hello' ) > >> hello > >>>>> print 'hello' > >> hello > > >> 2. Integer division creates incompatibility between 2.x and 3.x! > > >> Again false or misleading, because one can get the 3.x behavior with 2.6: > > >> Python 2.6.2 (r262:71600, Aug 21 2009, 12:23:57) > >> [GCC 4.4.1 20090818 (Red Hat 4.4.1-6)] on linux2 > >> Type "help", "copyright", "credits" or "license" for more information. > >>>>> 6/5 > >> 1 > >>>>> from __future__ import division > >>>>> 6/5 > >> 1.2 > > >> Please feel free to post your favorite false or misleading claim about > >> python 3! > > > Well, I see two false or misleading claims just above - namely that > > the two claims above are false or misleading. They tell just half of > > the story, and that half is indeed easy. A Python 3 program can be > > unchanged (in the case of print) or with only trivial modifications > > (in the case of integer division) be made to run on Python 2.6. > > Okay, so we agree that as long as print and integer division is > concerned, a program can easily be written that runs on both 2.6 and > 3.x. > > My statements are exactly this, so I don't understand why you disagree. > > > The other way around this is _not_ the case. > > What do you mean? > > > To say that two things are > > compatible if one can be used for the other, but the other not for the > > first, is false or misleading. > > I'm not sure what you mean here. Maybe I didn't make myself clear > enough, but what I mean is this: as long as print and integer division > is concerned, it is trivial to write code that runs on both 2.6 and > 3.x. Hence if someone wants to highlight incompatibility (which surely > exists) between 2.6 and 3.x he/she has to look elsewhere.
I think you're misunderstanding what "compatibility" means in a programming language context. Python 3 and Python 2 are not mutually compatible, as arbitrary programs written in one will not run in the other. The most important fallout of that is that Python 3 is not backwards compatible, in that existing Python 2 programs won't run unaltered in Python 3--while it's easy to write a new program in a subset of the languages that runs on both Python 2 and 3, the huge existing codebase of Python 2 code won't run under Python 3. That there exists an intersection of the two languages that is compatible with both doesn't make the two languages compatible with each other--although it being a fairly large subset does help mitigate a sizable chunk of the problems caused by incompatibility (as do tools like 2to3). In your example, a python2 program that uses print and division will fail in python3. The print problem is less significant, since the failure will probably be a syntax error or a rapid exception raised. The division problem is more problematic, since a program may appear to run fine but silently misbehave; such errors are much more likely to result in significant damage to data or other long-term badness. -- http://mail.python.org/mailman/listinfo/python-list
