python 3's adoption

Daniel Fetchinson fetchinson at googlemail.com
Wed Jan 27 17:58:10 CET 2010


>>>>>>>     * Print is now a function. Great, much improvement.
>>>>> Actually not, IMHO. All it does is is to provide incompatibility.
>>>>
>>>> What incompatibility are you exactly talking about?
>>>>
>>>> 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
>>>>
>>>> Yes, this is with python 2.6.2 which is in the 2.x line of releases. So?
>>> I gather that your example is about code that technically executes fine
>>> with
>>> both versions and produces the same result, i.e. that there is a subset
>>> with
>>> the
>>> same syntax and semantics.
>>>
>>> But 'print' calls that technically execute fine with both versions may
>>> and
>>> will
>>> in general produce different results.
>>>
>>> I.e. not just the syntax but also the semantics have changed:
>>>
>>>
>>>  >>> import sys
>>>  >>> sys.version
>>> '2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)]'
>>>  >>>
>>>  >>> print( "2+2 =", 2+2 )
>>> ('2+2 =', 4)
>>>  >>> _
>>>
>>>
>>>  >>> import sys
>>>  >>> sys.version
>>> '3.1.1 (r311:74483, Aug 17 2009, 17:02:12) [MSC v.1500 32 bit (Intel)]'
>>>  >>>
>>>  >>> print( "2+2 =", 2+2 )
>>> 2+2 = 4
>>>  >>> _
>>
>> True. However, as someone else pointed out in a neighbouring thread you
>> can do
>>
>> 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.
>>>>> from __future__ import print_function
>>>>> print( "2+2 =", 2+2 )
>> 2+2 = 4
>>
>> which gives 100% compatibility as far as print is concerned between 2.6
>> and 3.x.
>
> That makes the code behave with 3.x syntax and semantics regarding print.
> I.e. it chooses one language.
>
> It doesn't make them compatible:

Of course it makes them compatible. I'm not saying any print-related
code in python 2.6 is valid python 3 code, but that it is *possible*
to write print-related code in python 2.6 that is also valid in python
3.

> if they were, then you wouldn't have to choose.

It seems to me you are arguing with the statement "Any print-related
python 2.6 code is valid python 3 code". Nobody is making this
statement. Let me repeat, what you should be arguing with is "It is
possible to write print-related python 2.6 code that is also valid
python 3 code". Perhaps I didn't make myself clear before, but at
least now I hope it's clear what I mean.

Cheers,
Daniel

> For example, it doesn't fix up 2.x code that prints tuples: incompatible, it
> will still execute but no longer do what it was supposed to do.
>
> But lest you focus down on that rare case, consider 2.x code that contains
>
>    print "2+2", 2
>
> All such statements need to be fixed up in a 2->3 transition. Adding
> __future__
> just makes the code invalid, it doesn't give you any shred of compatibility
> for
> this. A code rewrite can be partially automated like 2to3 but the
> incompatibility needlessly introduces an additional set of things that Can
> Go
> Wrong(TM), and with Murphy present, as He always is, well.
>
>
>> So again, what sort of an incompatibility are you talking about
>> concerning 'print' between 2.6 and 3.x?
>
> Syntax and semantics. They're different.


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