Lisp mentality vs. Python mentality

[Ciprian Dorin, Craciun]

On Sun, Apr 26, 2009 at 7:54 AM, Steven D'Aprano
<steve at remove-this-cybersource.com.au> wrote:
> On Sat, 25 Apr 2009 10:50:50 +0300, Ciprian Dorin, Craciun wrote:
>
>> On Sat, Apr 25, 2009 at 10:43 AM,  <bearophileHUGS at lycos.com> wrote:
>>> Ciprian Dorin, Craciun:
>>>> Python way:
>>>> ---------
>>>> def eq (a, b) :
>>>>     return a == b
>>>>
>>>> def compare (a, b, comp = eq) :
>>>>     if len (a) != len (b) :
>>>>         return False
>>>>     for i in xrange (len (a)) :
>>>>         if not comp (a[i], b[i]) :
>>>>             return False
>>>>     return True
>>>
>>> That's not "pythonic".
>>>
>>> Bye,
>>> bearophile
>>> --
>>> http://mail.python.org/mailman/listinfo/python-list
>>
>>     Ok... Then what's pythonic? Please give a pythonic implementation...
>
> Don't re-invent the wheel. Instead of creating your own functions, use
> existing tools to your advantage.
>
> import operator
>
> def compare(a, b, comp=operator.eq):
>     if len(a) != len(b):
>         return False
>     for a, b in zip(a, b):
>         if not comp(a[i], b[i]):
>             return False
>     return True
>
>
> But we can re-write that to be even more pythonic, by using the built-in
> all():
>
> def compare(a, b, comp=operator.eq):
>     if len(a) != len(b):
>         return False
>    return all(comp(x, y) for (x, y) in zip(a, b))
>
> or even:
>
> def compare(a, b, comp=operator.eq):
>     return (len(a) == len(b)) and all(comp(*t) for t in zip(a, b))
>
>
> (All the above are untested, so please excuse any errors.)
>
>
>>     Ciprian Craciun.
>>
>>     P.S.: Also, I'm tired of hearing about the pythonic way... Where
>> do I find a definitive description about the pythonic way?
>
> There is no such thing as a definitive description of pythonic -- it is
> like art, and pornography: you can recognise it when you see it (except
> when you can't).
>
> However, you can get close by doing:
>
> import this
>
> in the Python interactive interpreter. Or from a shell prompt:
>
> python -m this
>
>
>> I think that
>> this word is used only when someone sees something that he doesn't like,
>> he doesn't know what he doesn't like at it, and just goes to say its
>> un-pythonic, without saying what would be... Wouldn't be just easier to
>> say "I don't know" or "I doesn't feel right to me"?
>
> I think that there's a risk that people over-use unpythonic when they
> mean "I don't like it", but that doesn't mean that pythonic isn't a
> meaningful concept. However, it is a matter of degree, not kind: like
> mole-hills and mountains, unpythonic and pythonic are very different
> things, but there's no precise dividing line between them.
>
>
> --
> Steven

    I liked very much your implementation for the compare function, it
is very short and at the same time readable:

> def compare(a, b, comp=operator.eq):
>     return (len(a) == len(b)) and all(comp(*t) for t in zip(a, b))

    But I have only one problem, it is suboptimal, in the sense that:
    * it constructs two intermediary lists (the list comprehension and
the zip call);
    * it evaluates all the elements, even if one is false at the beginning;

    So, could you overcome these problems?

    About the pythonic vs unpythonic words, I agree with you, there
are ofter overused and misused...

    Ciprian.