>From my experience teaching Python to non-programmers, it's a huge
hurdle/nightmare to teach functions/methods that modify objects in-place
vs. return a value that must be reassigned. Behold Pandas's DataFrame's
sort method, which has an optional `in_place` argument that defaults to
*False*, which despite being a method that looks like mylist.sort(), works
differently from the method on lists, but more like the sorted *function*,
arrrgh! That was a fun session...
I think for consistency, having object methods that can act in-place
(semantics like mylist.pop, mylist.append are nice as Stéfane suggests)
only act in-place, and functions return a new object for reassignment would
help new users.
Maybe I'm teaching it poorly, suggestions welcome.
Nick
On Wed, Mar 1, 2017 at 11:26 AM, Stéfane Fermigier <s...@fermigier.com> wrote:
> Definitively not, just like M. Fowler: "Meyer likes to use command-query
> separation absolutely, but there are exceptions. Popping a stack is a good
> example of a query that modifies state. Meyer correctly says that you can
> avoid having this method, but it is a useful idiom. So I prefer to follow
> this principle when I can, but I'm prepared to break it to get my pop."
>
> What I wanted to point out is that the paragraph quoted by Stephan ("In
> general in Python (and in all cases in the standard library) a method that
> mutates an object will return None to help avoid getting the two types of
> operations confused. So if you mistakenly write y.sort() thinking it will
> give you a sorted copy of y, you’ll instead end up with None, which will
> likely cause your program to generate an easily diagnosed error.") doesn't
> seem to be true in this case.
>
> S.
>
> On Wed, Mar 1, 2017 at 6:23 PM, Cory Benfield <c...@lukasa.co.uk> wrote:
>
>>
>> On 1 Mar 2017, at 10:26, Stéfane Fermigier <s...@fermigier.com> wrote:
>>
>> Cf. https://martinfowler.com/bliki/CommandQuerySeparation.html
>>
>> But:
>>
>> >>> l = [1,2,3]
>> >>> l.pop()
>> 3
>> >>> l
>> [1, 2]
>>
>> => Not so true.
>>
>> S.
>>
>>
>> This is naturally a different circumstance: pop must return the element
>> it popped, otherwise it would just be del. Surely you aren’t suggesting
>> that pop should return self?
>>
>> Cory
>>
>
>
>
> --
> Stefane Fermigier - http://fermigier.com/ - http://twitter.com/sfermigier
> - http://linkedin.com/in/sfermigier
> Founder & CEO, Abilian - Enterprise Social Software -
> http://www.abilian.com/
> Chairman, Free&OSS Group / Systematic Cluster -
> http://www.gt-logiciel-libre.org/
> Co-Chairman, National Council for Free & Open Source Software (CNLL) -
> http://cnll.fr/
> Founder & Organiser, PyData Paris - http://pydata.fr/
> ---
> “You never change things by fighting the existing reality. To change
> something, build a new model that makes the existing model obsolete.” —
> R. Buckminster Fuller
>
>
>
> _______________________________________________
> Python-ideas mailing list
> Python-ideas@python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/
>
_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/
