Can Python function return multiple data?

[Steven D'Aprano]

On Sat, 6 Jun 2015 01:20 pm, Rustom Mody wrote:

> On Saturday, June 6, 2015 at 3:30:23 AM UTC+5:30, Chris Angelico wrote:

>> Congrats! You just proved that an object can itself be immutable, but
>> can contain references to mutables. Ain't that awesome?
>> 
>> Did you have a point?
> 
> [Under assumption you are not being facetious...]
> The word immutuable happens to have existed in English before python.
> I also happen to have used it before I knew of python
> The two meanings do not match
> I am surprised
> Is that surprising?

Yes, I am surprised that you are surprised. You have been a regular, and
prolific, contributor on this forum for some years now, teach Python, blog
about it. You're quite obviously well-read and experienced. How is it that
you are surprised by such a fundamental part of not just Python's object
model, but of real life objects too?

I suspect you are pretending to be surprised to make a rhetorical point.

Like many English words, "immutable" has a few meanings in plain English.
Bouvier's Law Dictionary included in 1856 this definition:

    IMMUTABLE. What cannot be removed, what is unchangeable.
    The laws of God peing perfect, are immutable, but no 
    human law can be so considered.

Clearly tuples can be removed. They are garbage-collected like any other
values in Python. If nothing else, you can turn the computer off, remove
the RAM, grind it down into the finest powder, and scatter it to the winds.
That surely is enough to remove the tuples <wink> 

So according to Bouvier's definition, tuples are not immutable. But I trust
that we can agree that Bouvier's definition is not useful here.

In object-oriented programming circles, including Python, the relevant
definition is that you cannot add or remove elements from the tuple once it
is instantiated. That is all. If those elements happen to be mutable
themselves, they don't cease to be mutable just because you happen to have
put them in a tuple. This does not happen:

    mylist = []
    mytuple = (None, 1, mylist)
    mylist.append(0)
    => raises an exception

The *tuple* is immutable, not the list. The elements of the list are not
elements of the tuple and don't participate in the guarantee of
tuple-immutability.


> As a parallel here is Dijkstra making fun of AI-ers use of the word
> 'intelligent'
>  http://www.cs.utexas.edu/users/EWD/transcriptions/EWD06xx/EWD618.html

Nice rant, but as is typical of so many rants by Dijkstra, it's overflowing
with smugness at his own cleverness, and very light on actual reasoning or
sense.


-- 
Steven