Lawful != Mutable (was Can Python function return multiple data?)

[felix]

El 07/06/15 12:20, Rustom Mody escribió:
> On Saturday, June 6, 2015 at 10:20:49 AM UTC+5:30, Steven D'Aprano wrote:
>> 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.
> Dunno why the fuss...
> As someone who often asks for short-simple-self-contained examples,
> I would have expected you to prefer clarity of communication over
> fidelity of experience??
>
> Anyways...
>
> Did I(rusi) now(2015) find that specific example surprising??
>
> No, but:
>
> 1. Questioners here regularly do show similar confusions.
> 2. I did go through similar decades ago when I first encountered programming
> 3. And most to the point, just add a little complexity and I (rusi-now)
> am as confused as any noob.
>
> A few weeks ago there was this example.
> It completely knocked me.
> ChrisA's exxplanation clarified.
> Here is a reconstruction based on Chris clarification
> [Chris do you remember the question?]
>
>>>> t=([1,2],[3,4])
>>>> t
> ([1, 2], [3, 4])
>>>> t[1] = t[1].append(5)
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> TypeError: 'tuple' object does not support item assignment
>>>> t
> ([1, 2], [3, 4, 5])
>
>> 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>
> Ok now rewrite that para above with
> s/tuple/numbers like 3 or 666/
> So I put '3' on the ram and grind it to finest powder.
> Have all trinities (of religious or secular variety) disappeared?
> 666 gone has the devil been banished from God's (or Steven's) universe?
>
>> 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.
> Actually its a very nice and apt quote.
> Just add laws of mathematics to laws of God and it will be perfect.
> [Or better remember that for Plato they were the same]
Interesting topic.
I'm a newbie to Python and programming.
I remembered that in the official Python tutorial I read this:

"...
TypeError: 'tuple' object does not support item assignment
 >>> # but they can contain mutable objects:
..."

Cheers.
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