Multi-dimensional list initialization

Andrew Robinson andrew3 at r3dsolutions.com
Wed Nov 7 23:22:35 CET 2012


On 11/06/2012 10:56 PM, Demian Brecht wrote:
> My question was *not* based on what I perceive to be intuitive 
> (although most of this thread has now seemed to devolve into that and 
> become more of a philosophical debate), but was based on what I 
> thought may have been inconsistent behaviour (which was quickly 
> cleared up with None being immutable and causing it to *seem* that the 
> behaviour was inconsistent to the forgetful mind).
I originally brought up "intuitive"; and I don't consider the word to 
mean an "exclusive" BEST way -- I meant it to mean easily guessed or 
understood.  An intelligent person can see when there may be more than 
one reasonable explanation -- ergo: I just called your OP intelligent, 
even if you were wrong; and D'Aprano ripped you for being wrong.

The debate is degenerating because people are _subjectively_ judging 
other people's intelligence.
The less intelligent a person is, the more black and white their 
judgements _tend_ to be.

> As you touch on here, "intuition" is entirely subjective. If you're 
> coming from a C/C++ background, I'd think that your intuition would be 
> that everything's passed by value unless explicitly stated.
Yup -- that's my achillies heel and bias, I'm afraid.
I learned basic, then assembly, and then pascal, and then fortran77 with 
C (historically in that order)

In my view, pass by value vs. reference always exists at the 
hardware/CPU level regarless of the language; and regardless of whether 
the language hides the implementation details or not;

I'm an EE; I took software engineering to understand the clients who use 
my hardware, and to make my hardware drivers understandable to them by 
good programming practices.  An EE's perspective often lead to doing 
efficient things which are hard to understand;  That's why I look for a 
consensus (not a compromise) before implementing speed/memory 
improvements and ways to clarify what is being done.

> Someone coming from another background (Lua perhaps?) would likely 
> have entirely different intuition. 
Yes, they might be ignorant of what LUA is doing at the hardware level; 
even though it *is* doing it.

>> So while I prefer intuitively obvious behaviour where possible, it is not
>> the holy grail, and I am quite happy to give it up.
> I fail to see where there has been any giving up on intuitiveness in the context of this particular topic. In my mind, intuitiveness is generally born of repetitiveness and consistency.
YES!!!!  I think a good synonym would be habit;  and when a habit is 
good -- it's called strength, or "virtue"; When it's bad it's called 
"vice" or "sin" or "bad programming habit."  :)
Virtues don't waste people's time in debugging.
>   As everything in Python is a reference, it would seem to me to be inconsistent to treat expressions such as [[obj]*4]*4 un-semantically (Pythonically speaking) and making it *less* intuitive. I agree that Python would definitely be worse off.
That's a fair opinion. I was pleasantly surprised when the third poster 
actually answered the "WHY" question with the idea that Python always 
copies by reference unless forced to do deep copy.  That's intuitive, 
and as a habit (not a requirement) Python implements things that way.

I've already raised the question about why one would want a multiplier 
at all, if it were found that the main desired use case never *wants* 
all objects to change together.

I laid out a potential modification of list comprensions; which, BTW, 
copy by re-instantiating rather than reference; so the paradigm of 
Python is wrong in that case....  But, I think the modifications in that 
context can't be argued against as easily as list multiplication (For 
the same reason that comprehensions already break the copy by reference 
mold !!!! )



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