[jhbadger]

Also, when he wrote it was kind of true. A lot of things hadn't been ported to Python 3 yet and using it was asking for pain. Now finally we are in the opposite situation where many things are ending support for Python 2 and the easier route is Python 3.

[thehardsphere]

He wrote his rant a few months ago, which was well after every major library switched to Python 3.

Dunno if you mean his previous book or the rant where he said, among other things, that Python 3 wasn't turing complete.

[jhbadger]

He updated it a few months ago, but he's had versions of this for quite some time. Yes, maintaining it in late 2016 is somewhat stubborn, but it made a lot of sense in the early years of Python 3.

[thehardsphere]

I have a difficult time believing that we're talking about the same rant, because the one I'm talking about would not have made any sense even in the early years of Python 3.

Oh, I see it's been updated with a sober disclaimer now, where "In the previous version I trolled people" and "I even had a note after the gag saying it was a gag, but everyone is too stupid to read that note even when they do elaborate responses to my writing."

I read his writing very carefully. This note didn't exist.

[thehardsphere]

For those of you now breaking out the Internet Archive to prove the note existed

> "Yes, that is kind of funny way of saying that there's no reason why Python 2 and Python 3 can't coexist other than the Python project's incompetence and arrogance. Obviously it's theoretically possible to run Python 2 in Python 3, but until they do it then they have decided to say that Python 3 cannot run one other Turing complete language so logically Python 3 is not Turing complete."

Even though he says it's a "funny" way to say something, his explanation of said "joke" is not a correct description of what Turing completeness is. There is no "gag" here; Zed didn't understand it, and when people on the internet corrected him, he decided to play it off as a gag.

Edit: Just to make it explicit for those of you reading who don't get it, "Turing completeness" doesn't mean "I can run a program written in X in Y's runtime." It means that a language is capable of expressing all operations a Turing machine can do, which means that you can re-write a program in X to a program in Y if both X and Y are Turing complete. You can obviously re-write a Python 2 program to be a Python 3 program, so both of those languages are Turing complete.

The property he describes later, of the JVM and the CLR supporting multiple languages has absolutely nothing to do with Turing completeness. Lisp and Javascript are both Turing complete languages, but the fact that you can't run Lisp on Node.js doesn't mean you can't re-write a Lisp program in Javascript. The fact that he's equating being able to run many languages on a single runtime and Turing compleness means he doesn't understand what he's talking about.

[webmaven]

>> Obviously it's theoretically possible to run Python 2 in Python 3, but until they do it then they have decided to say that Python 3 cannot run one other Turing complete language so logically Python 3 is not Turing complete."

> "Turing completeness" doesn't mean "I can run a program written in X in Y's runtime."

That's not quite what he meant. He meant that Turing completeness of both languages implies that an interpreter for Python 2 can be written in Python 3,and that if the Python maintainers say it isn't possible, etc. etc.

Which is technically true, except that it is completely obvious that the performance of Python 2 under that arrangement would so totally suck that no sane developer would ever take that approach (and I can believe that the Python maintainers just said "that won't work" or some such), and that is what he apparently didn't understand (or is now claiming he pretended not to understand for comedic effect).

[lmkg]

> "Turing completeness" doesn't mean "I can run a program written in X in Y's runtime."

It's not the definition of Turing Complete, but it is a provable property of Turing-Completeness. If Y is Turing-Complete, then you can use Y to write an interpreter for X. Then the issue is reduced to arguing about what the word "in" means in the phrase "run Python 2 in Python 3."

[thehardsphere]

Actually it's reduced to the words "in Python 3" because the conflation between the Python 3.x language and the CPython 3.x runtime is something that is prevalent throughout the document.

Just because the maintainers of CPython 3 haven't included a Python 2 interpreter doesn't mean that Python 3 is not Turing complete. Their choice not to do that has nothing to do with the Turing completeness of anything.

[derekp7]

> but the fact that you can't run Lisp on Node.js

But you can write a Lisp interpreter in Node.js, because they are both Turing complete. In fact, I believe I've seen tutorials written up on how to write a Lisp in Javascript.

[thehardsphere]

Let me clarify further.

The fact that Node.js, the software package that some people use to execute Javascript, does not include in it is default distribution a way to execute Lisp programs, says absolutely nothing about the Turing completeness of the Javascript programming language.

What those of you repeating this interpeter thing are missing is that there's a four term fallacy being employed here. Zed is trying to make an argument of the form:

If A, then B If B, then C Not C, therefore Not B

But in reality his argument is:

If A then B If B, then C Not D, therefore not B

[eastWestMath]

In other words:

http://i.imgur.com/pLOrJ.jpg

[sfilipov]

Agreed, it's not a problem of theoretical possibility. It's just that the maintainers' time can be better spent improving Python 3 than maintaining a Python 2 compatible runtime.

[srssays]

> You can obviously re-write a Python 2 program to be a Python 3 program, so both of those languages are Turing complete.

This is true, but the converse isn't true. e.g. Python and brainfuck are both turing complete, but Python has interfaces around a hell of a lot more syscalls than Brainfuck which only has operations for reading and writing from stdio. You can't write a Python implementation in brainfuck, it is impossible.

[thehardsphere]

No, that's just more work, because you have to write the required syscall interfaces for Brainfuck. There's nothing about Brainfuck that makes that impossible.

There's a difference between "impossible" and "really difficult giant waste of time" here when it comes to discussing Turing completeness.

[albedoa]

> I read his writing very carefully. This note didn't exist.

If only there were a machine with which we could go way back:

https://web.archive.org/web/20161123042252/https://learnpyth...

Yes, that is kind of funny way of saying that there's no reason why Python 2 and Python 3 can't coexist other than the Python project's incompetence and arrogance. Obviously it's theoretically possible to run Python 2 in Python 3, but until they do it then they have decided to say that Python 3 cannot run one other Turing complete language so logically Python 3 is not Turing complete. I should also mention that as stupid as that sounds, actual Python project developers have told me this, so it's their position that their own language is not Turing complete.

[joshuamorton]

If you check hacker news and reddit threads from the original posting, that note wasn't on the article when it was originally posted. It was only added later, but apparently still before anyone archived it.

Edit: I'm mistaken, however I'll say what I said then again:

The note does nothing to show that he actually understands the statements he's making. The note gets the definition of turing completeness wrong too.

[thehardsphere]

If you have a link proving that, I would love to see it. I completely believe you that it was added later, as it's my own recollection that there was no note.

But regardless, it doesn't change the fact that Zed wrote as if didn't know what he was talking about.

[phaemon]

You didn't read it carefully enough. It did exist.

It read:

"Yes, that is kind of funny way of saying that there's no reason why Python 2 and Python 3 can't coexist other than the Python project's incompetence and arrogance. Obviously it's theoretically possible to run Python 2 in Python 3, but until they do it then they have decided to say that Python 3 cannot run one other Turing complete language so logically Python 3 is not Turing complete. I should also mention that as stupid as that sounds, actual Python project developers have told me this, so it's their position that their own language is not Turing complete."

See: http://web.archive.org/web/20161123042252/https://learnpytho...

[emondi]

That was sarcasm against the impossibility of running python 2 code in the python 3 interpreter.

[thehardsphere]

I'm sure that defense is just as valid as "we were hacked and someone wrote all of those dumb things we said in exactly our writing style."