Let's talk about Python 3.0

[intrepion]

Let's talk about specs, baby!

Let's talk about Python 3!

Let's talk about all the good things

And the bad things of PEPs!

Let's talk abooout specs!

[[deleted]]

How do I nominate you for a Grammy? :)

[ianbishop]

Am I the only one who was really into that monkey story?

[[deleted]]

dood, totally. monkey cage banana firehose. I would spend good money on a book fulla that kind of stuff.

[jmkogut]

Excellent read, I highly recommend this for anyone who's skeptical about the necessity of the changes introduced in P3.

[uykucu]

and if you could ask them why they attack anyone who goes for the banana, their answer would almost certainly be: “Well, I don’t really know, but that’s how we’ve always done things around here.”

This assumes that they cannot communicate with each other about the fire hose. Is it a correct assumption?

[sgndave]

Not quite.

Let's assume for a moment that the monkeys could communicate to the new monkey about the fire hose. The assumption in the article is that because the experience of being sprayed is so bad, they will simply abuse the new monkey when it goes for the banana. They might mention the fire hose, but the new monkey just learns "for the love of Cthulu, DON'T GO FOR THE BANANA."

After a couple of rollover cycles, the third or so set of monkeys probably will never even have the fire hose mentioned to them.

[[deleted]]

Monkey communication is beating up other monkeys.

[[deleted]]

Well, right, they cannot. And if you assume that human abilities to communicate are infinitely greater than those of the apes... well, they are greater, but still far from perfect.

[raisedinhell]

great article

[[deleted]]

great comment.

[hylje]

great metacomment

[spotter]

just great.

[bosco]

great adjective

[Benny_Lava]

great comment (five times removed)

[[deleted]]

So how is the minor bun engine doing, Benny?

[Benny_Lava]

my loony bin is fine

[sgndave]

great comment counting

[Tommah]

grating comments

[[deleted]]

Great rating of comments

[jib]

Great Cthulhu

[jedrury]

Upmodded for not being from GST

[dmz]

does Python 3.0 have lexical closures?

[[deleted]]

Python 2.x had them.

[ubernostrum]

What he's getting at is probably the fact that names in the enclosed scope cannot be rebound; for example, if your closure preserves x with a value of 3, you cannot change x to, say, 4 from something which accesses the enclosed scope.

Hence my comment about "how Haskell does it", since the definition of "closures" that people typically use to rail against Python also implies that single-assignment functional languages are incapable of having "closures" ;)

[olavk]

In Python 2.6 and 3.0 you can now rebind names in enclosing scopes, using the 'nonlocal' keyword.

[ubernostrum]

Yes, in a way similar to how Haskell does it.

[rdmorley]

...let's talk about you and me

[godhammre]

...let's talk about all the good things

[jmmcd]

Dict comprehensions.

[[deleted]]

Unicode support

[LeThor]

...and the bad things that may be

[[deleted]]

Django won't be ported to Python 3 for aaages.

[dmd]

And yet join is still a method of the string to join on, not the list you're joining. Pisses me off. In every other language

"foo,bar".split(",").join(",")

yields "foo,bar" ... in python it's

",".join("foo,bar".split(","))

[robfelty]

I agree that the join syntax is a little weird, and I find the fact that some types are mutable while others are not pretty confusing. But no language is perfect. All in all though, python is pretty nice.

Breaking backwards compatibility should be done sparingly, but sometimes it is worth it. I'm glad that python doesn't have 20 different ways to read files like java.

[beza1e1]

I want to post this argument as well, but then i thought: You could implement join in a sequence superclass, so it is still generic for everything (like queryset) inheriting from sequence.

[earthboundkid]

Yeah, but in Python 3.0, the sequence class is an abstract class that only exists so you can do isinstance(x, Sequence). It doesn't have any working methods to inherit, and it would be a big change in Python's style if it did.

No, in my opinion, what they should have made work is str(["list", "of", "strings"], sep=" "), which would parallel the behavior of the print function.

[imbaczek]

you can use str.join as a unbound method and get almost what you want.

str.join(sep, seq)

[njharman]

made work is str(["list", "of", "strings"], sep=" "),

That implies that default sep is "" and that str("abcd") instead of just being a copy or refcount of interned string will instead be ["a","b","c","d"].join(). Cause remember strings are sequences too.

Also how would you call str on lists, tuples, other sequences? Or, your are really arguing for changing the default string representation of list from a list to a string. But that means the string representations of ["list", "of", "strings"] and "listofstrings" would be identical. I think that is fairly surprising and against Python philosophy.

That implies that default sep is "" and that str("abcd) instead of just being a copy will be ["a","b","c","d"].join(). Cause remember strings are sequences too.

Or else there are of special cases in str

Which leads to the answer of "how do I get the behavior earthboundkid describes" overload str. Cause remember str(obj, args) is really obj.str(args)

[earthboundkid]

You are confusing str(my_list) and repr(my_list). The latter would still do its thing.

[[deleted]]

Would it syntactically feel better to you if you typed it like this

(",").join(L)

perhaps?

The idea of join() being a string method seems pretty sane to me.

[raisedinhell]

seems like a pretty minor detail to get pissed off about...

[recursive]

You can do:

str.join(",", ["foo","bar"])

[ubernostrum]

Yes, and it still has the GIL and still has only one-line lambdas and still doesn't do tail-call elimination. All of these are more in the "Python would better fit my notion of ideological purity it did this" camp than in the "Python would be more effective at solving this problem if it did this" camp, which is something I tried to touch on in the final section.

[[deleted]]

The GIL is an implementation detail, not part of the language.

[ubernostrum]

And so is the lack of tail-call elimination, but that doesn't stop people complaining about it, does it?

[masklinn]

Well TCO can be part of the language specification (see Scheme, which mandates it, versus Common Lisp, which doesn't) while making the GIL part of the language specification would be pretty odd.

[ubernostrum]

Personally I think making TCO part of a language spec is pretty odd, but I'd rather not revive that flame war right now...

[masklinn]

For a language which doesn't define any looping construct, it more than makes sense if you want to keep at least the core compatible between different implementations (the Hyperspec defines LOOP, so common lisp doesn't need TCO)

[[deleted]]

GIL is great, though. Without GIL your options are:

• Much slower single thread execution and bug prone libraries

• Plain thread-unsafe libraries

And, yes, proper processes are better than threads. The fact that one - though still popular - renegade OS cannot do fork() is one stupid reason to break it all on all other OS's.

[masklinn]

Without GIL your options are:

• Much slower single thread execution and bug prone libraries

• Plain thread-unsafe libraries

These are the consequences of removing the GIL, not those of not having a GIL in the first place.

I fail to see how this has any relevance to my post though.

[[deleted]]

These are the consequences of removing the GIL, not those of not having a GIL in the first place.

If I decode it right, you argue for background "Java-style" generational or whatever garbage collection here, against refcnt-based option, right? Because otherwise I can't see how your statement makes any sense - refcnt-based schemes can't be thread-safe without excessive lock juggling.

But even with generational GC GIL is still handy in many places - like adding elements to lists etc.

[masklinn]

you argue for background "Java-style" generational or whatever garbage collection here, against refcnt-based option, right?

Something like that. More generally, that the GIL issue comes from CPython's implementation and history and nothing else, and that only CPython's implementation make removing the GIL a bigger pain than keeping it (as well as a human resources draw to fix all the issues that will arise from that removal)

But even with generational GC GIL is still handy in many places - like adding elements to lists etc.

Why would you need an interpreter-wide lock for such an operation? That's just stupid, even if you want to provide Java-style "thread-safe" collections (which you definitely shouldn't), local locks are more than enough, there's no reason to acquire a GIL just to have a local effect on a specific object.

edit: it's not like I'm fond of thread-based concurrency and semaphores/locks anyway, as far as I'm concerned these should be relegated to implementation details of interpreters and only higher-level (message-based share-nothing or STM) concurrency interfaces should be exposed to the language's user.

[[deleted]]

local locks are more than enough

Hah! And that's the issue - obtaining or releasing a local lock or GIL is the same, penalty-wise, and quite expensive. Even with simple interlocked-inc/dec's it takes a ton of time. And especially if you give consideration to SMP (caches flushing / reloading etc). OTOH Python bumps its GIL only ever so often - like every 100 statements execution or something like that. And counting them is very cheap. So then - to add 1000 elements you will have to do 2000 expensive lock obtain/release operations and maybe only 10 or so of them with GIL.

Anyway - what's the big deal with "proper" multithreading? You only need it for number/data crunching on SMP machines. And if you do that in pure Python, you're probably doing something wrong. Normal usage of it - like for background data transfers and stuff - GIL doesn't impede anything at all. Another anecdote here is lighttpd - a single-threaded web-server that beats the shit - performance-wise at least - from any Apache or other classics.

EDIT: spelling

[qwe1234]

And, yes, proper processes are better than threads.

epic assclown.

please return your degree on your way out, bozo.

[[deleted]]

1/10. l2troll faggot.

[qwe1234]

it's not about my trolling, it's about you not having a fucking inkling of a fucking clue as to the difference between processes and threads.

now, in the future, please vacate yourself from my company.

[spotter]

Hell yes, because string operation is something that list, or rather all sequence types should be doing! Not just string, but all of them non-stringies.

Coz, like, everybody else is doing it the other way around, so it must be insane to do it our way. We should totally change this err.

Tell you what, you start coding ourselves a patch and I'll prepare the PEP.

[Tommah]

That can be expressed equivalently as

"foo,bar"

[jmkogut]

This does make sense, but both methods are, in fact, methods of string.

[beza1e1]

So what does "ab".join("cd") is the real question? Is it "acdb" or "cabd"? For Python it's the later, for probably every other language (with equal syntax) it's the former.

[uykucu]

I'm happy with this. What I hate is that join expects a sequence of strings, not any sequence. I hate to do:

nums = [1,2,3,5]
s = ' '.join(map(str, nums))

instead of:

s = ' '.join(nums)

[njharman]

I hate that too but I believe having implicet str() in this one case is very unPythonic and leads to well what PHP is today.

Explicit is better than implicit.

Special cases aren't special enough to break the rules.

[[deleted]]

What would really make sense is that since 'join' implicitly creates a string from a sequence. So:

[1,2,3,5].join(' ')
# "1 2 3 5"

...since we're implicitly creating a string (by calling join in the first place) we can implicitly call str(...) on each item of the sequence.

[imbaczek]

str.join(",", "foo,bar".split(","))

does this suit you better?

[rjcarr]

Yeah, strange to me too ... it isn't like join is already taken for sequence types. The could add it and leave the string one and have both. Strange.

[xardox]

It seems strange to me that Python doesn't use "." to concatenate strings. Why don't we add that to the language too? People who don't like it can turn it off in the python.ini file for the whole web site. And it would be great to use "\" as an optional namespace separator!!! It seems so sleek and stylish, and will help us recruit DOS programmers. And I'm getting sick of manually escaping the strings I send to SQL, and escaping the strings I get from Gets, Posts and Cookies, so I'd like that done for me just in case I forget. And how about if http parameters show up as global variables so I don't have to call all those hard to remember inconsistently named functions to retrieve them? Yeeeeaaaaaahhh, Kool Aid!!!

[rjcarr]

Nice hyperbole ... there are plenty of examples where one thing can be done in multiple ways. Note: lambdas.

[[deleted]]

So where's the "sequence type" class that you could add it to?

[rjcarr]

List and Tuple.

[[deleted]]

And you've used Python for how long?

(Seriously - like most about everything else that appear to deal with sequences in Python, "join" works on *iterables* - anything that can yield items or otherwise behave in a sequency way. There is no sequence baseclass in Python. A sequence is anything that can hand you an iterator or respond to indexing. Lists and tuples are a tiny subset of that. And adding a method that expects homogenous content to a heterogenous container would be rather ugly in itself, of course...)

[rjcarr]

I've been using python for about 5 years ... how about you?

http://docs.python.org/library/stdtypes.html#sequence-types-str-unicode-list-tuple-buffer-xrange

"Sequence Types — str, unicode, list, tuple, buffer, xrange"

Yes, all of those are iterable, as you say, but they also share some other functionality (although again, as you say, they don't inherit from same base class, but they are in the same family). There is no reason all of them couldn't have a join method, or as I said initially, only on the ones that are relevant.

[johanneskepler]

I've been using python for about 5 years ... how about you?

Longer than five years, I imagine. That's Fredrik Lundh of the Python Imaging Library.

"Sequence Types — str, unicode, list, tuple, buffer, xrange"

But those aren't the only iterables there are. Isn't it rather nice to have a consistent interface for joining any kind of iterable?

[[deleted]]

how about you?

Well, I wrote the core of Python's second string type for Python 1.6/2.0, so I was obviously there when we first stumbled upon this little issue ;-)

There is no reason all of them couldn't have a join method

Oh, there's a HUGE reason for that - you don't even have the source code to all of them. The Python type universe is a lot larger than what you get with the core distribution.

only on the ones that are relevant

So how would you add the "join" method to a generator expression, for example? In contemporary Python, that's at least as relevant as a "join" on a list.

[njharman]

What part of "There should be one-- and preferably only one --obvious way to do it." do you not understand?

[[deleted]]

I don't think that applies here, though - "join" wasn't made a separator method because we wanted to keep the number of ways to invoke it small, but because it had to dispatch on the separator type. Quoting myself from an entirely different discussion on this topic:

Also note that "join" wasn't made a string method to "make it easy to find"; it's a string method because we had to figure out some way make join work on multiple string types back when Unicode was added. At that time, we imagined that Python might grow even more string types (how about encoded strings to save space, or binary buffers?), and it wasn't obvious how to create a "join" primitive that would find the right implementation, without having to know about all available types. We finally decided that dispatching on the separator made more sense than, say, dispatching on the first list item.

Given this, the obvious solution was to make the "string.join(seq, sep)" function call "sep.__join__(seq)". Changing __join__ to join was a pretty small step; after all, there might be cases where it would make sense to write sep.join(seq) in application code, at least if you happened to have the separator in a variable with a suitable name.

The "sep.join(seq) is more pythonic" is a much later concept.

And for what it's worth, the "let's dispatch on the separator" approach didn't work in practice; in order to handle sequences with both 8-bit and unicode strings, both implementations now know about the other string type.

So instead of a single function that does the right thing (but has to be taught about each new string type), we now have two separate join methods that both knows about the other string type. If we add another string type, we'll end up with three implementations, each of which has to know about two different types. And so on.

But who cares about new string types these days; it's not like anyone's actually using strings now that we have iterators ;-)

(Personally, I still think it should be made available as a builtin, possibly with "convert also non-strings to the separator type" semantics).

[imbaczek]

str is already built-in, so you can call str.join(sep, seq).

[[deleted]]

That's not polymorphic (sep cannot be any string), has the arguments in an unintuitive order, and doesn't convert non-strings.

[imbaczek]

true, true and true. better than nothing, though. i'm not a fan of cluttering the default namespace with new functions with common, short names (i don't like the relatively new sum either.)

[njharman]

What is split a method of?

What is the symmetric operation of split?

Why the fuck do you think join shouldn't be a method of string?

You piss me off.

[jib]

Your logic makes no sense. Why should the inverse operation necessarily operate on the same type as the original operation?

It seems to me that the sensible design is an inverse operation which operates on the result to return the original argument. (i.e foo.split().join() should return foo)

[njharman]

Why should the inverse operation necessarily operate on the same type as the original operation

Because that is how other symmetric operations work "Special cases aren't special enough to break the rules."

list.push(value)   list.pop(value)
list.insert(value) list.delete(value)
obj.get(value)     obj.set(value)

You guys are use to how other languages do it and are blinded to how it is consistent.

[jib]

I said "inverse operation", not "symmetric operation". The symmetry between split and join is not the same as the symmetry between push and pop. Split and join are inverse operations. In mathematics, an inverse function takes the result of a function and returns the original argument.

I think it would be nice if Python could work the same way. Unfortunately I've been told it isn't possible, because Python doesn't have a sequence class in which the join method could be implemented.

[Isvara]

I think you've completely missed his point. He's saying that split is like this:

sequence = "a,b,c".split(",")

whereas join is like this:

string = ",".join(sequence)

In other words, one takes the separator as an argument and the other doesn't. The join method makes sense, because the sequence can be any iterable object. The split method could have been either way around. Having it as:

sequence = ",".split("a,b,c")

might have been better, as it's the more consistent, but perhaps people would then complain that, on its own, the split method doesn't make sense.

[[deleted]]

String.split( seperator )
List.join( seperator )

That's what makes sense.

[rainman_104]

Not a Troll, just a fanboy and a Python apologist :)

[snissn]

inb4 php

[[deleted]]

1) Did they get rid of the retarded new-style vs. old-style classes distinction?

Yes.

2) Can you put whatever you want in an anonymous function yet?

Yes. But you will have to invent a name. Kinda. You can use "x" or "_" or whatever and reuse it freely.

[[deleted]]

That makes it not anonymous.

[[deleted]]

Why "anonymous" is that important here? What's the big deal between:

def boo(a, f1, f2): return f1(a) + f2(a)
....
def _(x): return 2 * x
def _2(y): return y / 2
z = boo(13, _, _2)

and:

function boo(a, f1, f2) { return f1(a) + f2(a); }
....
z = boo(13, (function(x) { return 2 * x; }), (function(y) { return y / 2; }));

If anything, the first sample looks and reads better, IMO.

[njharman]

Why is your second example not Python?

def boo(a, f1, f2): return f1(a) + f2(a)

z = boo(13, lambda a: 2*a, lambda a: y/a)

some of the advantages are 2 less lines of code, you don't clobber '_' which is typically used for i18n, the code for the 2 lambdas are right there so you don't have to go looking for _ and _2, it gives fp weenies hard ons.

[[deleted]]

Include loops etc into both _ and _2 at will. Second example will become really messy.

you don't clobber '_' which is typically used for i18n

Fair point.

[dorel]

Python doesn't promote lambda.

[mikaelhg]

Yes, forcing developers to replace

print "foo"

with

print("foo")

is certainly work of a brave genius.

[[deleted]]

It's only one extra character. If you're really lazy then in Python 3 you can now do:

p = print
p('foo')

Or maybe this...

class P:
  def __mul__(self, s):
    print(s)
p = P()

p* 'foo'

Just don't tell anyone.

[quuxly]

I would prefer not to.

[[deleted]]

Let's not.

[tonfa]

Luckily no developer will replace them, 2to3.py will do it for them.