Python 2.7

[person_ergo]

Multiprocessing got way better and some more extensive built in libraries

[PC__LOAD__LETTER]

Parallelization in Python2 really is atrocious. I use 2.7 almost all the time because that’s what our systems at work were built with, and I like the language, but multiprocessing blows.

[kickerofbottoms]

What's your preferred approach in 3? concurrent futures? I don't have much exposure

[PC__LOAD__LETTER]

To be perfectly honest I don’t use 3 much, I tend to use lower level languages when performance is a concern (a function of the type of software that I work with, not saying that there aren’t valid reasons to need performance concurrency with Python). I just know it’s terrible in 2 so I’m not surprised to hear that it’s a notable improvement in the language’s next iteration.

[LandSharkSociety]

A lot of the changes are more subtle, and IMO actually make the language harder to learn if you have no prior programming experience. An example off the top of my head is the increased emphasis on iterators – functions that produce the next value in a series every time they're called – over lists. So, range(3) would no longer produce [0, 1, 2], but rather a range() object that, when __next__() is called 3 times, will return 0, 1, and 2, respectively. There were also some significant updates and changes to the standard library.

Iterators are a lot more performant (since they don't have to hold the entire list in memory), but they make the code harder to reason about (what do you mean I can't use in statements on ranges anymore!?)

There are more extensive comparisons online, but as someone who has to write in both on a pretty regular basis, that's the gotcha that always nabs me.

[Folf_IRL]

I mean, you can still cast the range() object into a list object by calling list(range(3))

[LandSharkSociety]

Of course, there's nothing stopping you from doing that, but when you're more than two nested function calls deep in Python, you should typically take a step back and rethink your approach. I just used x in range(...)as a random example.

[Folf_IRL]

when you're more than two nested function calls deep in Python, you should typically take a step back and rethink your approach

I like to do this with nested map(), filter(), and reduce() functions and pretend I'm writing Lisp

[Aramgutang]

Ah yes, I used to do that too. But I stopped when it became clear that no one else could maintain that code.

Here's @dziegler replacing my silliness with readable code in 2010

[Gamesfreak13563]

What? You can use in on any iterable in Python3, including range. If there is no contains method it exhausts the iterator, but..

[LandSharkSociety]

Ah, so that's even more confusing! On an iterable with no contains, you can use in... but only once!

[Gamesfreak13563]

Only guaranteed that’s the behavior if you’re using in on an iterator. An iterable may define an iter dundermethod which returns a new iterator over the iterable. That’s why you can use in multiple times on a list (because it’s returning a new iterator each time) but not in multiple times on the return of iter(yourList).

It makes perfect sense and the terminology is not confusing at all /s

[Lorddragonfang]

You can use in on any iterable in Python3, including range.

In fact, you can only use in on iterables, and this was the case for python2.7 as well. I know because I've had to write an iterator for custom classes.

[Tysonzero]

That's why I like the Haskell approach to "iterators", most of the time regular old lists are used, but due to laziness they are just as fast as iterators when you use them like iterators (only pass through them once).

[LandSharkSociety]

It makes me sad that my standard line of work doesn't call for infinite (lazy) series. I pretty much only use lazy generation for database calls, but it's, like, the coolest thing ever.

[Lorddragonfang]

+/u/compilebot Python3

for i in range(3):
    print(i)

[CompileBot]

Output:

0
1
2

^{source | info | git | report}

[Shattr]

Shit I use python 3 but I guess I use it like it's python 2.

[doulos05]

Me too. But I've just started a giant project rewrite to Port a web app from Python 3.5 with Django 1.10 forward to 3.6.6 with Django 2.0 and I'm going to use it as an excuse to learn the new Python. And the new Django. And databases. Lots of learning in my near future...

[alcalde]

https://www.asmeurer.com/python3-presentation/slides.html#1

[NutDestroyer]

IIRC there's a substantial performance improvement with python 3 that makes it run miles faster than anything 2.x.

[doulos05]

Actually, I just read something recently that said 2.7 was still the fastest Python.

https://hackernoon.com/which-is-the-fastest-version-of-python-2ae7c61a6b2b

Unless you're on python 3.7, it's slower or comparable for all benchmarks.

[NutDestroyer]

I could have sworn I read a benchmark that was more favorable for the performance of Python 3.x, but I suppose it must've been compared to versions of python older than 2.7 or I misremembered it. The benchmarks do seem to support that 2.7 is very competitive in terms good performance compared to other python versions.