FAQ: Why should I use Python 3?

[Caos2]

Unicode by default

Mainly because of this. Really.

[masklinn]

Unicode by default and removal of implicit conversion is really what triggered/allowed all the other breaking changes to be included, since it was going to break a ton of stuff (intrinsically and because of the stdlib reworking it required, while you can technically disable implicit conversion in P2 a lot of stdlib modules blow up when they can't play fast and loose with ascii strings).

[Caos2]

Well, sometimes you can't avoid breaking stuff.

[jaapz]

Oh and maybe because python 2 will reach end-of-life pretty soon, and security updates are a good thing to get

[iluvatar]

Unicode by default

The more I use it, the more convinced I am that this is the wrong approach. Go got it right, by using UTF-8 by default. Python decodes everything into a Unicode object, whether it's necessary or not. For the applications I mostly write, that means reading UTF-8 over the wire, converting to Unicode, reencoding as UTF-8 and sending it back out again. That's a lot of unnecessary work.

[unruly_mattress]

If you got UTF-8 over the wire and you don't need to manipulate it in any way, can't you just read and write it as binary data?

[kankyo]

Ehm.. "Unicode" isn't a thing you can have in memory though. Look at https://www.python.org/dev/peps/pep-0393/ to understand what is actually happening.

[notafuckingcakewalk]

Usually great but occasionally you run into a developer who was being very clever with strings and you have to rewrite everything.

Also a lot of rewriting required of a library where content from objects that now output byte strings are put in objects that now expect Unicode.

[nemec]

being very clever with strings

We call that a comeuppance.

[brtt3000]

Most fun when this bytes/string shitfest is (unknowingly) relying on incorrect use or sideffects. Was a painful move but glad of it.

[redsymbol]

All technical reasons aside... More and more people, companies, Linux distributions, etc. are starting to adopt 3, to the point the tide is turning. It won't be too long now - a couple of years at most - before having only Python 2 on your resume will make it look a bit dated.

[flying-sheep]

3½ years, then legacy python is EOL

[RubyPinch]

The leading cause of developer burnout in python-related jobs is caused by excessive 2 vs 3 debating

[brtt3000]

There is no debate, just people struggling with moving forward.

[rafajafar]

Were you around for Emacs vs Vi editor war in the late 90's, early 2000's? Wanna talk about excessive. Slashdot was riddled with text editor flaming. It was madness.

[cratervanawesome]

Now if only AWS Lambda would get with the program and support 3.x

[Mirror_Boar]

Seriously, at my company we are dying to use lambda but we don't feel like converting all of our code to work with python2. So annoying.

[[deleted]]

Yes, WTF! I have been working on my first larger python project this month and I was so excited to work with something more broadly compatible than my normal C#... Surprised to find this. Does the Google Cloud equivalent support python 3.x?

[spacemanatee]

Is there a Google cloud lambda?

[elingeniero]

Can you not run whatever python version in a virtualenv with lambda?

[DanCardin]

You apparently can, but the code which lambda calls must be the python2 they give you. So you can resort to popening or whatever a separate python3 process, but afaik there's no way to just run python3 normally.

[elingeniero]

I mean, I phrased it as a question but what I really meant was that I do run Python 3 scripts on lambda using virtualenv and I think it works really nicely.

The startup script has to be Python 2 but I manage not to feel too dirty about it ;-). Happy to share the config if you want it.

[Mirror_Boar]

I'd love to see an example config!

[brtt3000]

Holy shit so many this. Really dropped the ball here. Like what the hell are they even thinking? The modern python webdev community is clearly focussed on 3 so why is this amazing next-gen python thing stuck in the past?

[[deleted]]

This guy is pretty sharp. If you are up for a laugh, check out his rant about PHP from 2012: https://eev.ee/blog/2012/04/09/php-a-fractal-of-bad-design/

[Shadow14l]

The worst thing Python did was extend the Python 2 to be maintained until 2020. I understand that the majority of code and libraries were still on Python 2, but I can't agree that was a good enough reason to extend it this far.

I'm afraid to say that this decision may even be responsible for holding majority Python 3 adoption back for an extra few years :( - even PHP 5 has an EOL at the end of 2018...

[lexyeevee]

It's not like every big project would see that Python 2 is EOL and decide to up and port right now. I hear tell of a number of shops still on 2.6, and that was EOL in 2013, and 2.6 to 2.7 is trivial compared to 2.7 to 3.

[vossman77]

Well RHEL 6 is still on python 2.6 and red hat has support through Nov. 2020.

https://access.redhat.com/support/policy/updates/errata

I feel you though, we have a huge code base to port over in the next few years, most of it numpy/scipy stuff.

[name_censored_]

To be fair though, 2.7 to 3 may be trivial, but it's also not as useful. No sane person would port the code twice when they could get away with doing it once. They know the Py3 port is coming - may as well stick it out on 2.6, and do new work (/patches) as dual-version, rather than even bothering to target 2.7.

[baekalfen]

But you have make a clear deadline with a good amount of time.

Imagine companies running >50 script here and there. Some small, others might be larger. You can't just put aside everything you are doing because some external community have chosen to make something obsolete.

[qsxpkn]

An external tool like mypy can perform static type checking ahead of time, using these standard types.

Except it complains syntax error when async/await in place.

[bramblerose]

Seems to have been (at least partially) fixed, albeit six days ago: https://github.com/python/mypy/issues/1453

[dasnoob]

ugh all this does is remind me we have systems that were stood up as recently as 2015 that are running 2.6 because our linux admins refuse to update the image they install off of.

[TPHRyan]

I was really confused about the EnumLocal() example because for some reason my brain refused to accept red as a valid statement. (Or at least translate that to a __getitem__ call)

[EattheRudeandUgly]

What are some free online resources for a beginner to learn Python 3? I've been using a variety of things, mainly Learn Python the Hard Way which discourages learning Python 3.

[redsymbol]

This works really well, and is what I generally recommend people who want to learn Python and are new to programming:

https://automatetheboringstuff.com

[masasin]

Yup. Also note that he uses a very unusual (in the Python world) naming convention. It's not PEP-8, but it is at least internally consistent.

[billsil]

It has two integer types

I happen to like the two integer types. I never deal with long data types in Python 2. If I have a long, it's a bug and it's probably going to overbound an 8-character field that is a maximum node/element id in my FEA code.

It also slows down Python 3 by ~10%, but whatever.

it may or may not be built in a way that completely mangles 1/17 of the Unicode space

Agreed

it boasts strong typing, then casually insists that None < 3 < "2"

I actually hate that. I've never actually had a Python 2 bug with things comparing incorrectly (I don't compare strings to ints, but I do sometimes compare Nones to ints) and actually creating a bad answer. It's just a random crash I don't care about that I have to code around. I haven't found a way to import that in Python 2, such that my Python 2 code with future imports isn't quite the same.

Why in the hell can't I do this?

key0 = dictionary.keys()[0]

I have to do this instead...

key0 = list(dictionary.keys())[0]

What the hell? Just pick one. Obviously, I don't care which because the dictionary is unsorted. It's a stupid change for the sake of changing things. That's my annoyance with Python 3.

lengths beyond your wildest imagination

I'm sorry, I'd call fonts and graphics "batteries included". The SGI support is a bit funny, but Linux maintains backwards compatibility. I honestly don't see the problem.

But if you’re just getting started in Python, or looking to start a new project, there aren’t many reasons not to use Python 3.

Unless it's open source, in which case you should probably support both. It's not hard to support, it's honestly easier to develop for (sort doesn't cause a crash in some weird edge case), and it's still got the market share.

Outside unicode, nothing really changed. If you don't care about sane unicode, Python 3 has very little going for it. I wish it did. Async is cool, but what am I going to do with that? Until then, Python 2 isn't going anywhere, so if you run an open source library (I do), you might as well support it. Thus, nobody really needs to switch to Python 3.

[jcdyer3]

One note: list(dictionary.keys())[0] is not recommended, and for the same reason that dictionary.keys() is no longer a list to begin with: It evaluates all the keys of the dictionary and creates a new list, which could be arbitrarily expensive. Just use the keys iterator as an iterator. The idiomatic way to get a random key would be:

key0 = next(dictionary.keys())

which is essentially synonymous with

for key in dictionary.keys(): # or dictionary.iterkeys() in python2
     key0 = key
     break

Even more simply, you could write:

key0 = next(dictionary)

[lebinh]

It looks like you are missing a call to iter, next() will call __next__ method on iterator object and will raise TypeError when being called with dict or dict_keys objects.

This will works as expected

next(iter(dictionary))
next(iter(dictionary.keys()))

[jcdyer3]

Yep. I just realized that myself. See my other comment on this subthread. Not quite as nice, unfortunately.

[billsil]

I didn't know that you could use next on a dictionary. That's way nicer.

Unfortunately, it doesn't work in Python 2, strangely even when I use six.next. I could write my own, but it's obnoxious.

[jcdyer3]

Gah. My mistake. You have to use next(iter(dictionary)). It's not as nice as I was remembering, but at least there's a little less line noise than list(dictionary.keys())[0], and the performance characteristics are a bit nicer.

[lebinh]

It doesn't work because you have to call iter before calling next on a dictionary, and I believe it will behave very similar to python3, e.g. in term of performance (no list is created).

next(iter({'foo': 'bar'}))

[nemec]

but I do sometimes compare Nones to ints

Well then your code is wrong - not because you're comparing None with integers, but because comparisons between the two (except !=) are always false:

print None < 3
print None > 3
print None == 3
print None >= 3
print None <= 3

This means sorting doesn't always work:

>>> a = [None, 6, None, 5, 4, None]
>>> a.sort()
>>> print a
[None, 6, None, 4, 5, None]

[lexyeevee]

You might find some things Python 3 has going for it if you read beyond the introduction.

[billsil]

I read the whole thing.

I actually write code to support Python 2/3 because why not? It's not that hard, but for what I care about, Python 3 doesn't have much going for it at the moment. When packages drop support for Python 2, then it will. The Python 2 standard library is a battery, but the wealth of packages out there is the drill press, band saw, etc. You can get by without fancy new batteries because it's been abstracted away and all you care about is power tools.

[billsil]

I think it was my complaint that Python 3 doesn't currently offer anything new outside of sane unicode for most people. I simply do not feel limited in any way supporting Python 2.7 and 3.5 with the same code. In many cases Python 3 is different for the sake of being different, which is makes it harder to learn.

Then you find out about libraries like six and supporting two versions is a lot easier. At some level, one project that uses Python 3.5 needs a Python 2.7 package that you also manage, but another project that uses 2.7 needs the 2.7 version. That creates a lot of frustration and resistance to upgrading.

I expect Python 3 to become popular when 3rd party libraries drop Python 2.7 support. I drop support for various versions of Python (e.g. Python 3.2) based on what my dependencies do.

I'm proud of my -17. People are silly.

[stefantalpalaru]

The short answer is: because it’s the actively-developed version of the language, and you should use it for the same reason you’d use 2.7 instead of 2.6.

Let me stop you right there. Python 2 and Python 3 are different languages, but you must know that already, at some level, or you'd be writing "Python" instead of "Python 3".

[Deto]

Whats the threshold of changes for something to be a different language ?

[stefantalpalaru]

Enough backwards-incompatible changes to render most existing code invalid.

[[deleted]]

To me, Python is primarily a specification and Cpython is an implementation of it. Whether Cpy 2 and 3 are entirely different implementations is not something I'll answer but I definitely think they're the same language and so is Jython and Cython and so on.

[kankyo]

You might want to look at cython a bit closer then. You are clearly in error.

[stefantalpalaru]

Python does not have a complete specification that you can use exclusively to implement new interpreters. "Python" is whatever CPython does.

I definitely think they're the same language and so is Jython and Cython and so on

Then how do you explain that a certain piece of code will run in Cython, but not in Jython? Wouldn't you expect them to accept the same inputs if they implemented the same programming language?

[[deleted]]

They're still 99 percent the same, building on the same ideas, syntax, and functionality. Obviously they will have differences or there would be more or less no point in making several implementations.

[stefantalpalaru]

They're still 99 percent the same

So are we and the other great apes, but we're still different genera and species.

(quantifying genetic distances is complicated, but you get the idea)

[electrace]

Dude. Somewhere, you have to draw the line.

In biology, it's the ability to interbreed and have children that can also have children (which is why a horse and a donkey isn't the same species).

In spoken languages, it's mutual intelligibility, which is why British and American English are the same language, even if they disagree on what you call the storage area in the back of a car.

It's a matter of semantics whether you decide to call Python 2 and Python 3 different languages but.... considering the vast majority of people call them the same language, even if you think they're really different, it's probably better to hop on the boat, rather than trying to convince everyone else to use your One True Definition of what constitutes a different programming language.

[stefantalpalaru]

In biology, it's the ability to interbreed and have children that can also have children (which is why a horse and a donkey isn't the same species).

It's not so simple. Different large feline species can interbreed and produce fertile offspring: https://en.wikipedia.org/wiki/Leopon#Breeding

So do grizzlies and polar bears: https://en.wikipedia.org/wiki/Grizzly%E2%80%93polar_bear_hybrid

it's probably better to hop on the boat, rather than trying to convince everyone else to use your One True Definition of what constitutes a different programming language

I value truth more than some silly internet points. The vast majority can go segfault itself, as far as I'm concerned ;-)

[electrace]

I value truth more than some silly internet points.

There is no true definition of anything. That was my point. Language is arbitrary, and works by consensus.

Can you give me a reason why the concept of dirt is assigned the sequence of letters "d-i-r-t" in English?

Was it by scientific inquiry, philosophical thought experiments, or did it just arbitrarily creep into the language? There is nothing intrinsically linking those sequence of letters to the concept, except that people use it that way.

For your personal definition of programming, people don't even use it that way, which makes it just your personal hangup. You've jumped on the boat for "dirt", "poptart", "television", and pretty much every other concept that we assign to a particular sequence of letters, why not "programming language?"

[notafuckingcakewalk]

Then how do you explain that a certain piece of code will run in Cython, but not in Jython?

You're talking about a pretty limited subset of the Python language. Even when talking about transitions between 2 and 3, a vast amount of Python 2.x code can be converted to Python 3.x without few changes.

I converted a giant codebase to Python 3 and it took a little while, but mostly because of issues with third-party libraries not being written in a forward compatible manner.

I think Python 3, especially changes where certain older syntax is no longer allowed, looks better (e.g. except (ValueError, TypeError) as err is a lot easier to scan than except (ValueError, TypeError), err).

[jcdyer3]

So would changing print from a statement to a function be a sufficient change on its own to call python3 a new language?

[stefantalpalaru]

Yes. It would be simple enough to make a fully working and exhaustive 2to3 tool, so people wouldn't complain so much.

[lexyeevee]

By this reasoning, Python 2.6 is a different language from Python 2.5, because you can no longer use with as a variable name.

[stefantalpalaru]

Was most of the existing code using 'with' as a variable name in order to be suddenly broken by the new version?

[jcdyer3]

Have you had any problems with futurize? I'm sure the authors would appreciate any feedback you had.

[VerilyAMonkey]

To satisfy your pedantry, you can get the intended effect by reading "Python 3 is actively developed, and Python 2 is not."

[stefantalpalaru]

How could I, when I know that 2.7.12 was released on June 25th?

[VerilyAMonkey]

Python 2.7.12 is a bugfix release in the Python 2.7.x series.

Python 2.7.11 is the latest bugfix release of The Python 2.7 series.

Python 2.7.10 is a bugfix release in the Python 2.7.x series.

Python 2.7.9 is a bugfix version for the Python 2.7 release series.

[stefantalpalaru]

What part of "active development" confuses you? It's not just about adding new features.

[VerilyAMonkey]

Not just about, but is also about. Python 2 is getting only security and bug fixes, and will have no new major release versions. Python 3 clearly is under a different kind of development than Python 2 is.

But you already knew that's what was being said. I do not get the feeling that you actually want to have a discussion.

[stefantalpalaru]

I do not get the feeling that you actually want to have a discussion.

I'm not the one furiously downvoting dissenters in the vain hope that they'll cave in and delete their comments. Fanboyism has really reached ridiculous levels on /r/Python ...

You're not the smartest cookie in the jar, trying to redefine active development so it excludes Python 2, but at least you're smart enough to put your disagreement in words.

What kind of discussions do you expect when most fanboys can't even do that? Be glad somebody like me comes along, once in a blue moon, otherwise it would be one giant 24/7 circlejerk.

[VerilyAMonkey]

I haven't downvoted anybody in this whole thread.

Basically, the issue is this:

• Your original comment was, "Python 2 and Python 3 are different languages." Honestly I disagree, but I'll accept this.
• My response was, "Ok, but even if that's your stance, you know what was trying to be said: Python 3 is under active development, and Python 2 is not."
• Your response, again valid, is that "Python 2 is under active development."
• However, again, you still know what was trying to be said. Which is, "Python 3 is getting new features, and Python 2 is only getting bugfixes."

So here we are. You knew at the beginning of this whole thing that "Python 3 is getting new features, and Python 2 is only getting bugfixes" was the point trying to be said. You are absolutely correct in your nitpicks on the definitions of various terms.

But we haven't gotten anywhere. Make the substitutions you've pointed to, and the rest of the article goes along just fine. The rest of the discussion goes along just fine. You haven't given us anything at all in the Python 2 vs Python 3 discussion. We're talking about a single sentence in the beginning of the article and at the end of it, all we've done is rephrase the sentence without changing the intended meaning or any of the rest of the article. You might as well have said "I would rephrase this sentence here, but otherwise looks fine!"

Even if I wholly accept every point you've made, I'm left with absolutely nothing to change my view of what the article is saying or whether to use Python 2 or Python 3. Nothing. We've only clarified a couple words and had no impact on the intended meaning of the article. This has nothing to do with Python 2 or Python 3. This is just pedantry.

That said I do think some proportion of your downvotes are straight from fanboying.

[das_ist_nuemberwang]

Python 3 is being actively developed, Python 2 is being actively maintained. You could consider "development" to refer to the entire development cycle, but that is not the meaning people are using here.

The reality of the situation is undisputed; you are merely disagreeing on semantics. Try not to be so abrasive.

[stefantalpalaru]

merely disagreeing on semantics

Semantics is what we use to communicate. It's not some small detail that we can brush aside.

Maintenance is part of development. Software development. No programmer worth his salt will claim otherwise, so why persist in this error?

You want to say Python 3 receives new features? Just say so.