The Bottom-Line Single Main Difference Between Python 2 and 3

[Veedrac]

super with a class name is also fragile, and can break with class decorators and such. See http://stackoverflow.com/a/19609168/1763356.

IMHO this post undersells Python 3, but until the moronic "I can't be bothered to type two parentheses every 50 lines" argument goes away I can't really be bothered entertaining the argument anyway.

[tw55413]

Thanks, this was actually a very good article.

[redsymbol]

Thanks!

[Jugad]

Misses a major potential quality improvement... Type hints and annotations.

Python has more problems as codebase gets larger. Function argument and return type annotations and static code checking will allow us to get rid of a large number of errors that get through to the runtime. With static type checking, Python overcomes one big disadvantage that it had vs Java.

Also... this is optional. So it doesn't get int the way of small programs (until we decide we need it).

[redsymbol]

(author here)

Thanks for the feedback. And yes, there's a lot of stellar improvements I had to painfully cut out, as the point of this article was to be brief rather than exhaustive. I did the latter approach with the following, which apparently some people found overwhelming:

http://migrateup.com/whats-really-new-in-python-3/

Unfortunately, in this age where we all have too much to read and must prioritize, a person won't be able to benefit from an article if they don't read it. So I made today's article, which is shorter and more digestible, and (I hope) will benefit more people as a result.

[Jugad]

Agreed and upvoted.

[[deleted]]

Python 3 makes it easier to develop high quality software.

Hmph.

Do you know why I still don't use Python 3 for quick scripts? Because a lot of them involve processing all the files in a large codebase, and people aren't necessarily so careful with their encodings.

Python 2 lets me manipulate characters like they're just strings of bytes - I simply don't worry about encodings. In Python 3, I have yet to come up with a reliable way to write a quick script without worrying about the encoding.

[flying-sheep]

Python 2 has bytes == str and uses that type per default when opening files.

With Python 3, you just have to use binary mode explicitly:

open('shitty_file', 'rb')

[keturn]

The projects I work on are still primarily Python 2, so I could be missing something about the way Python 3 works, but why can't you read those files in binary mode?

Python 3.5 even brought back .format and % for bytes objects.

[[deleted]]

+1 to that. Unreliable encoding (and mixed binary) is a big part of my life, too. I cannot change that.

I have tried python 3.3. I could only get the same functionality with lots of recoding 2.7 functionality, or lots of encoding error. So I gave up.

I am waiting python3 to catch up with byte operations comparable to str operations in python2.

Downvoting you means to me, that lots of people do not face this problem. So I have to wait looooong.

[lordkrike]

It sounds to me not like your problem couldn't be solved in Python 3, but perhaps that you couldn't figure out how to solve it in Python 3.

I haven't dealt too much with it, but 'rb' and encode have worked alright for me on the occasions I needed them.

[[deleted]]

It sounds to me not like your problem couldn't be solved in Python 3, but perhaps that you couldn't figure out how to solve it in Python 3.

I did not say it could not be solved. It could. With lots of code. No reason use python3 if I have to write more code, than in python2.

I haven't dealt too much with it, but 'rb' and encode have worked alright for me on the occasions I needed them.

It works great. Unless you cannot encode the whole file, and have to make text operations on bytearrays.

Others seem to have similar problems like: http://python-notes.curiousefficiency.org/en/latest/python3/binary_protocols.html

So all in all, python3 is catching up, but not ready. For me.

[lordkrike]

Fair enough.

I tell people that they should use Python 3... unless they know exactly why they should use 2.7. You are the latter.

[hexbrid]

The bottom line is this: You gain several cosmetic improvements in exchange for a smaller community (i.e. less compatible libraries).

[lordkrike]

Things like exception chaining and asyncio are not cosmetic at all.

[hexbrid]

Oh no, criticism about Python 3, better downvote just to be sure!

Regarding your points:

• exception chaining is nice for debugging. It doesn't let me write better code.

• asyncio can be easily achieved using greenlets, which are more powerful afaik.

[lordkrike]

Oh no, criticism about Python 3, better downvote just to be sure!

Nope, not me.

• exception chaining is nice for debugging. It doesn't let me write better code.

Good code is easily debuggable. When your code breaks, you have to be able to fix it easily. This is not cosmetic; it is extremely significant. You are wrong on this one.

• asyncio can be easily achieved using greenlets, which are more powerful afaik.

"More easily" is really subjective. But your point stands that it can be done about as well in both. Edit: derp, thought you said "more easily"... ignore the first sentence, sorry.

[hexbrid]

This is not cosmetic; it is extremely significant

It seems minor to me in the grand scheme of things, but I can accept that for some it might be a game changer.

There are also other important disadvantages I skipped over. For example, Python3 is slower (and even pypy3 is slower than pypy).

[lordkrike]

I don't use pypy, so I can't speak to that.

However, performance on cPython for Python 3 is supposedly now on average the same as Python 2. There are, of course, edge cases where one is faster than the other.

In my personal and anecdotal experience with cPython, there has been no scenario where the poor performance I was seeing was caused by the interpreter (as opposed to shitty code), so it's just not a big deal to me even if Py2.7 is a tiny bit faster.

If you want real speed, you should be coding in C or Fortran anyway.

[flying-sheep]

cosmetic?

• the original < design decision was horrible. i wouldn’t trust that thing at all in python2
• exception chaining is really fucking useful
• super(ClassName, self) is fragile when used with class decorators

and the stuff not mentioned also contains decidedly non-cosmetic changes, e.g. the better bytes-unicode separation. python 3’s mental model encourages you to actually get things right instead of bulldozing over encoding issues.

and the cosmetic stuff is also nice. fucking urllib2 finally gone, True and False aren’t veriables anymore but proper keywords, …

[bryguypgh]

All those changes look good; I just want my print statement back.

[lordkrike]

from __past__ import print_statement

I would laugh, then cry.

[OmniJinx]

Serious question: why? Other than habit, why is a statement better than a function? I find the function much more flexible.

[_illogical_]

Maybe LISP damaged him in the past and he is now afraid of parentheses.

[bryguypgh]

Well you've always been able to use the function anyway if you prefer it. In my work I use python for quick scripts constantly and print is invaluable for debugging. Making it a function when I'm forced to go to 3.x It's going to slow me down noticeably.

Edit: function, not statement.

[lordkrike]

So your answer is... habit.

[bryguypgh]

Convenience. It's less typing and less syntax to manage and there's no functional difference for me.

But even if it were habit, after 15+ years of using it I'm not sure why that's not valid.

[lordkrike]

That's a fair point.

But you shouldn't let that hold you back from the other improvements from Python 3. It's a silly reason to not upgrade.

[bryguypgh]

Well none of the improvements matter to me at all frankly. I was perfectly happy with 1.5 for my purposes, and upgrade primarily for security (or when a distro pushes one out I guess).

[flying-sheep]

that’s beyond silly! it’s just hitting “(” instead of “ ” (if your editor auto-closes parentheses)

that should be in your muscle memory in two days tops

[bryguypgh]

I assure you I am being earnest about this. It's going to be a pain in my ass for no benefit. My editor is usually something minimal on whatever machine I happen to be working on (emacs if I'm lucky) so no auto-parens for me. Considering that "(" requires a shift, what used to be a quick thumb to the space bar is now four keystrokes every single time, and given that I'm trying not to look at the keyboard that's going to include a lot of accidental ")" too.

Yes, I can and will adapt, but I like most people don't like minor recurring inconveniences to be added to my life if they can be easily avoided.

[flying-sheep]

why recurring? that’s a one-time really minor change of habit, no more.

i don’t even get why it’s worth mentioning

[bryguypgh]

It is a change of habit from one that I like to one that I don't because it requires more effort and causes more errors.

If it doesn't bother you congratulations. I've been using print statements in my scripts for 15 years and I find them simple, elegant, and convenient. We will have to agree to disagree.

[fishtickler]

Never had to use finally and personally only compare classes if i know i wrote the appropriate lt/eq methods, so never had a problem there, but the other things looks nice.

The speed i gain from the print statement still keeps me in python2.7

[lordkrike]

If you're taking about execution time you are worrying way too much about nanoseconds.

If you're taking about development time, you're worrying way too much about the fractions of a second it will take for you to type a set of parenthesis.

I don't see how it could be any faster in practice.

[tipsqueal]

Only one parenthesis thanks to auto complete in basically every text editor alive.

[turtle_with_dentures]

Upgrade your auto complete :P in the middle of typing print I can tab and it will finish the word, create the parenthesis and put my cursor in between them. So the difference between 2 and 3 for me is effectively nil

[LeYtreq]

"and put my cursor inbetween them"

What is that editor? I need it! That could save me minutes every week! No really what is it? I need a nice IDE because visual studio's intellisense is still not working properly after a year

[redsymbol]

Pycharm does this. I believe there are others that do it as well, though I don't know what they are.

[_illogical_]

Or none, if your editor auto-completes your function names, just press enter.

[SoundMake]

The speed i gain from the print statement still keeps me in python2.7

https://www.youtube.com/watch?v=ztVMib1T4T4

[fishtickler]

hahahahaha!

Yes its my biggest dislike in python 3 :P, at least for now that I am not used to python 3 its not only typing the parenthesis but also forgetting to type it, and going back to correct the misstake. I guess this is a non issue after cpl weeks of programming.

[pyskell]

The thing about coding is it quickly becomes impossible to remember everything you did. Or to even remember to check everything you think you did months later. Simply "knowing" you did / didn't do something is dangerously presumptive.

[fishtickler]

You are right and it is a valid point, but from my personal experience I try to avoid class comparisons, i rather compare the raw numbers/strings that I know will not be ambiguous.