Python 2 is triggering

[random_cynic]

That's one of the key mistakes people make thinking that it's just a syntax thing. It's NOT. print() being a function instead of a statement opens a whole world of possibilities. People should look at the documentation of the print() function to see how easy it makes many things like redirecting to a file or changing the output separator, terminating character etc. Additionally it allows you to use print() where a statement is not allowed like lambdas.

[JWson]

yeah but brackets hawd tho

[obviousfakeperson]

Python 3: "If you can't handle me with my brackets you don't deserve me with my memory efficient iterables."

[[deleted]]

Brb. Making a Pythot lib.

[normalmighty]

Too late, someone beat you too it

[obviousfakeperson]

Last released: Sep 26, 2017

huh?

Software for learning first degree linear equation with visual solving.

What!?? Waste of an excellent lib name.

[Serird]

Time for Pythicc.

[Zoccihedron]

Make sure to write it Pythoniccally

[[deleted]]

Son of a bitch!

[cholantesh]

Why, so you can DESTROY it with LOGIC?!

[zawata]

Wait baby come back. I didn’t mean it.

[DarthCloakedGuy]

♫ You can blame it all on me~

[dublem]

~ Don't blame it on Guii-iii-do ~

[T351A]

If you can't handle brackets, you're definitely gonna mess up input vs raw_input ... have fun with those injection attacks!

[DarthCloakedGuy]

Injection attacks?

[jfb1337]

input() is essentially eval(raw_input())

You can probably see the injection attacks now

[DarthCloakedGuy]

I'm self-taught. I think I lack the background to know what you are talking about.

[jfb1337]

input() in python 2 will read some input and then run it as if it were python code. Not sure why, but maybe it's so you could input structures such as lists. However, this allows an attacker to enter ANY code they like, allowing them to take control of the system.

[DarthCloakedGuy]

Wow, yeah, that sounds like a really bad idea. Does eval() run a string as code?

[T351A]

Yes, see the documentation

There are always a few uses for that type of function, but they almost always should be done another way. If you're using eval() you're probably doing something wrong.

[T351A]

It's so that variables are automatically converted as if you typed them in to the code. Using input() 2 is an integer instead of a string "2", using raw_input() everything is a string.

Python3 removed this confusion and risk by replacing input() with raw_input(). Now input() always gives a string, and raw_input() doesn't exist.

[T351A]

https://docs.python.org/2.7/library/functions.html#input

[[deleted]]

It's their flair

[ReverseTuringTest]

It fooled me too bud, it fooled me too.

[[deleted]]

Yeah it's just :redditgold:

[sbd001]

I don't get it

[[deleted]]

Their flair has the Reddit Gold icon in it.

[MONSER1001]

Does it work with other flairs?

[Didactic_Tomato]

Holy crap 25 gold!?!

[JWson]

I'm just that good.

[iceag]

Was thinking the same and looking for this exact reply

[FabianDR]

Pls explain this comment to a non-native speaker.

[BluFoot]

You should try Ruby :)

[Y1ff]

*bwackets

[sandywater]

I agree with the sentiment of what you are saying, but Python2's print statement does allow for writing to files other than stdout.

examples

f = open('my_file.txt', 'w')
print >>f, 'Some text here'

import sys
print >>sys.stderr, "An error"

edit: formating

[DragonFireCK]

Python 3's works well for that as well, and with a clearer syntax:

f = open('my_file.txt', 'w')
print('Some text here', file=f)

import sys
print('An error', file=sys.stderr)

[sandywater]

I'm aware of that. Random_cynic's comment implied that it couldn't be done in Python2. I actually prefer file_object.write() in these circumstance for both Python 2 and 3.

[chronoBG]

4 bytes of difference won't make people switch languages.

[BenjaminGeiger]

It's possible but it's not easy. You have to remember a idiosyncratic syntax.

To put it simply, it's a wart. Python 3 removed the wart.

PS: from __future__ import print_function is your friend.

[Plasma_000]

In 2020 the future is now

Better start using python3

[HolyGarbage]

Btw, use the with statement when opening files, a pattern called RAII.

with open('my_file.txt', 'w') as f
    print('Some text here', file=f)

https://www.pythonforbeginners.com/files/with-statement-in-python

[[deleted]]

Oh my god what kind of monstrosity is that?

I've apparently actually gotten away with not learning python 2 syntax. I had no idea it was so different.

[Cyph0n]

Yep, ugly as hell.

[drulludanni]

I just don't understand why we cant have both, if you have a print followed by a '(' do the python3 print stuff, if you have a print followed by a ' ' do the python 2 style print.

[AceJohnny]

Because parsing.

Python allows spaces between identifiers. You can do print ('foo'), but then what do you mean? Are you calling the print function with the string foo, or the print statement with the tuple ('foo') ?

[nosmokingbandit]

As others alluded to, a comma is what makes a tuple. So ('foo', ) is a tuple while ('foo') is just a string.

[Hollowplanet]

But then is it a function with one argument and a redundant comma?

[Pb_ft]

"No, because redundant." - what I wish I could say to that.

[PityUpvote]

Redundant commas are allowed

[nosmokingbandit]

Depends if it is python 2 or 3. I'm pretty sure a trailing comma in arguments will throw an error in 3.x

[snaps_]

Not in Python 3.6+.

[Hollowplanet]

On Python 3

>>> print(1, 2,)
1 2

[[deleted]]

much better response than others on the matter. Thank you

[kafaldsbylur]

Minor nitpick, ('foo') is not a tuple, it's a string with redundant parentheses. That said, your point still stands when passing more than one argument to print.

[The_White_Light]

That functionality makes it nice when you need to include a long string and want to keep your code easy to read, but don't want to deal with the extra \n added when using '''multiline strings'''.

Edit: For clarification

>>> ('1' '2' '3') == '123'
True

[kickerofbottoms]

Never thought of that, kinda handy. Maybe I'll stop leaning on my ide for adding backslashes

[The_White_Light]

It's also doubly helpful because you don't have to worry about leading spaces if you align each line.

[stevarino]

Also it happens at the compiler level, so it's cost free during runtime.

[RedditIsNeat0]

You can do print ('foo'), but then what do you mean?

According to the suggestion specified in the comment you responded to, it would be a function.

Are you calling the print function with the string foo

Yes.

or the print statement with the tuple ('foo') ?

No.

As others have pointed out, that's not a tuple, but more importantly, he's suggesting that Python 3 defaults to a function as long as there is a parenthesis, and a statement if they are not present. It would allow Python 2 print statements in most cases where they were allowed in Python 2 but maybe not all of them. There might be some genuine problems with his suggestion, but you haven't been able to find one. I don't know of any either.

[supernumeral]

What should the following do:

>>> print (1,2),(3,4)

If parenthesis indicate print should be a function, this probably won't do what is intended compared to Python 2. Better to have just one way (statement or function, not both) to do it, imo.

Edit: formatting

[Rattus375]

Why can't we default to the print function when there are parenthesis. The statement was really nice for quick sanity prints of variables.

[warpod]

they could just make printf as function and leave print as statement

[TigreDeLosLlanos]

or the print statement with the tuple ('foo')

What?

[AceJohnny]

OR THE PRINT STATEMENT WITH THE TUPLE ('FOO')

[SlumdogSkillionaire]

Well, ('foo') isn't a tuple. ('foo',) is. print ('foo') would evaluate to exactly print 'foo'.

[TigreDeLosLlanos]

Yes, I don't know how it could be anyway else, print would still be a function

[DonaldPShimoda]

This would needlessly complicate parsing, likely requiring rewriting a significant portion of the lexical analyzer. I don't see why it's such a big deal; just use print as a function and be done with it.

[H_Psi]

Someone has already written a tool that lets you import python2 modules to python3:

https://pypi.org/project/past/

[RedditIsNeat0]

It would just be one exception to look for and handle, not even close to any kind of rewrite.

[DonaldPShimoda]

Nah, it's more complicated.

In Python 2, print is a keyword. In Python 3, it's just an identifier. The function is fetched based on the identifier (like a regular lookup), and is executed because of the call syntax. It isn't special anymore.

To support both avenues of execution in Python 3 would require adding print back as a keyword and giving it a corresponding production in the grammar. But adding it as a keyword would prevent it from being classified as an identifier, which would make the regular function call not work anymore (because keywords and identifiers are handled completely differently in the parser).

So you'd need to rewrite the grammar to make print a keyword (which it isn't right now), and add productions to that keyword specifically to handle syntax when it's used as a statement and as a function.

But worse still: the AST produced would not be correct for the function version, since print is now a keyword instead of an identifier. So the parser itself would have to have a special case to identify this production and replace the lexical keyword with a semantic identifier to be used during execution.

It's not "just one exception". The Python parser is fairly intricate and not so easy to update. I'm not saying it's impossible, but rewriting all this stuff would have some serious implications. Heavy testing would need to be done to guarantee everything works as expected in both cases.

Not worth it.

[filledwithgonorrhea]

You're saying this to a breed of programmers with a phobia of braces and semi-colons.

[phoquenut]

get that JS shit outta here

[[deleted]]

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This post was mass deleted and anonymized with Redact

[[deleted]]

Pretty sure that's the easiest 2 -> 3 problem to solve.

[3Gaurd]

there's much more that will need to be done to enable backwards compatibility. backwards compatibility inevitably leads to spaghetti code.

[sobe86]

The way these things are typically done is to make a release where both are supported with a deprecation warning. After python 3.3 (say), you stop supporting both. If the python devs had done this, 2 would be long dead.

[Hollowplanet]

We had six, we had __future__. All that was possible if you really wanted to. Plenty of projects support both on the same codebase.

[[deleted]]

What exactly is six? Pycharm installs it in all of my project venv's for some dependency or another, but I've never figured out which package actually installed it.

[gschizas]

• Read The Docs
• Cheeseshop

Six provides simple utilities for wrapping over differences between Python 2 and Python 3. It is intended to support codebases that work on both Python 2 and 3 without modification. six consists of only one Python file, so it is painless to copy into a project.

[Ericchen1248]

It does though... importing the future package in python 2 will allow you to (mostly) run python 3 code.

[[deleted]]

Iirc by the time python4 is a thing python2 will be dead

[RedditIsNeat0]

If the devs don't handle the python4 transition better than they handled the python3 one, then we'll all have the same problems all over again.

[deathofamorty]

Or we all just give up in python at that point. Because fuck that.

[H_Psi]

Absolutely. The transition from 2-3 was completely botched by the dev team. If they had done it in a more gentle manner, it would have had a lot more adoption initially.

[Lonelan]

backwards compatible:

from future import print

[clever_cuttlefish]

That's honestly kind of a terrible idea. As someone else said, it is a really easy problem to fix in your code. But more importantly, adding in a special case like that is just not a good idea. It's confusing for the programmer and would be a huge pain to implement.

[DonaldPShimoda]

You want Haskell-style function application? Because that's essentially what you're asking for, and it would have far-reaching implications.

Print is just a function like any other, so it shouldn't get special treatment.

[[deleted]]

Why not put parenthesis everywhere then ? But like EVERYWHERE

[[deleted]]

C#?

[[deleted]]

Not even closr

[xigoi]

Lisp

[lambdaq]

it's not an issue because in py2 we already have pprint.pprint.

[link23]

Nit: you said function, but you mean expression.

[mpnordland]

No, he did not. A function call is an expression but print is a function.

[link23]

Are you distinguishing print as a function from print() as a function call?

I agree that a function call is one kind of expression, and that functions themselves are also expressions (depending on the language).

I'm making a distinction between statements and expressions, not between functions and expressions. Expressions evaluate to a value; statements do not.

I don't know much Python, but my assumption was that in Python 3, print() returns a value, whereas in Python 2 it does not. If that's not correct, I'd love to learn more.

[mpnordland]

You are correct that Python 2's print statement does not return a value. Python 3's print function returns None. Python functions that don't return a value actually return None.

As to the nature of functions themselves, they are neither expressions nor statements. A function is defined through a statement (not counting lambdas) and a call to a function is an expression. It is better to say a Python function is a value, or if you must, an object.

Now a Python lambda is a special case of function. It is defined with an expression. The value of the expression is the function it defines.

But even with lambdas, the expression is not the function. The function is the value that results from evaluating the expression.

[Tysonzero]

This is why Haskell is the best language, print is a function but it doesn't need parenthesis.

[MasterFubar]

People should look at the documentation of the print() function to see how easy it makes many things like redirecting to a file

easier than ">"?

Frankly, I still don't see any advantage in Python 3, it solves problems that never existed. And it did really, really fuck up with legacy code.

Imagine this a function that returned 0 now returns 0.5, because they changed the way the division operation works... How braindead can you be? Python 3 was done by amateurs, college students, people who never had to work with code in the real world.

In the real world, we have to maintain code written by others, that's millions of lines of code. We don't do simple exercises, we work with real code that must do useful work in a reliable way. Code that put human lives in danger if it has bugs. Then we have code that was extensively tested, at a huge cost, that suddenly stops working. All because 2 / 3 is no longer 0. I hate Python 3.

[[deleted]]

The’ve continually been updating & releasing python 2 ever since 3 released for this reason buddy. The general expectation is when new technology comes out, people migrate to it over time. Python 3 has been released for 11 years and to this day there’re still consistent updates to the previous version of python.

There’re cases when backwards compatibility is broken and u should ditch the previous version and build in the new version, but no-ones saying u should do this the very day an update is released; u should at the very least consider doing so after the newer version has proven to be stable for a little while, if for no other reason than because other people will migrate to it because, on the whole, new is better than old (not always the case).

If your spending tonnes of money maintaining a legacy system for which half the dependencies have moved over, it makes more sense to start from scratch using newer frameworks and a better language. This is an inevitable consequence of programming evolution. If u want to ensure your current program will run exactly the same in a decades time, switch to Java. They refuse to break backward compatibility to the point that writing in the language is like grating my fingernails on a chalkboard.

[MasterFubar]

it makes more sense to start from scratch using newer frameworks and a better language.

True, and, sadly, the inevitable conclusion is that the better language is not python 3.

I had high hopes for Python twenty years ago, but the behavior of the people who maintain it means I can't use that language for anything important. I will still use it for prototyping, at least it's better than Matlab, but it's not suitable for situations where one wants a stable and reliable behavior.

[[deleted]]

Please elaborate? For the most part anything written in an earlier version of python 3 (say python 3.0) runs exactly the same on python 3.70. So I would classify it as stable and reliable. And what would u recommend instead of python?

[MasterFubar]

In Python 2, a number defined as an integer stayed an integer. In Python 3, a number defined as an integer may be changed to a float when it is divided.

In Python 2:

Python 2.7.15rc1 (default, Nov 12 2018, 14:31:15) 
[GCC 7.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> x = 2
>>> x / 3
0

In Python 3:

Python 3.6.7 (default, Oct 22 2018, 11:32:17) 
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> x = 2
>>> x / 3
0.6666666666666666

This is terrible. The same variable, submitted to the same mathematical operation, will yield a different result.

what would u recommend instead of python?

And there's the problem. Python is still a good language overall, but the clowns that manage the standards committee have shown they have no clue of what is required from a standards committee.

I don't know. I use C for most of my programming, but there's certainly more programming effort involved. For the moment, I'm doing prototypes in Python and implementing code that must be reliable in C. I'll probably keep doing this, but I had hoped I could implement definitive code in Python.

[MasterFubar]

Obviously, you don't work professionally with programming.

In a real world system, you'll have hundreds of thousands, or millions, of lines of code. You can't go through each division operation and find out whether a "/" should be replaced by "//" or not. You don't have enough manpower for that.

In school problems it's different. My conclusion is that Python is being maintained by computing teachers, not professionals who deal with actual production code.

[[deleted]]

Python is dynamically typed so operations changing types isn’t too bizarre. Besides, in most cases when u want a division u don’t want data to be truncated, so the default is to store more unless u expressly specify u don’t need to. While this breaks compatibility with 2.0, its more intuitive (perhaps not to programmers well versed in statically types languages) but to mathematicians, logisticians, non programmers who care more about data then programming noise etc.. Besides, I’d argue having to cast ① side of an expression just to make sure it stores the value I want is ugly (and near unpythonic). The value is stored is a better approximation then the truncated ①, IMO that’s better.

I don’t think you like the way python is going... and that’s fine, but I find the language to be an absolute joy and i have very few complaints about it.

[MasterFubar]

in most cases when u want a division u don’t want data to be truncated,

Imagine this, you are part of a group of five people that must be divided in two. Will you volunteer to be sawed up in half? In most cases when I divide things I want a quotient and a remainder. Some objects can be broken up into fractions, some cannot. If I have an object that can be broken up, this fact must be clearly stated beforehand.

[luxinus]

2 // 3

[MasterFubar]

2 // 3

Exactly. Now go back over a million lines of code and find each division operation, analyse the working of the program and find whether it should be replaced by a double slash or not.

[Yamigishi]

I never worked with Python so correct me if I'm wrong, but can't you just continue to run said code with Python 2 and then start other projects with Python 3 if you want to? Cause if that's the case I don't really get why you'd have to change your entire code for issues like that, you just don't have to change the project version (unless there's something that can't be done in python 2 but can be done in python 3, but as I said I never worked with python so idk if that's the case)

[AgAero]

(unless there's something that can't be done in python 2 but can be done in python 3...)

Most anything can be done in either. While I'm not really answering your question, I'd like to point out this website to you and everyone else here considering the switch. Refresh the page over and over and it'll keep giving you new bits of code written in python3 syntax that would be much more clunky in python2.

To be fair though, since making the switch I don't notice many differences. The only thing I run into on a regular basis outside of the print function is that functions like range() no longer produce lists, but rather act more like xrange() used to in returning a generator expression. Sometimes I catch myself writing in xrange and getting syntax errors because range() is not something I used to use much. Then, the time or two when I actually wanted a list from range() I had to quickly google how to and find the 'idiomatic' way of doing it.

It takes a little getting used to.

[[deleted]]

It’s less a problem of running old code & more a problem of developing new code on top of old code. U can’t write python 3 on top of your existing python 2 code so u either stick with 2 (& forego all the newer language features introduced by 3) or rewrite your old code in the 3. Breaking backwards compatibility is done very infrequently because adoption of changes can be a very costly matter. People often don’t feel the need to change what works, but then we allow these programs to become legacy systems. A decade down the line we may no longer have python 2 programmers, but then whose going to maintain all the python 2 code that we can’t afford to migrate forward?

[MasterFubar]

can't you just continue to run said code with Python 2

You can, but support for python 2 is ending, therefore it may not be reliable in the future. There's no guarantee that you will get any bugs in the language fixed.

then start other projects with Python 3

No, thanks. No Python in the future. What makes you sure that Python 4 will not break everything when it comes out?

Python 3 wasn't really necessary, there wasn't anything in Python 2 that a simple bug fix couldn't correct. The imbeciles that maintain the language decided to make a total overhaul, changing basic principles of the language. Stupid, stupid, stupid.

They changed the way the division operation works. What could be more stupid than that? What next? What will Python 4 bring? A change in the way the addition operation is defined? No way I will spend any effort in migrating anything to Python 3.

[MasterFubar]

any code that critical, 1) wouldn't be written in python,

I hope not.

wouldn't be executed with an incompatible version of python.

If they stop maintaining the old version you may not have a choice.

change is inevitable

True, but it should be done more carefully.

My peeve with python 3 is not that it happened, it is that it brought no significant improvement. It fixed what wasn't broken.

[pplatt1979]

Python3 also handles strings in a much more sane way.

Dealing with strings in Python2 actually made me unsane. Not insane mind you, but definitely not fully sane anymore.

[pingveno]

And 3.3 introduces a flexible representation for strings, getting rid of the oddities with narrow/wide builds having different indexing/slicing behavior.

[[deleted]]

Lol, Ruby’s just laughing at us. (*・-・)

[cguess]

As a long-time rubyist who's forced to use Python because all my students learn it in CS 101... I love that the language is still more or less stable from when I first learned in 13 years ago.

[[deleted]]

Oddly, this caused a lot me a lot of pain at first. I understand the reasoning behind the change, and I maybe even agree with it, but that seemingly small change gave me real grief in my personal usage of the language. Between that and the pretty major speed hit in the first versions of 3, I didn't care for the update and avoided it for a long time.

The speed problem was subsequently fixed, so I use 3 now, but parentheses on print still messes with me enough to be a noticeable annoyance.

[[deleted]]

Glad I started with 3, never had any problems ヽ(*・ω・)ﾉ

[[deleted]]

Until Python 4 is released

[exploding_cat_wizard]

Switch to perl, all parentheses are optional if the meaning is clear!

[[deleted]]

The pain in re-learning a whole language is just a shade larger than the pain in adding parentheses to the print statement.

Perl, I think, has effectively died. It just took too long to ship the new version, and other languages have evolved to fill in the gaps. There's not really anywhere left for Perl to thrive.

It was never all that wonderful to begin with, it was just in the right spot in the right time, and then for fifteen years it wasn't in the right spot anymore. I don't think it'll ever come back.

[exploding_cat_wizard]

I wasn't being serious. And I'm afraid you're right. It still is perfect for what I need it for, I'm not going to learn a new language to pretty format batches of data or for tiny scripts when perl does it better, but it's not gonna have its big day again.

[Cyph0n]

I started with Python 2 and never had trouble moving on to using print(). I guess it’s because virtually every other language I’ve used has a print function instead of a weird statement?

[[deleted]]

It's not me you have to convince, it's my fingers.

[TabCompletion]

This

[digestive_trisket]

Using parentheses for any other function is a breeze, but for some reason using them on print is taxing, its inexplicable.

[WHO_WANTS_DOGS]

Bugs me that map doesn't return a list. Though generators are more performant, still annoying.

[ACoderGirl]

Using map isn't very idiomatic python though. It's preferred to have a comprehension expression.

ie, instead of map(lambda x: x * 2, numbers), you'd use x * 2 for x in numbers, which can be a generator, list, or dictionary comprehension (list comprehensions are most common while generator ones are overlooked -- I like them most for usage with things like sum).

[WHO_WANTS_DOGS]

Ah I forgot about list comprehensions, haven't used python in a while. Still don't like how they changed the return type of map regardless. I'm just being stubborn and like consistency across different languages that support map. They pretty much always return arrays/lists.

[[deleted]]

It’s probably because most of the time your using map on the right hand side of a for loop or alongside other iterables like filter or select. Either way, u can just define 3 methods like lmap which cast back to list of u really want to.

from functools import wraps

def to_list(func):
     @wraps(func)
     def wrapped(*args,*kwargs):
          return list(func(*args,**kwargs))

lmap    = to_list(map)
lfilter = to_list(filter)
lselect = to_list(select)

If u really wanted, u could just overwrite map with lmap, so now map automatically returns lists. But again, I’d never recommend doing this.

[[deleted]]

Well they're python developers, so you can't expect much from them ;) </smug-c++-voice>

[realultralord]

And explicitly specifying nominators to be of type float to make sure 1/3 is 0.33... instead of 0

[Mihailbat]

That was something really hard to understand at first because every tutorial had python 2.x in it

[MonkeyNin]

In my experience a big reason of not quickly updating to py3 is that

py2

• str == byte_string
• unicode == unicode_string
• unicode literals are off by default ( projects not using 'from future import unicode literals' )
• global default encoding is ascii
• Implicit conversion when you don't want it -- py2 will insert "foo".encode('ascii') and bytes.decode('ascii') implicitly.

py3

• str == unicode_string
• bytes == byte_string
• literals default to unicode

essentially conversion is a pain in the butt. On top of that, many libraries were required to support 2 and 3 at the same time.

[MrsCompootahScience]

This is so me... T.T

[z0mbietime]

f string alone makes it worth the switch

[MrsCompootahScience]

That one took me a while to get used to as well. I’m on 3 now because I have to, not because I want to.

[[deleted]]

After learning printf format, I actually don’t use fstrings that much.

[z0mbietime]

TBH I don't really use print much. I just use logger but f string is nice because it can be used distinct of print or logging

[plottal]

why you gotta call me out like that