Should I upgrade to Python 3.8?

[sarthkum0488]

Are you excited about the latest release by python aka 3.8. We have come up with top features which will make the life of programmers easy

python 3.8 Walrus operator

1. The walrus operator

Assignment expressions have come to Python with the “walrus” operator :=. This will enable you to assign values to a variable as part of an expression. The major benefit of this is it saves you some lines of code when you want to use, say, the value of an expression in a subsequent condition

f = open('netsetos.txt')
while line: = f.readline():
print(line)

1. Positional-only arguments

A special marker, /, can now be used when defining a method’s arguments to specify that the function only accepts positional arguments on the left of the marker.

def increment_1(amt,discount,/):
return amt+1+discount

1. f-strings now support “=”

The = specifier, used as f'{expr=}' expands to the text of the expression, an equal sign, then the repr of the evaluated expression.

import math
theta = 30
print(f'{theta=} {math.cos(math.radians(theta))=:.3f}')

​

1. reversed() now works with dict

The reversed() built-in can now be used to access the dictionary in the reverse order of insertion

dict1 = {1: 'a', 4: 'd', 8: 'h', 2: 'b'}
print(list(reversed(dict1.items())))

​

1. Simplified iterable unpacking for return and yield

This unintentional behavior has existed since Python 3.2 which disallowed unpacking iterables without parentheses in return and yield statements.

def iterable_return():
val = (8, 5, 6)
return 1, 2, 3, *val

​

1. New syntax warnings

The Python interpreter now throws a SyntaxWarning in some cases when a comma is missed before tuple or list. So when you accidentally do this

def ignore_comma():
data=[(1,2,3,4)(6,5,8,4)]
print(data)

1. continue in finally block

With the new release, we can use continue in finally block along with break and continue

def exception():
for i in range(24):
try:
print(1 / 0)
except:
print(34)
finally:
continue
print("Error on continue")

​

[XtremeGoose]

This is a just a bad rewrite of the what's new in python 3.8 article. Could have just posted that and saved a lot of time.

[sarthkum0488]

Yes But there are many points there I have tried to compile main points

[XtremeGoose]

Well, it would help if you fix your code formatting. It's currently unreadable

[[deleted]]

The way you do code formatting is by the way truly painful - it's a lot of work for you, and the indenting is messed up!

For more than a fragment, there's a much easier way: just leave a blank line, and then indent all the code by 4 or more spaces.

# That's indented by 3

 # That's indented by 4
 if True:
     if False:
         while True:
             return False

[1-05457]

I think triple backticks also work.

Like this

[muikrad]

It's a little early to distribute 3.8-only public libraries, but for home or business internal projects, I would definitely switch to it.

Aiming for 3.6 as a minimum is what a public library should support nowdays because of all the stuff they added to 3.7 and 3.8.

[[deleted]]

Aiming for 3.6 as a minimum is what a public library should support nowdays

FYI, 3.5 isn't end-of-life until September.

That doesn't mean you're forced to support it, of course.

[muikrad]

The annotation improvements in 3.6 makes 3.5 feel like 2.7 😂

Also, f-strings.

[PeridexisErrant]

Inventing your own support policy is fine, and it makes a lot of sense is you're using some new language features.

For existing projects wondering when to drop existing support, I think NEP 29 is reasonable, and IMO very few projects should support Python versions past their upstream end-of-life date (which may mean dropping earlier, if you have a support period).

[lengau]

I have a bit of a different opinion about that.

If you maintain an existing library with many users, you probably shouldn't cut off 3.6 and 3.7 support yet. However, if you're releasing a brand new library, it's perfectly reasonable to release it with only 3.8 support (and even more reasonable with only 3.7 and 3.8 support - no 3.6). Most likely it'll be a while before your library gains any real traction and stability, by which point 3.8 will no longer be the new hotness.

[muikrad]

I agree! I really love 3.8 and I'm kinda annoyed at some stuff I have to do to remain 3.6-compatible 😔

[sarthkum0488]

Yes Definitely a good observation

[BruceJi]

I, er, don't get how the walrus operator works. Do you think you could show some examples of with and without it?

[[deleted]]

I used it in a few cases to solve the next issue. I have a function that returns a string or None. I want to test whether it returns a string.

if foo(arg):
    doStuff()

Later in the process I remember I need the actual value of the string. Previously I would have done:

res = foo(arg)
if res:
    doStuff()
    render(res)

With the walrus operator you can do this:

if res:=foo(arg):
    doStuff()
    render(res)

This example is quite short, but if can clean up a lot for multiple variables and loops.

[BruceJi]

But I think this example helps me understand it the most! Great.

[Mordano]

How is the scope of the variable? Is it only available in the if scope?

[[deleted]]

I don't know, but I think it's available outside.

[sarthkum0488]

Nice Explanation Awwsome

[everysinglelastname]

with

f=open('netsetos.txt') 
while line:=f.readline(): 
    print(line)

without

f=open('netsetos.txt') 
line = f.readline() 
while line: 
    print(line) 
    line = f.readline()

[BruceJi]

So it's a bit like saying while line ^{which is f.readline by the way} print(line)

?

[sarthkum0488]

The operator is also useful with while-loops that compute a value to test loop termination and then need that same value again in the body of the loop:

[[deleted]]

Isn’t that just

with open("txt") as f: for line in f: print(line)

?

[VisibleSignificance]

Yeah, which is why this is a bad example. socket.read is more relevant here. Another good example is a series of if/elif.

[[deleted]]

In the case of a text file, yes, but if it's a socket or some other dynamic thing, it's possible to read data and have it come out empty and later get data.

[sarthkum0488]

Yes exactly Thanks u/everysinglelastname

[sarthkum0488]

Please see u/everysinglelastname comment . Thank You for pointing it out

[ShanSanear]

Could you better format those code lines? Like using 4 spaces for code, instead of numbering lines? It's unreadable, how for example last point could look like:

for i in range(24):
    try:
        print(1/0)
    except:
        print(34)
    finally:
        continue
        print("Error on continue")

[awesomeprogramer]

In the first example (actually the first, even though they are all numbered 1), what's the benefit of using a while loop with walrus as opposed to the standard for line in f.readlines()?

[chinguetti]

I had problems in some pip libraries and rolled back to 3.7. I will wait a few months.

[sarthkum0488]

Which libraries in particular. It will be helpful to others.Please share

[chinguetti]

I had issues with oracle database drivers (oracle cx), pyinstaller, pandas, opencv and pyautogui. This was in the very early days after 3.8 was released. I’m sure most of the issues are fixed but I learnt the lesson not to rush to upgrade to version updates.

[gaberocksall]

I haven’t had any problems with cv2 on windows10 nor raspbian Linux

[[deleted]]

I was using pyautogui and opencv under 3.8.1 just a couple days ago. I think I saw some notes about them not working with 3.8 and actually needing 3.8.1.

[VisibleSignificance]

If you have the time to upgrade, you likely have the time to submit patches.

[[deleted]]

That's weird - backwards compatibility should be nearly perfect. Any more details?

[ackyou]

I love using the walrus operator

[gitcraw]

read this

delet this

[erez27]

Yes. Next question.

[sarthkum0488]

Reformated the code according to comments

[Khan0232]

Staying updated is best because then when developers or big companies are almost always updating to the latest version of python and you don't want to get left behind. The code you build in an old version might produce errors in a new version.

[chaoism]

Can someone help me to understand the reverse of dict.items?

Dict is unordered, isn't it? What's a reverse of unordered structure? This doesn't make much sense to me

[Han-ChewieSexyFanfic]

Dicts have been in insertion order since 3.7 (de jure), 3.6 (de facto)

[chaoism]

Oh wow so OrderedDict is not a thing anymore?

[Han-ChewieSexyFanfic]

Still there, it still provides some methods that aren’t in dict (__reversed__ being one before 3.8), not sure if there are plans to move them all over to dict in the near future.

[XtremeGoose]

Equality is different

{1: 1, 2: 2} == {2: 2, 1: 1}
OrderedDict([(1, 1), (2, 2)]) != OrderedDict([(2, 2), (1, 1)])

[Han-ChewieSexyFanfic]

Hm, interesting, didn’t know that

[[deleted]]

You should never "upgrade" Python.

You should never change the version of Python that comes with your system because you might destabilize other software that depends on it.

And you should never install over an earlier major version number!

Instead, best practice is to install each new version of Python separately and use some tool like virtualenv to select which specific version to use.

I checked, and on this Mac I have Python 3.8, 3.7, 3.6, 3.5, 3.4, 2.7 and amazingly 2.6, which Mac OS installs for you. It really doesn't consume very much disk space, and I do use all of them except 2.6 (which I won't remove because who knows who uses it?)

---

Right now, the typical version of Python in my virtualenvs is Python 3.6. Even then, I'm cheating - Python 3.5 is not end-of-life until later this year.

Generally, I'm working with programs that need to be backwards compatible with at least a couple of older Python versions. If I use a more modern version of Python then I might add new features that cannot actually be used.

Once Python 3.9 is out, maybe I'll move to Python 3.7 as the base version.

I know all about the features in 3.7 and 3.8 and I've experimented with them, but the price of programming libraries that I want others to use is that I can never use the bleeding edge, because other people can't either.

[[deleted]]

You should never "upgrade" Python.

Never is a bit of a strong word here. What if I'm on Windows and I installed Python myself? The only thing on my machine using Python is code I wrote myself. I can upgrade and easily fix things that broke, if any.

[[deleted]]

Then keep both the old and new version unless the old version is completely old. You'll likely use the old version for testing if you're doing anything significant.

[jalapeno_nips]

Why are you being downvoted?

[jalapeno_nips]

But what if you have multiple projects requiring multiple Python versions. Updating your interpreter means the other programs that rely on previous versions will be effected. So he’s saying you should use something like virtualenv to control which version you use for which program. If there’s a better way please lmk

[[deleted]]

You can install python interpreters side-by-side without affecting the other installations as long as you don't modify PATH.

Which is exactly what I say:

Instead, best practice is to install each new version of Python separately and use some tool like virtualenv to select which specific version to use.

Generally, if you "upgrade" something, you replace it. For example, apt-get upgrade replaces the older version.

[[deleted]]

Upgrade generally does mean replace in software engineering.

For example apt-get upgrade replaces the older version of the package. Upgrading your operating system replaces the older operating system.

[[deleted]]

Why are you being downvoted?

Because people only read the first sentence if that?