What’s New in Python 3.8 • Hacker News Board

Re: What’s New in Python 3.8

#171

Post by hermitdev » Tue, Oct 15, 2019, 4:58 AM UTC

murkt wrote: post #156

hermitdev wrote: post #124

Earlier quoted context omitted.

Yes, but your example is less efficient than the new code. Remember: every variable is an assignment into a dict, and every lookup a query into a dict. Reducing name lookups and assignments can yield good speedup in tight loops. For instance, caching os.path.join, os.path.split into local names can significantly speed up tight loops iterating over a filesystem. For example, os.path.split is potentially 5 dictionary l…

Local variables aren’t stored in a dict, likewise when a class has defined __slots__. Globals, modules and usual classes do use dicts internally, but locals do not. So from the efficiency standpoint it’s (almost?) the same. I haven’t checked the bytecode, maybe there is some slight difference.

It has been a while since I've looked at the implementation details. How does locals() work, then? It does return a dict. Slots are definitely an edge case I did not address. I honestly dont know how name lookup works in any version of Python.

Edit: I realize that local name lookup doesn't need to follow the result of the locals() built-in function.

Re: What’s New in Python 3.8

#172

Post by manojlds » Tue, Oct 15, 2019, 5:11 AM UTC

paulddraper wrote: post #73

CivBase wrote: post #22

As a developer who has primarily developed applications in Python for his entire professional career, I can't say I'm especially excited about any of the "headlining" features of 3.8. The "walrus operator" will occasionally be useful, but I doubt I will find many effective uses for it. Same with the forced positional/keyword arguments and the "self-documenting" f-string expressions. Even when they have a use, it's us…

> As a developer who has primarily developed applications in Python for his entire professional career, I can't say I'm especially excited about any of the "headlining" features of 3.8. Python is a fairly old, mature language. What features would you have been especially excited about?

Yeah the fact that a new release is boring is a good thing.

Re: What’s New in Python 3.8

#173

Post by penagwin » Tue, Oct 15, 2019, 5:12 AM UTC

shaklee3 wrote: post #167

levi_n wrote: post #127

Earlier quoted context omitted.

Though not a language feature per say, I would love if the language would take on the packaging ecosystem and deliver a ground up approach that isn't just a kludge on a kludge on a kludge.

I've heard people recommend poetry on here as something that is good for package management, but I haven't tried it. Does anyone know of something like that, but also can build your application into a Docker container as well?

Into a docker container as well? The package manager isn't really related to docker though?

Does your container expose ports or need volumes? Does it need gunicorn or uwsgi in front of it? What about system packages? None of those (except maybe the last one) are really in the scope of the package manager.

Re: What’s New in Python 3.8

#174

Post by jakear » Tue, Oct 15, 2019, 5:24 AM UTC

murkt wrote: post #156

hermitdev wrote: post #124

Earlier quoted context omitted.

Yes, but your example is less efficient than the new code. Remember: every variable is an assignment into a dict, and every lookup a query into a dict. Reducing name lookups and assignments can yield good speedup in tight loops. For instance, caching os.path.join, os.path.split into local names can significantly speed up tight loops iterating over a filesystem. For example, os.path.split is potentially 5 dictionary l…

Local variables aren’t stored in a dict, likewise when a class has defined __slots__. Globals, modules and usual classes do use dicts internally, but locals do not. So from the efficiency standpoint it’s (almost?) the same. I haven’t checked the bytecode, maybe there is some slight difference.

I checked the bytecode, in the walrus version you get [...DUP_TOP, STORE_FAST, ...] in the non-walrus you get [...STORE_FAST, LOAD_FAST, ...]. Besides that identical. I imagine DUP_TOP is faster than LOAD_FAST, but I feel either way this is useless micro optimization at its finest.

Re: What’s New in Python 3.8

#175

Post by jakear » Tue, Oct 15, 2019, 5:29 AM UTC

pcr910303 wrote: post #48

I like the additions of the f-strings and walrus operator, but I find myself wishing a breaking-release removing the old features that the new features covers. Python's philosophy was to have one way to do something, but the current situation of Python is very inconsistent. Python 3 has like 4~5 ways to format strings, and due to the addition of the walrus operator, we have (I understand the differences between := an…

That's a good use case for a linter. Ban outdated constructs in your code, but still allow you to depend on things that use them. Beats another 2->3 split again.

Re: What’s New in Python 3.8

#176

Post by MichaelMoser123 » Tue, Oct 15, 2019, 5:33 AM UTC

gizmo385 wrote: post #46

kolinko wrote: post #39

Earlier quoted context omitted.

I actually found an immense use for Walrus - used it to hack Python into doing pattern matching that is way more readable than without it: https://github.com/eveem-org/panoramix (source code for Eveem.org, which is arguably the best decompiler for Ethereum smart contracts out there. you can see a lot of pattern matching in pano/simplify.py , and I found no way to do it without extending the language/walrus while main…

After a quick read through, I personally find this syntax much harder to read using operator overloads than it would have been using a series of comparison functions. Tilde is a very obtuse operator and I don't know that this really buys you anything. Feels like a case of preferring cleverness over readability/usability/maintainability.

Python is adding features, maybe they want to be as expressive as perl, when they grow up; however that comes with the price of decreased readability.

Re: What’s New in Python 3.8

#177

Post by pcr910303 » Tue, Oct 15, 2019, 5:33 AM UTC

jakear wrote: post #175

pcr910303 wrote: post #48

I like the additions of the f-strings and walrus operator, but I find myself wishing a breaking-release removing the old features that the new features covers. Python's philosophy was to have one way to do something, but the current situation of Python is very inconsistent. Python 3 has like 4~5 ways to format strings, and due to the addition of the walrus operator, we have (I understand the differences between := an…

That's a good use case for a linter. Ban outdated constructs in your code, but still allow you to depend on things that use them. Beats another 2->3 split again.

Yeah, and I already use linters to remove all outdated constructs; but... It's a pity that "There's only one way to do it" doesn't work in 2019 :-(

Re: What’s New in Python 3.8

#178

Post by cryptos » Tue, Oct 15, 2019, 5:34 AM UTC

It would be nice if the Python web site would be mobile friendly.

Re: What’s New in Python 3.8

#179

Post by raobit » Tue, Oct 15, 2019, 5:40 AM UTC

hermitdev wrote: post #119

CameronNemo wrote: post #67

Earlier quoted context omitted.

Easy. Don't buy products that are obviously still using python2. Problem should solve itself in some time. Hard to tell sometimes, but looking at dependencies and plugin languages is a good way.

The only software I've written in Python that's been sold was written against 2.5 and has long been out of my control. We sold the source to the sole client (was a financial services migration tool for a very specific domain during a joint venture; I can't divulge anymore). I know longer work at the company, but i'd wager that the client wouldnt have been willing to pay $500/hr (the rate my company billed me out at f…

what is your take w.r.t to other backend languages if you have worked with any?

Re: What’s New in Python 3.8

#180

Post by jakear » Tue, Oct 15, 2019, 5:41 AM UTC

jakear wrote: post #174

murkt wrote: post #156

Earlier quoted context omitted.

Local variables aren’t stored in a dict, likewise when a class has defined __slots__. Globals, modules and usual classes do use dicts internally, but locals do not. So from the efficiency standpoint it’s (almost?) the same. I haven’t checked the bytecode, maybe there is some slight difference.

I checked the bytecode, in the walrus version you get [...DUP_TOP, STORE_FAST, ...] in the non-walrus you get [...STORE_FAST, LOAD_FAST, ...]. Besides that identical. I imagine DUP_TOP is faster than LOAD_FAST, but I feel either way this is useless micro optimization at its finest.

In cpython:

DUP_TOP:

            PyObject *top = TOP();
            Py_INCREF(top);
            PUSH(top);
            FAST_DISPATCH();

TOP:

            (stack_pointer[-1])

LOAD_FAST:

            PyObject *value = GETLOCAL(oparg);
            if (value == NULL) { /* throw */ }
            Py_INCREF(value);
            PUSH(value);
            FAST_DISPATCH();

GETLOCAL:

            (fastlocals[i])

So looks like either way, you have an array access of something definitely in cache, a Py_INCREF, a PUSH, and a FAST_DISPATCH. The walrus operator saves you a null-check, but that check is probably skipped right over by the branch predictor, as it always throws. I'd bet the performance is indistinguishable, but I'd be interested to see for real.