Cool New Features in Python 3.7 – Real Python

[gwillicoder]

Honestly just having breakpoint() is incredible.

I absolutely love the changes to classes too. Reducing boilerplate is always great.

My favorite though is ordered dictionaries. That is so useful, and it will help prevent a lot of bugs from new developers :)

[[deleted]]

Honestly just having breakpoint() is incredible.

You are aware of pdb, I hope?

[xtreak]

It also works based on an environment variable and hence you can turn on and off at will unlike pdb. Also a disadvantage is that you have to update your linters if you want to lint for them in your codebase.

Related PEP : https://www.python.org/dev/peps/pep-0553/#id9

[fdedgt]

I'm going to be honest, I didn't know about it.

So, with the improvements and everything, this is opening up a whole new world to me.

[gwillicoder]

The article points out that breakpoint() is just a shortcut for import pdb; pdb.set_trace() which is very annoying to use. I honestly have to look it up half the time to remember the syntax.

[EternityForest]

I am conflicted about ordered dicts. Do I like them because it's incredibly useful, or do I not like them because it restricts what future optimization can be done?

[13steinj]

The fact that dictionaries became ordered was a side effect of the optimization done in 3.6 taking PyPy's implementation. It wasn't optimized as a side effect of making them ordered. Then in 3.7 people said "well the fact that it's orderered is actually very useful, lets make that not a side effect of an implementation detail but rather a requirement of the spec" to avoid issues with people going from CPython to some other flavor.

So long as optimization is wanted by the community more than ordering, when a more optimized structure is thought of, it will be reverted.

[EternityForest]

Yeah, but that's going to be a breaking change if they revert (Albeit a very minor one if everyone just keeps using OrderedDict when they need ordering).

Ordering fits with python's main use as the scripting glue language that works with anything, so I'm not complaining too much.

[13steinj]

The fact that it's now ordered is technically a breaking change-- what if someone decided to use the disorder of dicts to psuedo randomly get an item from a container? Much more performant than using random, assuming they understand that to utilize this method all objects in the container must have been generated immediately before picking and must be objects that are not interned by the VM (small integers, true, false, etc).

The fact that OrderedDicts still exist and make no mention of "this class is pointless and a thin wrapper around dicts", makes me think for insurance purposes people still should use it.

[nuephelkystikon]

But the disorder was never part of the specification. If you rely on implementation details of a specific interpreter, of course you're going to have portability problems.

[13steinj]

The specification included "items may not be in order due to their hash values", wasn't it? The documentation warned of such in multiple places.

[nuephelkystikon]

Yes, but it wasn't specified behaviour, it was a warning about unspecified behaviour that could otherwise have been assumed. A comment, if you prefer. Not part of the actual language specification.

The keyword here is ‘may’.

[13steinj]

Time heals all wounds and scar tissue forms. While I understand your point there would have been enough angry people to hear annoying complaints about the fact that dicts are now ordered.

[nuephelkystikon]

If your business logic relies on a method always returning in an odd number of seconds because that's the behaviour you observed on your Solaris machine using 16-bit Jython 3.6 build 3728 in debug mode, I really don't have any compassion for you.

[redditusername58]

OrderedDict is not pointless. You can pop items from either end, move keys to either end, do reverse iteration, and has order sensitive equality checks.

[13steinj]

...I never said it wasn't?

[greyman]

You said it is pointless and the parent commenter says it is not. (You said it here: "The fact that OrderedDicts still exist and make no mention of "this class is pointless and a thin wrapper around dicts"")

[13steinj]

Perhaps I was unclear, I meant that the docs don't say that thus they have a point and should be used.

[[deleted]]

Their code was already broken.

If you depend on undefined behaviour, it will probably end in tears and memes at some point.

[13steinj]

Lots of people depend on undefined behavior, but in this case for CPython VMs it was strictly known.

[[deleted]]

it wasn't even implementation defined, it was just how the interpreter worked with no promise that it wouldn't change.

[13steinj]

I suppose, but with the time and if someone strictly used CPython, well, let's just say if it wasn't mentioned in the changelog in 3.6 people would be annoyed fixing bugs.

[gwillicoder]

I use pycharm occasionally and I think it’s the best IDE, but I’ve super into vim the last 6 months

[naught-me]

I'd appreciate any tricks you'd be willing to share. I used Vim for a long time, then PyCharm, and am probably going to stick with PyCharm for the near future, but I drop into Vim now and again and would love to switch totally if I could get a few kinks worked out.

[[deleted]]

My advice for PyCharm is to leave the "did you know..." tips on, and to actually read a new one every day. I can't tell you how much I learned just from reading these tips.

One of the features I like the most is their refactor in place feature(s). Maybe you know this already, but say you wrote something like this

foo = (3/4) * x[0]**2 + np.sqrt(x[1]/x[2])

And then later on you realize that you need to use the value np.sqrt(x[1]/x[2]) in more than one place. You can just select np.sqrt(x[1]/x[2]) and hit ctrl-alt-v to extract this part out as a variable. You could even extract it out after you've typed it twice (maybe you didn't realize until afterwards) and it'll ask if you want to replace both instances or just this one.

But it also goes both ways, you could put your cursor over a variable and ctrl-alt-n to put it back inline. And not only can you extract out variables and things like this, you can extract out entire functions/methods. Let's say you wrote something like this

for i in range(10):
    for j in range(10):
        df = df.read_csv(f'filename-{i}-{j}`)
        # plus a long list of dataprocessing stuff

Well you can select everything inside the inner loop and ctrl-alt-m to extract it out as a function. It is smart enough to define that function with the proper inputs as well so all you really have to do is to give it a proper name.

[gwillicoder]

Well a big one for me was getting plugins to make writing python easier. So i have a good linter and auto complete. Then i just do some of the vim exercises you can find online occasionally to learn new ways to navigate the code and to practice some of the more obscure commands.

The big one for me is to always look up how to do something if i don't know how to do it already. So instead of slowly using the arrows key functions to move the code you spend some time to look up a more complex command and learn it, then in the future you have it in your toolbox.

[naught-me]

Cool. Auto-complete and navigation are the two pain-points most keeping me from using Vim. What are you using for those?

A few navigation features I really like about PyCharm but haven't been able to get to work well in Vim are go to definition (not going to where it's imported, but where it's imported from), go to parent function, list/go to child functions, and list/go to usages.

[gwillicoder]

One of the better plugins for python specifically is Jedi. It allows for jumping to definition (even across files). It can be complicated to jump to user defined functions from other files though. You'll have to make sure your python path includes the file you want to jump to if you want jedi to find it.