Python tricks: Type hints and static type checking

[@zakariaabderrahmanesadelao3048]

that is the clearest and simplest explanation for type hints. thank you man.

[@austinhaider105]

I've learned everything I know about Python from KZbin and your videos are some of the best I've come across. I appreciate the amount of detail you go into about every topic; keep it up!

Thank you!

[@francescofaccia]

Good job Seb. Very well explained. Clear and synthetic!

[@arachnid83]

Thanks for explaining this. Your explanation was very deep and clear. I was a little perplexed with this concept.

[@david-oj2je]

Thanks I absolutely love your videos

[@raspreetsingh5542]

An amazing explanation dude, I was having some difficulty understanding the callable type hints but you did such an amazing job of ELI5ing it. Thanks a lot :) and keep the great content coming

[@nelsonmacy1010]

Very clear and to the point. Appreciate

[@xmandeng]

Really helpful overview. Thanks!

[@pyadaaah9866]

Nice video - thank you! Maybe you also could be interested in Pyadaaah, which provides runtime (!) type AND range checking?

[@barulli87]

everything is clearly explained! cheers!

[@mivoe99]

This is a great video on the topic

[@debSha007]

Hi, For the first program I'm getting "Incompatible return value type (got "None", expected "int")" how to deal with it ?

[@javierbosch1338]

I'd love to get a list of your atom Python Packages that you are using. the REPL, autocomplete , etc. packages

If memory serves me, I was using magicpython, for correct syntax highlighting, and autocomplete-python for (obviously) autocompletion. The terminal that you see on the left isn't part of Atom though-it's a standalone Linux terminal!

[@wolverinerazor]

which Linux distro do you use? btw, amazing videos. when will you become a trainer on pluralsight/ lynda etc?

[@flyingsquirrel3271]

Is None still always accepted by mypy? And if yes, why are they not using the "Optional" class from the typing module for that?

It seems they've changed this behavior (as default) as of MyPy 0.600, released last May. Now, None is no longer compatible with any type, but rather (as you say) you need explicitly allow None using the Optional type hint. An improvement in my opinion!

[@thecodebear]

I really enjoyed it. Very usefull video . Thank you so much for this

[@compucademy]

Nice. Clear and helpful.

[@wentaoqiu4072]

Your explanation is amazing, and your outfit is stunning..

[@justchary]

Man, you good! Thanks for explanation.

[@rafadydkiemmacha7543]

PHP has real type hints. I was surprised to find out that Python’s interpreter ignores them.

[@springinfialta106]

Static Typing rules!

[@rafadydkiemmacha7543]

It does, but Python doesn't handle that too well.

[@sudharsan4040]

Thanks for the informative video.

[@RodrigoStuchi]

👏 👏 👏 👏, very nice explanations, thank you!!

[@jeremyclark9697]

Thank you!

[@reydavid7300]

Which code editor is that?

[@RajveerSingh-yb6zq]

Except, Negative number have factorials :) And float have too... :)

[@soldadopreciso]

interesting video, thanks pal, go ahead.

[@lazypunk794]

Anyone else getting an error in factorial function while doing mypy type checking. It says return type got "None" expected "int", which actually makes sense because we are returning NOne for a certain case when we have mentioned that return type is int. Why is that error not popping up for you? Seems mypy got some smarter updates since

[@lazypunk794]

And now passing "None" where "int" is expected gives error in mypy.

That's right. I believe that previous versions of MyPy (as I'm using in the video) always accepted None, whereas modern versions more sensibly don't. After all, int != None

[@lazypunk794]

@ this actually causes another issue. Now in your type hints, you cant use "int" as your return type for the factorial function since we return "None" when number = 0. you are forced to use "Any" as return type.

[@Serotonindude]

optional static typing... :D am i wrong, or is it like: 1) if static typing would have saved you... of course, you didn't use it 2) if i take my time to give proper type hints... why does the runtime not care at all? i may optionally type check it with another program... i don't know... feels like do it right all the time or just leave it

I agree that the current implementation of static typing is a bit half-baked. But I wouldn't be surprised if future versions of Python will allow you to enforce the type hints, and that could be very useful in some cases. (I have no inside information to support this, but just based on common sense I suspect that the Python devs will move in that direction.)

[@ambig1]

what webcam do u use? it is so good....

+Gajendra Ambi I'm using a Canon 750D, which is a decent photo camera.

[@AliHasan-xh8in]

Thx for the tutorial

[@oleholgerson3416]

what about classes? how can you check for those?

That's actually really straightforward, because you can directly specify the name of any class in a type hint, as you can see below. It only becomes more complex if you want to specify details about the class, such as in the case of List[int], which specifies not only that you expect a list, but also that it should be a list of ints. class MyClass: pass def print_myclass(v: MyClass): print(type(v)) myobject = MyClass() print_myclass(myobject)

[@ukaszx4072]

Hi, Can someone explain me why there is a this -1 in line "return i*factorial(i-1)". I tried without that -1 run my code and it fails, but why? And which part of this code knows to divide some value like 3 into 1x2x3?

This is a classic computer-science exercise. You can find more details about it here: python.cogsci.nl/basic/functions/#exercises

[@johnmarquess7375]

Useful. Thanks.

[@deadc0de517]

Isn't it proper to use Dict[Hashable,int] instead of Any as key?

That's an interesting question. Strictly, there's no difference, because the keys in a dict are by definition hashable. However, you could say that making this property of dicts explicit in a type hint makes code more readable. On the other hand, most people probably don't know what hashable means, so I would be inclined to say that it makes code less readable.

[@ArjunPatel-gk9lq]

what compiler is this?

Since Python is an interpreted language, there's no compiler involved! (That term is generally reserved for programs that translated compiled languages like C to machine code.) But the editor that I'm using is Atom. And the static type checker is MyPy.

[@ArjunPatel-gk9lq]

@ thank you! i have a lot to learn about python lol

[@vineethgeorge7387]

bro i need this intro song loved it verymuch

[@rafadydkiemmacha7543]

Coming from PHP, type hints in Python are actually really disappointing. The fact that they require external arbitrary tool to do anything is just weird. But the fact that None always passes makes type hints in Python virtually useless in my book.

[@asdf3568]

But it still returns None and doesn't complain

[@valizeth4073]

Dynamic typing is aids.