My personal experience with compile time type checking is that the benefits kick in for a single developer project within a week, and for a multi-developer project immediately.
Python can be as strongly typed as you like it to be. But of course, with Python, instead of insisting on an incoming parameter being of a particular type, the thing to do is Pythonically ask nicely if it can be the type that you want. If you need parameter x to be a float, call float(x), which will raise TypeError or give you a float. And of course, it gives the implementor of the class the option to implement __float__().
With a small amount of effort, you can design all of your __init__() constructors to do that style of validation. Yes, it requires some elbow grease. But you will not be able to pass bad stuff to my __init__ constructors if I don't want you to. And if you want some parameter y to be an instance of Foo, just call Foo(y) and if it is already a Foo, you get the Foo, and if it can be made a Foo, you get a Foo, and if it can't, you get TypeError.
So of course you actually need to exercise the code also, which is where the hypothesis package comes in.
Anyway, I think one of the reasons Python is popular is that it is very consistent about types. Haskel and Rust are also very consistent about types -- most other languages, not so much. Give me one end of the spectrum or the other. The murky middle is suboptimal.
It requires among other things, a unique and toilsome coding style, constructor overloading (which isn't a first class citizen of python), and you only get late runtime validation (which means, for example, you can easily miss type validation on only one side of a conditional).
Something like pytype detects such errors without any code modifications.
But certainly, it doesn’t remove the need for good test coverage. Now, if you want to argue for less testing, that is a different pitch.
Factory methods are usually better, and I believe what the more modern parts of the standard library have tried to use, but they don't work as well for this specific case.
Once you start doing this in python -- beyond any low complexity usage -- you're better off capturing your arguments in their own object and passing this to the function as a single argument. This object can then enforce whatever you want, and your function can now be a class method.
And then you can build a factory for this object that accepts a few args, maybe some keyword parameters. But, once that gets reasonably complex, just rinse and repeat. It's objects, methods and factories all the way down. And unlimited billable hours.
But once you have type validation i don't really see the use case anymore. Common example of how silly this is is functions that have a special case for handling lists of length 1 by allowing the object to be passed in without being part of a list, eg Union[List[Foo], Foo]. Now you need extra code to handle that special case in your function and the type annotation becomes more verbose. Much easier to just enforce List[Foo] as the only way to call your function and let the caller call you function as do_stuff([x]) if they only have a single item x. The IDE will complain instantly if you try to call it as do_stuff(x) so there is no risk to accidentally call it like that.
At runtime. In production. A compiler would catch the problem at build time, never causing an error in production.
And a nice IDE/code editor would catch the problem as you're typing it
Also, error messages in an IDE can be ignored. Compiler errors can’t.
> So of course you actually need to exercise the code also, which is where the hypothesis package comes in.
These are tests you should be doing anyway. Type checking does not excuse poor test coverage.
That cannot be because of missing types. If you make just 500 lines python unmaintainable you're just a terrible programmer! In it's core it cannot be a type problem. And that is my main point here; there is a hype going on in the dynamic languages to add types, as if it solves everything. IMHO it's not that simple.
To avoid unnecessary explanation about the value of static typing; I am not against, I'm doing c++ and it serves me well.
The absolute horror it will be to debug this mess when people starts to use it, my god.
Another problem with Python is that the culture of testing is definitely not as strong as in Ruby so you won't even get that to compensate the untyped nature of the language.
So the type of almost any class is really more like Struct{WhatYouThinkTheClassIs; ArbitraryDict;} ... and the temptation to misuse this, say for instance if you don't want to add arguments to function_used_lots_of_places(some_object), can be huge. And more generally, this openness means that there may be discrepancies between what's unit tested for a class, and how that class is used in the wild.
But I've seen a frustrating trend recently. Where companies on languages like C#/Java. With a massive code base are moving to Python. I often get recruiter calls to lead a new python team, transitioning away from (Java/C#/etc).
The sole reason, is it takes to long to develop a feature in the legacy language. Which is resultant of outdated software and practices. I generally try and steer them towards CI/CD and newer lighter frame works. But someone way up heard python was the hot new thing. Now all critical back-end services must be in python.
To add to this I pushed for type hinting. But type hinting will "slow down developers". Part of the problem to me, at least. Is the person dictating development frameworks, languages, etc. Isn't really a coder, and heard about thing X at some conference.
I like python, but it's an infrastructure quick scripting language. Additionally a lot of the good python devs I know shifted over to tensor flow and machine learning.
For the past week I've been updating a (much shorter) solo app, written in a statically-typed language, and having a bear of a time getting the compiler to stop throwing false type errors at me. Yes, it's the stable release version of the compiler. That has never stopped any compiler from shipping with bugs. These type inference systems can be pretty complex.
Then again, I seem to run into more compiler bugs in general than anyone I know. How do you all do it?
Interesting analogy, but in my experience it doesn't hold up.
If you have a Python typing bug, it will crash your program almost immediately and you can quickly catch it and fix it. In contrast, C boundary checking issues often come up in relatively rare corner cases, and when they do occur, they often do not result in an exception / error especially if the memory is already paged and set to zero.
In production code, boundary checking errors in C occur all the time, but Python type bugs are pretty rare.
People can change unit tests. The benefit of this, is it's a kind of documentation. People can see the tests and know how it _should_ work, or they can not read them and if they create errors, they'll find out the hard way. Unit tests don't make a specification static, but they do reduce chaos.