Was battling it today. Latest stable release of python mind you 3.7.3. We have t...

emptysea · on Aug 29, 2019

I agree that mypy can be a bit lacking, but to address a couple of your mypy woes:

- TypedDict is an option but if you can, dataclasses work much better

- mypy does refine Optional[T] to T with an if check. Maybe you need to futz with the compiler options?

- Does Literal["foo"] not work? I've been using it with pydantic for de-serializing a tagged union of dicts and also for function args.

e.g.,

    def call_to_service(api_type: Literal["users", "teams", "orgs") -> None: ...

penagwin · on Aug 29, 2019

The problem I had with Literal["foo"] is that at least according to mypy "foo" is a string and it was expecting Literal["foo"].

I think you're right, something must be mixed up. But then again this is the latest version of python and mypy, on intellij, so I'm not sure what I did wrong, it's using otherwise default options.

mijamo · on Aug 29, 2019

That is false.

On point 1: def use_int(n: int): return n * 2

  def foo(n: Optional[int]):
      use_int(n) # MYPY complaints here because n could be None
      if n is not None:
          use_int(n) #MYPY allows this because it understood it cannot be None

2) TypeDict work fine, do you have an example of waht does not work 3) Of course, JS is different from Python, "keyof" doesn't make any sense in Python because Python uses class where JS uses dicts 4) Of course there is:

  Accepted = Literal["foo", "bar", 3]
  
  def accept_values(v: Accepted):
      print(v)
  
  accept_values("foo")
  accept_values("bar")
  accept_values(3)
  accept_values("wrong")  # MYPY complains
  accept_values(5)  # MYPY complains

Rotareti · on Aug 30, 2019

> "I'm familiar with tool A. Today I tried tool B and I couldn't figure out how to use it correctly, so it must be lacking. Everyone should know!"

From the points you make it seem like you haven't really figured out how to use mypy...

TS and Python/Mypy are my daily drivers. I don't find the experience working with mypy any worse than working with TS. In fact I prefer composing and consuming types via dataclasses and NamedTuples over interfaces and TS classes.