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Comment by veber-alex | Hacker News Reader

Well on Pycharm 2022.3 which is what I still have installed even this simple function doesn't show any error.

  def foo() -> int:
      pass

I sure hope they improved the type checker in later versions...

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On the other hand, Pycharm will show an error if you replace the pass keyword with any statement. Seems like a deliberate behavior - it declines to typecheck a stub.

Um lol what do you think the error is here? This is widely accepted syntax for a stub. So yes it does return None if run but it's not expected to ever be run. So pretty ironic that you would blame pycharm (which is indeed excellent) for your own misunderstanding.

https://mypy.readthedocs.io/en/stable/stubs.html#using-stub-...

> Um lol what do you think the error is here? This is widely accepted syntax for a stub.

No it isn't. The accepted stub syntax is an ellipses (...).

A competent type checker like pyright will error on this code.

  Function with declared return type "int" must return value on all code paths
    Type "None" cannot be assigned to type "int"

And if you need more proof that pycharm is useless as a type checker:

  def foo(b) -> int:
      if b:
          return 1

A classic error where you forget to return a value from all paths and pycharm is silent.

I linked directly to the section of mypy docs that shows you are wrong - all you have to do is click the link to understand that you are wrong:

>(Using stub file syntax at runtime). You may also occasionally need to elide actual logic in regular Python code... You can also elide default arguments as long as the function body also contains no runtime logic: the function body only contains a single ellipsis, the pass statement, or a raise NotImplementedError(). It is also acceptable for the function body to contain a docstring. For example:

And why would I care about mypy docs? pyright does the correct thing by showing an error.

In any case, the second example is definitely not a stub.

this is the weirdest "head in sand" moment; you literally called out mypy as a desirable alternative

>And to add insult to injury Pycharm doesn't even have a pyright plugin and the mypy plugin is extremely slow and buggy.

ie you recognize that aligning with mypy is desirable.

That’s not a type error in python. All types in puthon (afaik) accept ‘None’ as a value.

For example, try:

   a : int = None

It will succeed. This is done (I think) so you can tell whether optional arguments are defined, declare variables before use (eg if you have a conditional with two branches both setting a different value for a variable sibce python blocks aren’t expressions) and that kind of thing.

Each type checker can implement however strict rules it wants. And pyright gives the correct answer here:

  Expression of type "None" cannot be assigned to declared type "int"
    Type "None" cannot be assigned to type "int"

It's not recommended anymore. Optional types should be explicit. https://peps.python.org/pep-0484/#union-types

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