Python docstring type annotation -- a class, not an instance?

Question

Let's say I have:

class A(object):
   pass

class B(A):
   pass

I want to declare a function that takes a subclass of A as an argument:

def do_something(klass):
   """
   :type klass: WHAT_HERE
   """
   pass

What should I put in WHAT_HERE? If I make this:

:type klass: A

PyCharm thinks that I should give an instance of A as an argument, not the class itself.

Answer 1

According to the pycharm docs as close as you can get is:

() -> SomeClass

So in your example

def do_something(klass):
   """
   :type klass: () -> A
   """
   pass

This means (for PyCharm) that the argument you are providing is a function that returns an object of a given type. It will properly type hint anything after the object creation.

Answer 2

Guido answered this question here, but I believe PyCharm does not correctly support the appropriate syntax in Python 2. I believe the syntax should be (...) -> A in PyCharm with Python 2. In Python 3, the appropriate syntax is Callable[..., A].

I note that PyCharm doesn't treat () -> A as a class either; if you call a classmethod on A using this syntax, PyCharm inspection will flag that it can't find the referenced classmethod.

This has been filed in the JetBrains bugtracker, though was closed based on earlier comments. Given Guido's recent comments in the first reference, I'm hoping JetBrains will reopen.