Can't figure out the syntax for Optional[T] to use with dataclasses

[vidjuheffex]

From what I gather this looks correct:

(defclass [dataclass] MyClass []
  "A dataclass to hold round information"
  #^ (of Optional int) myattr None)

If I evaluate that it evaluates with no issue

if I make (MyClass) it complains about the positional argument myattr being missing, but it's optional and has an Assignment?

[Kodiologist]

What would be the Python equivalent of the desired Hy code?

[vidjuheffex]

from dataclasses import dataclass
from typing import Optional

@dataclass
class MyClass:
    myattr: Optional[int] = None

so MyClass can be made with simply (MyClass)

[Kodiologist]

In that case, Sunjay's answer should have you covered.

[scauligi]

hy --spy (or hy2py) is your friend!
The #^ macro doesn't generate an assignment, it's just the annotation; you still need a setv. So your current Hy code declares a field myattr with no assignment, followed by a standalone expression None:

# => (defclass [dataclass] MyClass []
# ...   "A dataclass to hold round information"
# ...   #^ (of Optional int) myattr None)
@dataclass
class MyClass:
    """A dataclass to hold round information"""
    myattr: Optional[int]
    None

You probably want this:

(defclass [dataclass] MyClass []
  (setv #^ (of Optional int) myattr None))

which translates to this:

@dataclass
class MyClass:
    myattr: Optional[int] = None

[vidjuheffex]

Oh wow, thank you!!