Calculation fails on dates

[emilzak]

The problem
I created two user-defined functions, BSDATE and BSNUMBER. BSDATE returns datetime.date and BSNUMBER returns int.
Operations performed on numbers work well. Ops on dates fail with #VALUE!

I've attached the excel and python code.

Please look at D1 (Error) and D2 ( Success )

import datetime
import formulas

def _BSDATE(m):
	return datetime.date(2024,m,30)
def _BSNUMBER(n):
	return n

FUNCTIONS = formulas.get_functions()
FUNCTIONS["BSDATE"] = _BSDATE
FUNCTIONS["BSNUMBER"] = _BSNUMBER

xl_model = formulas.ExcelModel().loads("333.xlsx").finish()
xl_model.calculate()
xl_model.write(dirpath="output")

Python: 3.8
OS: macOS Sonoma

Here is the result of the calculation

Please advise, and thanks for your work!

333.xlsx

UPDATE 1:

1. I tried to return formatted string from _BSDATE function - same result
2. If i set a string value instead of the function _BSDATE in the excel calculation works correctly