Pydantic Model Field Of Type Union[int, float] : How To Prevent Field From Rounding To int When Initialised With float Value?

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I have the following pydantic model which contains a result typed as Union[int,float] as listed below.

from typing import Union

from pydantic import BaseModel


class Calculation(BaseModel):
    arg1: int 
    arg2: int 


class CalculationResult(Calculation):
    op: str 
    result: Union[int, float]


if __name__ == "__main__":

    arg1 = 1 
    arg2 = 2 
    result = arg1 / arg2

    # this displays type of result := <class 'float'> when program is run
    print(f"type of result := {type(result)}")

    x = CalculationResult(**{"arg1": arg1, "arg2": arg2, "op": "divide", "result": result}) 

    print(f"result := {x.result}")

When the result property of CalculationResult has a value of 0.5 it is rounded to 0.

How do I get pydantic to recognise that 0.5 is a float for the typing hint Union[int, float]?

pydantic python-3.x
1 Answers

Solved after looking at Pydantic documentation!

The solution is to specify the most specific type first, followed by less general types. In this case, I swapped the order of float and int in the union type declaration.

class CalculationResult(Calculation):
    op: str 
    result: Union[float, int]
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