In a pydantic model, how do I define the type of property which is a decorated method?

Question

Consider this code snippet:

from pydantic import BaseModel

class SomeModel(BaseModel):
    property_1: str
    property_2: Dict[str, str]
    property_3: int = 12

    @property
    def property_4(self) -> int:
        response = external_call()  # returns '22.0' (a string)

>>> a = SomeModel(property_1="a", property_2={"k": "v"}, property_3="12.0")
>>> a.property_3
12
>>> a.property_4
'22.0'

property_3 gets properly casted to int. How do I achieve the same with the @property decorator? Is it possible to get pydantic do its magic on those decorated properties?

Answer 1

My Answer

You can use pydantic.validate_call to cast the property: https://docs.pydantic.dev/latest/concepts/validation_decorator/

My Example

from pydantic import VERSION, BaseModel, validate_call


print(VERSION)
# > 2.0.3


class SomeModel(BaseModel):
    property_1: str
    property_2: dict[str, str]
    property_3: int = 12

    @property
    @validate_call(validate_return=True)  # and cast by type annotation
    def property_4(self) -> int:
        return '22.0'


a = SomeModel(property_1="a", property_2={"k": "v"}, property_3="12.0")
print(a.property_4, type(a.property_4))
# 22 <class 'int'>