I am writing a script to post data from an internal system to a third party web API. Our internal system uses data Models defined in Pydantic. I am trying to send data in one of these models to the API using requests.post but it can’t serialize some types and it’s driving me insane.

Take this data model as an example:

class Product(BaseModel):
    id: int
    group_id: int
    sku: str
    price: Decimal
    special_offer_price: Decimal
    last_update: datetime.date

If I try to send data using this Model using requests.post thus:

product_item = website_api.Product(**product.__dict__)

requests.post(url, headers=jwt_auth.auth_header, json=product_item)

The str and int fields are fine but Decimal and datetime.date fields throw up an exception as they are not serializable, giving the error somewhat like:

TypeError: Object of type date is not JSON serializable

I have tried adding a @field_serializer for the fields to the class definition for pydantic;

    @field_serializer("price", "special_offer_price")
    def serialize_decimal(self, value):
        return str(value)
    
    @field_serializer("last_update")
    def serialize_date(self, value):
        return str(value)

but requests doesn’t seem to use it when serializing.