How can I generate a UUID in a Pydantic BaseModel subclass?

My code looks a bit like this:

class Error(BaseModel):
     id: uuid.UUID
     code: int

     def __init__(self, code: int) -> None:
        self.id = uuid.uuid4()
        self.code = code

        super().__init__(id=self.id, code=code)

This errors out with:

AttributeError: ‘Error’ object has no attribute ‘pydantic_fields_set‘

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I just don’t want to have the boilerplate of generating the UUID each time I create a new Error(), plus… it should be the Error class’ responsibility to instantiate its own UUID.

I’m not sure what I’m doing wrong.

>Solution :

Use Field(default_factory=...):

import uuid

import pydantic


class Error(pydantic.BaseModel):
    id: uuid.UUID = pydantic.Field(default_factory=uuid.uuid4)
    code: int


print(Error(code=123))
print(Error(code=456))

prints out

id=UUID('dfe3052b-e8bc-4c8b-9f45-d51d2c8c412c') code=123
id=UUID('b66ba637-6734-47cf-aa91-540306918efe') code=456