I want to use Pydantic to validate fields in my object, but it seems like validation only happens when I create an instance, but not when I later modify fields.

from pydantic import BaseModel, validatorclass MyStuff(BaseModel):name: str@validator("name")def ascii(cls, v):assert v.isalpha() and v.isascii(), "must be ASCII letters only"return v# ms = MyStuff(name = "[email protected]")   # fails as expected
ms = MyStuff(name = "me")
ms.name = "[email protected]"
print(ms.name)   # prints [email protected]

In the above example, Pydantic complains when I try to pass an invalid value when creating MyStuff, as expected.

But when I modify the field afterwards, Pydantic does not complain. Is this expected, or how can I have Pydantic also run the validator when assigning a field?

This is the default behavior. To enable validation on field assignment, set validate_assignment in the model config to true:

class MyStuff(BaseModel):name: str@validator("name")def ascii(cls, v):assert v.isalpha() and v.isascii(), "must be ASCII letters only"return vclass Config:validate_assignment = True