Validate class attributes when overwriting using pydantic

Question

I am using Pydantic to validate my class data. In some cases after the class has been instantiated, I want to overwrite the value of a field, but I want to verify that the new value has the same type as defined in the Model . I expect I should be able to use validators but I haven't seen an option for protecting the field after the object is created.

Is there a simple mechanism within pydantic which allows this type of validation?

Example

from pydantic import BaseModel, validator

class MyModel(BaseModel):
    some_field : str = None
        
    @validator("some_field")
    def verify_string(cls, v):
        print(f"Verifying some_field value: {v}")
        if not isinstance(v, str):
            raise ValueError(f"some_field must be str; got type {type(v)}")
        return v

# Instantiate model
m = MyModel(some_field = "test")
## prints: Verifying some_field value: test
print(m.some_field)
## prints: test


# Overwrite a field within invalid type
m.some_field = 100 # <-- this should raise value error
print(m.some_field)
## prints: 100

Answer 1

Sorry I found the solution -- use Config and some validator parameters.

class MyModel(BaseModel):
    some_field : str = None

    class Config:
        validate_assignment = True   
     
        
    @validator(
        "some_field", always=True, pre=True,
    )
    def verify_string(cls, v):
        print(f"Verifying some_field value: {v}")
        if not isinstance(v, str):
            raise ValueError(f"some_field must be str; got type {type(v)}")
        return v