[Python] Custom ValidationError message for extra fields

I have defined a model using Pydantic V2 as follows:

from pydantic import BaseModel

class Data(BaseModel):
valid: bool = False
name: str | None = None
model_config = ConfigDict(extra="forbid")


When I use this model to validate some data using model_validate with some extra field

Data.model_validate({"valid": True, "name": "John", "age": 30})


It raises this expected error:

pydantic_core._pydantic_core.ValidationError: 1 validation error for Data
age
Extra inputs are not permitted [type=extra_forbidden, input_value=30, input_type=int]
For further information visit https://errors.pydantic.dev/2.10/v/extra_forbidden


What I want to do is to replace the default message Extra inputs are not permitted by a custom message Unknown field.. To do so, I overwrote the model_validate method so I can customize my message. My model is defined now as follows:

from pydantic import BaseModel, ConfigDict
from pydantic_core import InitErrorDetails, ValidationError

class Data(BaseModel):
valid: bool = False
name: str | None = None
model_config = ConfigDict(extra="forbid") # Forbid extra fields

@classmethod
def model_validate(cls, value):
try:
return super().model_validate(value)
except ValidationError as e:
modified_errors = []
for error in e.errors():
if error['type'] == 'extra_forbidden':
modified_errors.append(
InitErrorDetails(
type=error['type'],
loc=error['loc'],
input=error['input'],
ctx={"error": "Unknown field."} # Set custom message in `ctx`
)
)
else:
modified_errors.append(error)

raise ValidationError.from_exception_data(
title="Validation failed",
line_errors=modified_errors
)


But, still when I run Data.model_validate({"valid": True, "name": "John", "age": 30}). It does not show the custom message "Unknown field.". What's wrong with my validator?

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