How can I customize error messages of Cerberus?

Question

I want to localize the error messages Cerberus returns, e.g. I'd like to achieve the following:

>>> validator.schema = {'animal': {'forbidden': ['Einhorn']}}
>>> validator({'animal': 'Einhorn'})
False
>>> validator.errors
{'animal': ['VERBOTEN!']}  # instead of 'unallowed value Einhorn'

Answer 1

You can simply subclass the default error handler BasicErrorhandler from the cerberus.errors module and adjust the message templates as you like:

>>> class CustomErrorHandler(errors.BasicErrorHandler):
...     messages = errors.BasicErrorHandler.messages.copy()
...     messages[errors.FORBIDDEN_VALUE.code] = 'VERBOTEN!'
...     
>>> validator = Validator(schema, error_handler=CustomErrorHandler)
>>> validator({'animal': 'Einhorn'})
False
>>> validator.errors
{'animal': ['VERBOTEN!']}

Have a look at the source code for available error codes and template variables.