Common validator for use in both rest framework serializers and django forms. Support overriding for default error messages and error field representation

django-validator-for-serializer-and-form.py

class Validator(object):
    """
    Validator for validate data, 
    which used for both rest framework serializers and django forms.
    Support binding error message for several fields 
    if you override default error fields and set value as tuple.
    """

    default_error_messages = {
        "field1": "This field is required",
    }
    default_error_fields = {
        "field1": "represent_field1"
    }

    def __init__(self, error_messages=None, error_fields=None):
        error_messages = error_messages or {}
        error_fields = error_fields or {}

        self._errors = defaultdict(list)

        self._error_messages = self.default_error_messages.copy()
        self._error_messages.update(error_messages)

        self._error_fields = self.default_error_fields.copy()
        self._error_fields.update(error_fields)

    @property
    def error_messages(self):
        return self._error_messages

    @property
    def error_fields(self):
        return self._error_fields

    @property
    def errors(self):
        return self._errors

    def add_error(self, key):
        field = self.error_fields[key]
        msg = self.error_messages[key]

        if isinstance(field, tuple):
            for f in field:
                self._errors[f].append(msg)
        else:
            self._errors[field].append(msg)

    def validate_field1(self, value):
        if not value:
            self.add_error("field1")