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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_valid(self):
 """ Validates single instance. Returns boolean value and store errors in self.errors """

        self.errors = []

        for field in self.get_all_field_names_declared_by_user():
            getattr(type(self), field).is_valid(self, type(self), field)
            field_errors = getattr(type(self), field).errors(self)
            self.errors.extend(field_errors)

        return len(self.errors) == 0