field.py

def run_validators(self, value):
    if value in self.empty_values:
        return

    errors = []
    for v in self.validators:
        try:
            v(value)
        except exceptions.ValidationError as e:
            if hasattr(e, 'code') and e.code in self.error_messages:
                e.message = self.error_messages[e.code]
            errors.extend(e.error_list)

    if errors:
        raise exceptions.ValidationError(errors)

def clean(self, value, model_instance):
    """
    Convert the value's type and run validation. Validation errors
    from to_python() and validate() are propagated. Return the correct
    value if no error is raised.
    """
    value = self.to_python(value)
    self.validate(value, model_instance)
    self.run_validators(value)
    return value