Decodes base64 value and set the file object

def set(self, instance, value, **kw):
        """Decodes base64 value and set the file object
        """
        value = str(value).decode("base64")

        # handle the filename
        if "filename" not in kw:
            logger.debug("FielFieldManager::set: No Filename detected "
                         "-> using title or id")
            kw["filename"] = kw.get("id") or kw.get("title")

        self._set(instance, value, **kw)