def _is_on_symbol(self, offset):
        "Is this offset on a symbol?"
        if not ROPE_AVAILABLE:
            return False
        data = self.resource.read()
        if offset >= len(data):
            return False
        if data[offset] != '_' and not data[offset].isalnum():
            return False
        word = worder.get_name_at(self.resource, offset)
        if word:
            return True
        else:
            return False
Is this offset on a symbol?