'Return the DER encoding for the ASN.1 SEQUENCE, containing
the non-negative integers and longs added to this object.
Limitation: Raises a ValueError exception if it some elements
in the sequence are neither Python integers nor complete DER INTEGERs.'

def encode(self):

    self.payload = b('')
    for item in self._seq:
        try:
            self.payload += item
        except:
            try:
                self.payload += DerInteger(item).encode()
            except:
                raise ValueError('Trying    to    DER    encode    an    unknown    object')
    return DerObject.encode(self)
