How to use the nassl._nassl.WantReadError function in nassl

def do_handshake_with_heartbleed(self):
    # This is nassl's code for do_handshake() modified to send a heartbleed
    # payload that will send the heartbleed checking payload
    # I copied nassl's code here so I could leave anything heartbleed-related
    # outside of the nassl code base
    try:
        if self._ssl.do_handshake() == 1:
            self._handshakeDone = True
            return True # Handshake was successful

    except WantReadError:
        # OpenSSL is expecting more data from the peer
        # Send available handshake data to the peer
        # In this heartbleed handshake we only send the client hello
        lenToRead = self._networkBio.pending()
        while lenToRead:
            # Get the data from the SSL engine
            handshakeDataOut = self._networkBio.read(lenToRead)
            # Send it to the peer
            self._sock.send(handshakeDataOut)
            lenToRead = self._networkBio.pending()

        # Send the heartbleed payload after the client hello
        self._sock.send(heartbleed_payload(self.sslVersion))

        # Recover the peer's encrypted response
        # In this heartbleed handshake we only receive the server hello