UART send no bytes

Question

I'm trying to write test code for sending data via UART on my Raspberry PI 3 b+ , but I cannot receive back the data I've sent . Raspberry is connected via UART module to my laptop , so I can see in Putty results. Anyone can tell me what Am I doing wrong?

I've checked if port isOpen and it returned True , msg=b'Hello' returned Hello showed hello , but no bytes received . Sending single bytes give also no bytes detected . Erasing the timeout showed that it is reached.

Edit: did little testing if port's are working properly

from __future__ import print_function
import serial

test_string = "Testing 1 2 3 4".encode('utf-8')
#test_string = b"Testing 1 2 3 4" ### Will also work

port_list = ["/dev/serial0", "/dev/ttyS0"]

for port in port_list:

    try:
        serialPort = serial.Serial(port, 9600, timeout = 2)
        serialPort.flushInput()
        serialPort.flushOutput()
        print("Opened port", port, "for testing:")
        bytes_sent = serialPort.write(test_string)
        print ("Sent", bytes_sent, "bytes")
        loopback = serialPort.read(bytes_sent)
        if loopback == test_string:
            print ("Received", len(loopback), "valid bytes, Serial port", port, "working \n")
        else:
            print ("Received incorrect data", loopback, "over Serial port", port, "loopback\n")
        serialPort.close()
    except IOError:
        print ("Failed at", port, "\n")

That give me information that tty0 is not working properly but , also got absolutly no answer about correctness on port serial0

import serial
import struct
import time

port = serial.Serial("/dev/ttyS0", baudrate=115200, timeout=2.0)

i = 0
while True:
    msg = struct.pack('>HBBB', 3000, 243, 234, 254)
    port.write(msg)
    time.sleep(0.3)

    bytesToRead = port.inWaiting()
    print("Found {} bytes in serial".format(bytesToRead))
    if bytesToRead == 5:
        rcv = port.read(5)
        # port.write('\r\nYou sent:' + repr(rcv))
        for i in range(5):
            print('\r {} - {}'.format(i, bytes(rcv[i])))

        idCode = struct.pack('BB', rcv[0], rcv[1])
        idCode = struct.unpack('>H', idCode)
        idCode = idCode[0]
        # value = struct.unpack_from('HBBB', decode)
    i += 1
    if i == 4:
        exit()

Expected Results:

Found 5 bytes in serial

(index) - (byte at that index)

Got:

Found 0 bytes in serial

Answer 1

Solved. It was just matter of wiring . If someone in future would like to run test like that - they must remember to connect RX with TX line . Or if it connected with laptop there's it should be better to create code responsible for communication on it (but instead of ttyS0 or Serial0 , port should be set to proper COM e.g. "COM3")