communicating with serial virtual COM port using python

Question

I have written snippet below to communicate (send a simple '1' character) with serial virtual COM3 port, which is connected to a STM32 board, using python. But the code does not works. I should also mention that by using Terminal app, I can send and receive data to COM port. The figure shows the setting in Terminal app: Terminal setting

The code is as follows:

@pyqtSlot() # the snippet is part of a pyqt5 code.
def on_click(self):
    print("here")
    ser = serial.Serial('COM3', 115200, timeout = 1, bytesize = serial.EIGHTBITS, parity = serial.PARITY_NONE, stopbits = STOPBITS_ONE)
    ser.open()
    ser.write('1') #I used also ser.write('1'.encode('UTF-8'))
    ser.close()

Thanks for your time.