Writing commands to serial

[python_beginner]

Thank you, I managed to make it send command, but not to make the

        out = ser.read()
        print('Receiving...'+out)

work. What I am trying to do is this: I wrote a code to read from Arduino through Serial, and I want to send commands to the Arduino through serial (by typing the commands through the keyboard). The code I am using is this:

import serial,time
ser = serial.Serial(
    port='COM4',
    baudrate=38400,
    bytesize=serial.EIGHTBITS,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    xonxoff=False
)
line = ser.readline();

while line:
     line = ser.readline()
     print(line)
     ser.reset_input_buffer()
     cmd = input("Enter command or 'exit':") + '\r\n'
     if len(cmd)>0:
        ser.write(cmd.encode())
     else:
        continue

but what I see is that the code blocks, until I print something. I want to read continuously from Serial what Arduino sends and if I type a command from keyboard, to write it to the serial. I am trying changes and I read the pyserial documentation but I cannot figure out something...