ValueError: "port" must be None or a string, not <class 'int'>

I am trying to issue commands to my usb connected lock controller. The code runs fine until this line:

Connected ports: 
['COM6']
Please enter the port number that has port connected. 
 i.e. if COM3 is shown, enter 3 when ask to enter port number. 
 If the above shows [] than no connected port is found and errors will follow
Please enter the port number: 6

and the following error came up:

ValueError: "port" must be None or a string, not <class 'int'>

I get the following error:

Traceback (most recent call last):
  File "[...]", line 44, in <module>
    serial_connection() #executes the function defined above

  File "[...]", line 29, in serial_connection
    ser.port = COMPORT - 1 #counter for port name starts at 0

  File "[...]", line 260, in port
    raise ValueError('"port" must be None or a string, not {}'.format(type(port)))

Below is the code:

#this library is required as it helps establish the serial connection
#Using  pyserial Library to establish connection
import serial #not being used because it was already called in portRead
from portRead import *

#Global Variables
ser = 0

#this will print out the port that can be used; ports that are connected. i.e. if COM3 is shown, enter 3 when ask to enter port number
#if shown [] then no usb is connected to a port and errors will follow
if __name__ == '__main__':
    print ("Connected ports: ") #print means printing information on screen
    print(serial_ports()) #function derived from portRead
    print("Please enter the port number that has port connected. n "
          "i.e. if COM3 is shown, enter 3 when ask to enter port number. n If the above shows [] than no connected port is found and errors will follow")

#defining the serial connection
def serial_connection():
    while True: #the while loop is used to continuously ask you to issue a new command until you decide to quit the program
        ser = serial.Serial()
        ser.baudrate = 38400 #Suggested rate in Southco documentation, both locks and program MUST be at same rate
        COMPORT = int(input("Please enter the port number: ")) #this refers to which port your usb is inserted into
        ser.port = COMPORT - 1 #counter for port name starts at 0

        print ('Port %d entered Stephan '%COMPORT)
        #timeout in seconds
        ser.timeout = 10
        ser.open()
        command = input("please type command - open1/close1, or open2/close2. n"
                    "If already open and you try to open no action will be taken and vice-versa...: n ")
        #call the serial_connection() function
        ser.write(("%srn"%command).encode('ascii')) #Southco locks receives and sends commands in ASCII


serial_connection() #executes the function defined above