Dronekit Script Not Connecting

This is the script I am running to connect to a drone with px4 autopilot with a USB cable in com4.

from dronekit import connect

vehicle = connect(‘com4’, wait_ready=True)
print(“connection command run”)

This is the error it continually throws:

Traceback (most recent call last):
File “C:/Users/ethan/project/DroneKit Test.py”, line 6, in
vehicle = connect(‘com4’, wait_ready=True)
File “C:\Python27\lib\site-packages\dronekit_init_.py”, line 3159, in connect
handler = MAVConnection(ip, baud=baud, source_system=source_system, source_component=source_component, use_native=use_native)
File “C:\Python27\lib\site-packages\dronekit\mavlink.py”, line 130, in init
self.master = mavutil.mavlink_connection(ip, baud=baud, source_system=source_system, source_component=source_component)
File “C:\Python27\lib\site-packages\pymavlink\mavutil.py”, line 1777, in mavlink_connection
File “C:\Python27\lib\site-packages\pymavlink\mavutil.py”, line 935, in init
import serial
ImportError: No module named serial

I would really appreciate your help with this. I have been stuck at trying to connect to my drone for over a month. Also, if you have an alternative to dronekit that could you point me in the right direction and maybe include sample code to connect to the drone? Thank you!