Send Rc to Pixhawk

Hello friends,I want to send rc values to Pixhawk from Raspberry Pi,I found this code but ı want to serial communication instead of Udp how can ı change this code thanks a lot

# Import mavutil
from pymavlink import mavutil

# Create the connection
master = mavutil.mavlink_connection('udpin:')
# Wait a heartbeat before sending commands

# Create a function to send RC values
# More information about Joystick channels
# here:
def set_rc_channel_pwm(id, pwm=1500):
    """ Set RC channel pwm value
        id (TYPE): Channel ID
        pwm (int, optional): Channel pwm value 1100-1900
    if id < 1:
        print("Channel does not exist.")

    # We only have 8 channels
    if id < 9:
        rc_channel_values = [65535 for _ in range(8)]
        rc_channel_values[id - 1] = pwm
            master.target_system,                # target_system
            master.target_component,             # target_component
            *rc_channel_values)                  # RC channel list, in microseconds.

# Set some roll
set_rc_channel_pwm(2, 1600)

# Set some yaw
set_rc_channel_pwm(4, 1600)

# The camera pwm value is the servo speed
# and not the servo position
# Set camera tilt to 45º with full speed
set_rc_channel_pwm(8, 1900)