arm.py

# Import mavutil
from pymavlink import mavutil
import time

# Create the connection
master = mavutil.mavlink_connection('udpin:0.0.0.0:15000')
# Wait a heartbeat before sending commands
master.wait_heartbeat()

# Arm
# master.arducopter_arm() or:
master.mav.command_long_send(
    master.target_system,
    master.target_component,
    mavutil.mavlink.MAV_CMD_COMPONENT_ARM_DISARM,
    0,
    1, 0, 0, 0, 0, 0, 0)