python to make a bot run around

bot.py

import time

import math as m
import socket
import RPi.GPIO as GPIO

# import RPi.GPIO

pin_motor_1_a = 21  # GPOIO38
pin_motor_1_b = 20  # GPIO40

pin_motor_2_a = 18  # GPIO12
pin_motor_2_b = 23  # GPIO16

speed = 35


def stop():
    print("stop")
    motor_a[0].ChangeDutyCycle(0)
    motor_a[1].ChangeDutyCycle(0)
    motor_b[0].ChangeDutyCycle(0)
    motor_b[1].ChangeDutyCycle(0)


def forward():
    stop()
    print("foward")
    motor_b[0].ChangeDutyCycle(speed+20)
    motor_b[1].ChangeDutyCycle(0)


def reverse():
    stop()
    print("reverse")
    motor_b[0].ChangeDutyCycle(0)
    motor_b[1].ChangeDutyCycle(speed+20)


def left():
    stop()
    print("left")
    motor_a[0].ChangeDutyCycle(0)
    motor_a[1].ChangeDutyCycle(speed)

def right():
    stop()
    print("right")
    motor_a[0].ChangeDutyCycle(speed)
    motor_a[1].ChangeDutyCycle(0)

if __name__ == '__main__':
    print("ok 2")
    print(m.pi)
    print(socket.gethostname())

    GPIO.setwarnings(False)
    GPIO.setmode(GPIO.BCM)

    GPIO.setup(pin_motor_1_a, GPIO.OUT)
    GPIO.setup(pin_motor_1_b, GPIO.OUT)
    motor_1_f = GPIO.PWM(pin_motor_1_a, 1000)
    motor_1_r = GPIO.PWM(pin_motor_1_b, 1000)
    motor_1_f.start(0)
    motor_1_r.start(0)
    motor_a = [motor_1_f, motor_1_r]

    GPIO.setup(pin_motor_2_a, GPIO.OUT)
    GPIO.setup(pin_motor_2_b, GPIO.OUT)
    motor_2_f = GPIO.PWM(pin_motor_2_a, 2000)
    motor_2_r = GPIO.PWM(pin_motor_2_b, 2000)
    motor_2_f.start(0)
    motor_2_r.start(0)
    motor_b = [motor_2_f, motor_2_r]

    time.sleep(1)

    forward()
    time.sleep(2)

    left()
    time.sleep(2)

    reverse()
    time.sleep(2)

    right()
    time.sleep(2)

    print("done")