Using global variables with a subscriber

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Below is my code:

if __name__ == "__main__":
    rospy.init_node("robot_control_node", anonymous=True)
    rospy.Subscriber("/rx150/joint_states", JointState, get_arm_pose)

def get_arm_pose(data):
    global waistp, shoulderp, elbowp, waistv, shoulderv, elbowv
    waistp = math.degrees(data.position[5]) + 180
    shoulderp = abs(math.degrees(data.position[4]) - 90)
    elbowp = abs(math.degrees(data.position[0]) - 90)
    waistv = data.velocity[5]
    shoulderv = data.velocity[4]
    elbowv = data.velocity[0]

def simulate(episode, is_training):
    global waistp, shoulderp, elbowp, waistv, shoulderv, elbowv
    reward = 0
    max_step = 20
    is_done = False
    episode_reward = 0
    x_target = math.cos(math.radians(episode * 6)) * 200
    y_target = math.sin(math.radians(episode * 6)) * 200
    z_target = 250
    waist_force = 0
    shoulder_force = 0
    elbow_force = 0
    for step in range(max_step):
        next_obs[0] = waistp

It shows the following error:

NameError: name 'waistp' is not defined