How to make a python listener&talker on the same node?

edit

There is no magic trick to make this work, you just initialize both after you have called rospy.init_node(...) (Edited in response to your comment)

import rospy
from std_msgs.msg import String
rospy.init_node("One_node_to_rule_them_all")
pub = rospy.Publisher("echo", String)

def callback(input):
        pub.publish(input.data)
        # The message has 2 parts, a header and the data. We only want to use the actual data

sub = rospy.Subscriber("chatter", String, callback)

pub2 = rospy.Publisher("chatter", String)
pub2.publish("'Stop repeating everything I say")

When you run rostopic echo /echo It will show the desired output