Run code on pressing a key in Pythonaddins

Question

I tried making an addin having below code where I want the user to press a predefined key and the "required_code" should run on the selected features.

import arcpy
import pythonaddins

class Key1(object):
    """Implementation for Key Listener_addin.Key1 (Button)"""
    def __init__(self):
        self.enabled = True
        self.checked = False
    def onKeyUp(self, keycode, shift):
        print("Process Started")
        print("Key pressed: " + keycode)
        self.checked = True
        #required_code goes here with messagebox
        print("Process Completed")
        self.checked = False

However The above code doesn't do anything, not even printing first line.

How could I enable this addin to run the code on pressing a key? Also how can I print which key is pressed by user?

Could you correct me on what I am doing wrong?

UPDATE:

I have tried to define keycode using msvcrt but it is still not working. My updated code is:

import arcpy
import pythonaddins
from msvcrt import getch

class Key1(object):
    """Implementation for Key_Listener_addin.Key1 (Button)"""
    def __init__(self):
        Key1.enabled = True
        Key1.checked = False
        keycode = msvcrt.getch()
    def onClick(self):
        if Key1.checked == True:
            Key1.checked = False
        elif Key1.checked == False:
            Key1.checked = True
    def onKeyUp(self, keycode, shift):
        if Key1.checked == True:
            if keycode == 85:
                print(keycode)

85 is the ASCII value for 'U'.

Answer 1

Use MessageBox instead of print.

def onKeyUp(self, keycode, shift):
    pythonaddins.MessageBox("Process Started", "Process")
    pythonaddins.MessageBox("Key pressed: " + keycode, "Key")
    ....