[Tutor] how to change the command "string" on a tkinter Button?

[Chris Roy-Smith]

Hi,

OS is Linux,

Python version is 3.6.5

I am trying to change the command of a tkinter Button in my program. 
Eventually I want to be able to do this to many buttons.

My attempt at code brings up no error messages, but the button appears 
to do nothing.

I really have no idea how to do this, but this is what I wrote.

====================================

#!/usr/bin/python3
from tkinter import *

class form(object):
     def __init__(self, x, reply, master, z,bu):
         self.x=x
         self.reply=reply
         self.master=master
         self.z=z
         self.bu=bu

     def change(x, reply, z, b):
         #f contains the alternative command (as a string)
         f=["lambda x=vars, txt=reply,fu=0 bu=b1 :form.change(x, txt, 
fu, bu)", "lambda x=vars, txt=first, fu=1 bu=b1: form.change(x, txt, fu, 
bu)"]
         for i in range(4):
             x[i].set(reply[i])
         #attempt to change command clause
         set.button(f[z])

     def draw(master):
         vars = []
         label = []
         button = StringVar
         for i in range(4):
             var = StringVar()
             vars.append(var)
             label.append("")
             label[i] = Label( master, textvariable=var, relief=RAISED 
).grid(row=i, column=0)
             vars[i].set(first[i])
         b1=Button(master, text="change", command=button).grid(row=i+1, 
column=0)


reply=["now I don't know", "Happy birthday", "Many happy returns", "Next 
it's my turn",1]
first=["What's your name?", "My name is Fred", "I have just had my 
birthday", "your's is next!",2]
master=Tk()

form.draw(master)
master.mainloop()

=================================

How should I do this, I had worked around the problem by destroying  the 
window and building it again, but it was pointed out that I have an 
unusual coding style doing this.

All hints appreciated!

Regards, Chris Roy-Smith