Tkinter button 'not defined' when ran - python-2.7

Question

I am following a quick guide online to start using Tk in Python (2.7) and so far, I have this code:
from Tkinter import *
root = Tk()
root.title("Note Taker")
root.mainloop()
button1 = Button(root, text="button1", command = Button1)
button2 = Button(root, text="button2", command = Button2)
button3 = Button(root, text="button3", command = Button3)
text = Entry(root)
listbox = Listbox(root)
text.pack()
button1.pack()
button2.pack()
button3.pack()
listbox.pack()
def Button1():
listbox.insert(END, "button1 pressed")
def Button2():
listbox.insert(END, "button2 pressed")
def Button3():
text_contents = text.get()
listbox.insert(END, text_contents)
text.delete(0,END)
However when I run this, the GUI is loaded, however none of the buttons are shown, instead I am given this 'NameError':
button1 = Button(root, text="button1", command = Button1)
NameError: name 'Button1' is not defined
I'm sure its purely my error however what could be changed to make this run correctly?

Answer 1

Move
def Button1():
listbox.insert(END, "button1 pressed")
before
button1 = Button(root, text="button1", command=Button1)
since command = Button1 references Button1.
And of course, do the same for Button2 and Button3.
Also move
root.mainloop()
to the bottom of the script, so the flow of control does not get caught in the event loop before the Tkinter widgets are defined.
from Tkinter import *
root = Tk()
root.title("Note Taker")
def Button1():
listbox.insert(END, "button1 pressed")
def Button2():
listbox.insert(END, "button2 pressed")
def Button3():
text_contents = text.get()
listbox.insert(END, text_contents)
text.delete(0, END)
button1 = Button(root, text="button1", command=Button1)
button2 = Button(root, text="button2", command=Button2)
button3 = Button(root, text="button3", command=Button3)
text = Entry(root)
listbox = Listbox(root)
text.pack()
button1.pack()
button2.pack()
button3.pack()
listbox.pack()
root.mainloop()