TypeError: 'NoneType' object does not support item assignment?

Question

So I start a root screen with a "file select" and a "go" button. The go button is disabled and I want to make it active after the file has been selected. When I select the file go should become active but instead this error "TypeError: 'NoneType' object does not support item assignment" Here is some sample code

import Tkinter
import tkFileDialog

def chooseDir():
    dir1=tkFileDialog.askopenfilename(parent=root, title='choose file path')
    go['state']=Tkinter.ACTIVE
root=Tkinter.Tk()
global go
go=Tkinter.Button(text='file location',command=chooseDir,state=Tkinter.DISABLED).pack()
root.mainloop()

Answer 1

This line:

go=Tkinter.Button(text='file location',command=chooseDir,state=Tkinter.DISABLED).pack()

is creating a temporary object, then calling pack() on it. The pack method returns None, so go is assigned None.

Remove the .pack() then go will be the Button object. Then call go.pack().