What am I doing wrong? I want the 'refreshB' button to call the 'update' def but I get a nameError instead

```
class monitor():
    def update(self):
        print "Called"

    mon = Tk()
    mainFrame = Frame(mon)
    mainFrame.grid(row=1, column=1)

    optionFrame = Frame(mainFrame)
    optionFrame.grid(row=1, column=1)

    refreshB = ttk.Button(optionFrame, text='Refresh', command=lambda: update('self') )
    refreshB.grid(row=1, column=1)

    mon.mainloop()

monitor()

**NameError: global name 'update' is not defined**

```

I an not very familiar with Classes, is there something else I am supposed to add?

If the script above was not a class then I would use:

```
refreshB = ttk.Button(optionFrame, text='Refresh', command=lambda: update )

```

Which would works fine...