Python - Tkinter - Fifteen

# -*- coding: utf-8 -*-
# Dora Jambor, dorajambor@gmail.com
# January, 2016
# Implementation of the game fifteen in Python

# import time, pdb # you don't use it in code

from Tkinter import *

# ---------- parameters ----------
# Dimensions
min_dim = 3
max_dim = 9

# Location of blank space
blankx = 0
blanky = 0

# ---------- functions ----------
def greet():
    print 'This is the Game of Fifteen!'

def dim():
    result = int(raw_input('Insert the dimension of the board: '))
    while True:
        if result >=min_dim and result <= max_dim:
            break
        result = int(raw_input('Try again: '))
    return result


# Play the game
'''
A function called by Tkinter that allows the user to interact with the game board
and play the game by moving the tiles.
'''
def play(i,j):
    global blankx, blanky, game_running

    print 'play i,j:', i, j
    print 'blankx, blanky:', blankx, blanky

    if game_running:

        if (blankx, blanky) in [(i+1,j),(i-1,j),(i,j+1),(i,j-1)]:
            board[blanky][blankx].set(board[j][i].get())
            board[j][i].set(' ')
            blanky = j
            blankx = i

            if won():
                # lable is now visible
                bn.lift()
                game_running = False


def won():
    number = 0

    for j, row in enumerate(board):
        for i, char in enumerate(row,1):
            number += 1
            if number == d * d and char.get() == ' ':
                return True
            elif char.get() != str(number):
                return False
    return True


# Initialize the board
'''
This sets up/resets all data and variables - and fills and updates board with numbers.
'''
def setup():
    global blankx, blanky, game_running

    # set blank coordinates
    blankx = d - 1
    blanky = d - 1

    # this is where bn is marked as not defined - "global name 'bn' is not defined"
    bn.lower()

    # fill/update board with numbers
    numbers = d * d

    for row in board:
        for tile in row:
            numbers -= 1
            if numbers == 0:
                tile.set('')
            else:
                tile.set(str(numbers))

    # (re)start game
    game_running = True

# ---------- main ----------

greet()
d = dim()

board = []
# buttons = [] # you don't need it any more
# setup() # can't use before `bn = Button()`

# create window
root = Tk()
root.config(bg = 'black', borderwidth=4)
root.wm_title("Game of Fifteen")

# label for winning
bn = Button(root, text="You won!\n <click to start>", command=setup)
bn.grid(row=0, column=0, ipadx=3, ipady=10)

# frame for the board game
frame = Frame(root)
frame.config(bg='black')
frame.grid(row=0, column=0)

# fill board with StringVars
for i in range(d):
    row = []
    for j in range(d):
        var_text = StringVar()
        row.append(var_text)
    board.append(row)

setup()

for j, row in enumerate(board):
    for i, string_var in enumerate(row):
        b = Label(frame, textvariable=string_var, bg='pink', font=("Helvetica", 30), relief=RAISED)
        b.grid(row=j, column=i, sticky="nsew", ipadx=8, padx=4, pady=4)
        b.bind('<Button-1>',lambda e, i=i,j=j:play(i,j))

# game_running = True # you don't need it - `setup()` do it for you

root.mainloop()    # start engine