Initially, a chessboard is displayed with a single chess piece, a black knight, who may be dragged to another square. Below the board are three controls: a Start button, a Repeat checkbox and a Speed scale. Pressing Start begins the tour which is calculated using an enhanced Warnsdorff's rule (see the original tcl file for more info). As the knight begins to move around the board, the position changes are recorded in the text widget to the right of the board. Drag the scale to change the speed with which the knight is moved. Click the Repeat checkbox to run random tours continuously.
Note that the knight will disappear if dragged off the board; hit Start to have him repositioned.
# File: knightstour.py
# http://infohost.nmt.edu/tcc/help/pubs/tkinter//canvas.html
# http://www.fileformat.info/info/unicode/char/265e/index.htm
# http://opensource.apple.com/source/tcl/tcl-87/tk/tk/library/demos/knightstour.tcl
import random
from tkinter import *
from tkinter import ttk
from tkinter.font import Font
from demopanels import MsgPanel, SeeDismissPanel
class KnightsTourDemo(ttk.Frame):
def __init__(self, isapp=True, name='knightstourdemo'):
ttk.Frame.__init__(self, name=name)
self.pack(expand=Y, fill=BOTH)
self.master.title('Knights Tour Canvas Demo')
self.isapp = isapp
self._create_widgets()
def _create_widgets(self):
if self.isapp:
# message panel not required
SeeDismissPanel(self)
self._create_demo_panel()
def _create_demo_panel(self):
demoPanel = Frame(self, name='demo')
demoPanel.pack(side=TOP, fill=BOTH, expand=Y)
board = self._create_tour(demoPanel)
self._add_bindings(board)
def _create_tour(self, parent):
c = Canvas(parent, width=240, height=240, name='board')
self._draw_board(c)
txt = Text(parent, width=10, height=1, name='dlg',
background='white', font=('Arial', 8))
vscroll = ttk.Scrollbar(parent, orient=VERTICAL,
command=txt.yview)
txt['yscrollcommand'] = vscroll.set
controls = self._create_controls(parent, c)
# position and configure resize behaviour
c.grid(row=0, column=0, sticky='news')
txt.grid(row=0, column=1, sticky='news')
vscroll.grid(row=0, column=2, sticky='news')
controls.grid(row=1, column=0, columnspan=3,
sticky=N+E)
parent.rowconfigure(0, weight=1)
parent.columnconfigure(1, weight=1)
return c
def _draw_board(self, canvas):
# draw checkerboard
for r in range(7, -1, -1):
for c in range(8):
if c&1 ^ r&1:
fill = 'tan3'
dfill = 'tan4'
else:
fill = 'bisque'
dfill= 'bisque3'
coords = (c*30+4, r*30+4, c*30+30, r*30+30)
canvas.create_rectangle(coords,
fill=fill,
disabledfill=dfill,
width=2,
state='disabled')
# create knight
canvas.create_text(0, 0, font=('Courier 20'), text='\u265e',
anchor='nw', tags='knight',
fill='black', activefill='#600000')
# randomly place him on the board
self._put_random_knight(canvas)
def _create_controls(self, parent, canvas):
# board controls
delay = IntVar()
continuous = BooleanVar()
frame = ttk.Frame(parent, name='controls')
ttk.Label(frame, text='Speed').pack(side=RIGHT, padx=(4,24), pady=12)
ttk.Scale(frame, from_=8, to=2000,
variable=delay).pack(side=RIGHT, padx=4, pady=12)
ttk.Checkbutton(frame, text='Repeat',
variable=continuous).pack(side=RIGHT, padx=4, pady=12)
btn = ttk.Button(frame, text='Start', name='start')
btn['command'] = self._start_tour
btn.pack(side=RIGHT, padx=(16,4), pady=12)
# set variable values and safe a reference to them
delay.set(600)
continuous.set(False)
canvas.__delay = delay
canvas.__continuous = continuous
return frame
# ========================================================================
# Bindings
# ========================================================================
def _add_bindings(self, board):
board.tag_bind('knight', '<1>',
lambda e, b=board: self._start_drag(e, b))
board.tag_bind('knight', '<B1-Motion>',
lambda e, b=board: self._drag(e,b))
board.tag_bind('knight', '<ButtonRelease-1>',
lambda e, b=board: self._end_drag(e,b))
# ========================================================================
# Bound methods
# ========================================================================
def _start_drag(self, evt, board):
# save drag start coords
board.__lastX = board.canvasx(evt.x)
board.__lastY = board.canvasy(evt.y)
def _drag(self, evt, board):
# move the knight with the mouse
x = board.canvasx(evt.x)
y = board.canvasy(evt.y)
board.move(CURRENT, x-board.__lastX, y-board.__lastY)
board.__lastX = x
board.__lastY = y
def _end_drag(self, evt, board):
# place the knight in the square closest to
# the mouse position
square = board.find_closest(evt.x, evt.y, 0, 65)
coords = board.coords(square)
board.coords(CURRENT, (coords[0], coords[1]))
# ========================================================================
# Commands
# ========================================================================
def _start_tour(self, square=None):
# start a new Knight's Tour
self._toggle_start_btn('disabled')
b = self.nametowidget('demo.board') # board
t = self.nametowidget('demo.dlg') # text
t.delete(1.0, END) # clear text
visited = [] # squares visited in this tour
for n in range(64):
b.itemconfigure(n, {'state': 'disabled',
'outline': 'black'})
if not square:
# get start position from current placement of knight
coords = b.coords('knight')
square = b.find_closest(coords[0], coords[1], 0, 65)
if square[0] > 64:
# knight is off the board
self._put_random_knight(b)
coords = b.coords('knight')
square = b.find_closest(coords[0], coords[1], 0, 65)
square = (square[0]-1, )
b.__initial = square # save starting square
self._move_piece(b, t, square, square, visited)
# ========================================================================
# Chessboard methods
# ========================================================================
def _toggle_start_btn(self, newState):
sbtn = self.nametowidget('demo.controls.start')
sbtn.configure(state=newState)
def _put_random_knight(self, board):
# randomly choose a board square and position
# the knight
sqr = int( 1 + random.random() * 64)
coords = board.coords((sqr, ))
board.coords('knight', (coords[0], coords[1]))
def _move_piece(self, b, txt, last, square, visited):
# b - chess board (canvas)
# txt - text console
# last - last square visited
# square - current square
# display the square moves using standard
# chess nomenclature
chessSqr = '{}. {} .. {}\n'.format(len(visited),
self._chess_sqr(last),
self._chess_sqr(square) )
txt.insert(END, chessSqr )
txt.see(END)
# configure squares, move the knight and update visited squares
b.itemconfigure(1+last[0], state='normal', outline='black')
b.itemconfigure(1+square[0], state='normal', outline='red')
coords = b.coords(1+square[0])
b.coords('knight', (coords[0], coords[1]))
visited.append(square[0])
# get the next move
next = self._next_square(square[0], visited)
if next != -1:
# new legal move, pause and then move the knight
self.after(b.__delay.get(), self._move_piece, b, txt, square, (next,), visited)
else:
# no legal moves left
if len(visited) == 64:
if b.__initial == square:
txt.insert(END, 'Closed tour!\n')
self._toggle_start_btn('normal')
else:
txt.insert(END, 'Success\n')
self._toggle_start_btn('normal')
if b.__continuous.get():
self.after(b.__delay.get() * 2,
self._start_tour,
self._put_random_knight(b))
else:
txt.insert(END, 'Failed!\n')
self._toggle_start_btn('normal')
return
def _chess_sqr(self, square):
# Display a square number as a standard chess square notation.
return '{}{}'.format(chr(97 + square[0]%8), square[0]//8 + 1)
def _valid_moves(self, square):
# Return a list of squares accessible from the given square
moves = []
pairs = [(-1,-2), (-2,-1), (-2,1), (-1,2), (1,2), (2,1), (2,-1), (1,-2)]
for p in pairs :
col = (square % 8) + p[0]
row = (square // 8) + p[1]
if (-1 < row < 8) and (-1 < col < 8):
moves.append(row * 8 + col)
return moves
def _check_squares(self, square, visited):
# Return the number of available moves for this square
moves = 0
for test in self._valid_moves(square):
if test not in visited:
moves += 1
return moves
def _next_square(self, square, visited):
# Select the next square to move to.
# Returns -1 if no valid moves left
minimum = 9
nextSqr = -1
for t in self._valid_moves(square):
if t not in visited:
count = self._check_squares(t, visited)
if count < minimum:
minimum = count
nextSqr = t
elif count == minimum:
nextSqr = self._edgemost(nextSqr, t)
return nextSqr
def _edgemost(self, a, b):
# Select the square nearest the edge of the board
colA = 3 - int(abs(3.5 - (a % 8)))
colB = 3 - int(abs(3.5 - (b % 8)))
rowA = 3 - int(abs(3.5 - (a // 8)))
rowB = 3 - int(abs(3.5 - (b // 8)))
if (colA * rowA) < (colB * rowB):
return a
else:
return b
if __name__ == '__main__':
KnightsTourDemo().mainloop()