Algorithm for knight’s tour in Python

• One of the interesting puzzlers for chess buffs is the Knight's Tour problem, originally proposed by the mathematician Euler. The question is: Can the chess piece called the knight move around an empty chessboard and touch each of the 64 squares once and only once?

• To solve, this program uses Warnsdorf's rule http://en.wikipedia.org/wiki/Knight%27s_tour

• Each potential move will be tested to make sure it doesn't land off the board and doesn't revisit the old move.

• This program will use accessibility heuristic. Accessibility of a square will be equal precisely to the number of squares from which that square may be reached. At any time, the knight should move to the square with the lowest accessibility.

• When encountering a tie in accessibility between two or more squares, decides what square to choose by looking ahead to those squares reachable from the "tied" squares. The program should move to the square for which the next move would arrive at a square with the lowest accessibility number.