Code supplementing the Using the Python "heapq" Module and Priority Queues article.

Run the following program:

$ python shortest-path.py

It will print out a map with the shortest path from the top-left corner to the bottom-right corner indicated with @.

In order to change the map the robot uses, modify the triple-quoted string that is assigned to map near the top of the file. Anything except X is interpreted as free from obstacles. Using . makes the map easier to read directly. You can make the map bigger, and a lot more complicated.

If there are so many obstacles that make finding a path from the top-left corner to the bottom right corner impossible, the program will raise an exception.

If you want to play around with the code, here are some changes that you can make:

• How would you change the code so that the robot cannot go diagonally?
• How would you change the code so that the robot can only move right or down, but never left or up?
• (Harder) How would you change the code so that every step consumes energy, squares with * give energy, and the robot cannot move if it is out of energy?
• (Challenge) How would you change the code so that areas marked with # are not obstacles, but take twice as long to move through?