a-star.py

"""
NOT MY CODE! 
Sourced and adapted from https://medium.com/@nicholas.w.swift/easy-a-star-pathfinding-7e6689c7f7b2.
All credits go to the respective owners.

I used this as a base for early investigations into A*'s performance.
Some of my own code and functions have been appended in order to allow compatibility.
This can be tested and run as normal.
"""
class Node():
    """A node class for A* Pathfinding"""

    def __init__(self, parent=None, position=None):
        self.parent = parent
        self.position = position

        self.g = 0
        self.h = 0
        self.f = 0

    def __eq__(self, other):
        return self.position == other.position


def astar(maze, start, end):
    """Returns a list of tuples as a path from the given start to the given end in the given maze"""

    # Create start and end node
    start_node = Node(None, start)
    start_node.g = start_node.h = start_node.f = 0
    end_node = Node(None, end)
    end_node.g = end_node.h = end_node.f = 0

    # Initialize both open and closed list
    open_list = []
    closed_list = []

    # Add the start node
    open_list.append(start_node)

    # Loop until you find the end
    while len(open_list) > 0:

        # Get the current node
        current_node = open_list[0]
        current_index = 0
        for index, item in enumerate(open_list):
            if item.f < current_node.f:
                current_node = item
                current_index = index

        # Pop current off open list, add to closed list
        open_list.pop(current_index)
        closed_list.append(current_node)

        # Found the goal
        if current_node == end_node:
            path = []
            current = current_node
            while current is not None:
                path.append(current.position)
                current = current.parent
            return path[::-1] # Return reversed path

        # Generate children
        children = []
        for new_position in [(0, -1), (0, 1), (-1, 0), (1, 0), (-1, -1), (-1, 1), (1, -1), (1, 1)]: # Adjacent squares

            # Get node position
            node_position = (current_node.position[0] + new_position[0], current_node.position[1] + new_position[1])

            # Make sure within range
            if node_position[0] > (len(maze) - 1) or node_position[0] < 0 or node_position[1] > (len(maze[len(maze)-1]) -1) or node_position[1] < 0:
                continue

            # Make sure walkable terrain
            if maze[node_position[0]][node_position[1]] != "-":
                continue

            # Create new node
            new_node = Node(current_node, node_position)

            # Append
            children.append(new_node)

        # Loop through children
        for child in children:

            # Child is on the closed list
            for closed_child in closed_list:
                if child == closed_child:
                    continue

            # Create the f, g, and h values
            child.g = current_node.g + 1
            child.h = ((child.position[0] - end_node.position[0]) ** 2) + ((child.position[1] - end_node.position[1]) ** 2)
            child.f = child.g + child.h

            # Child is already in the open list
            for open_node in open_list:
                if child == open_node and child.g > open_node.g:
                    continue

            # Add the child to the open list
            open_list.append(child)

"""
My code below...
"""

def get_file(filename):
    f = open(filename)
    maze = []
    for x in f:
        maze.append(x.split())
    return maze
    
    
def check_grid(grid):
    w = len(grid[0])
    for row in grid:
        if len(row) != w:
            raise Exception("Erroneous maze supplied.")
    return;

def check_entrance_exit(grid):
    h = len(grid)
    try:
        if ((grid[0].count("#")) != len(grid[0]) - 1) or ((grid[h-1].count("#")) != len(grid[0]) - 1):
            raise Exception("Erroneous maze supplied.")
        return ((0, grid[0].index("-")), (h-1, grid[h-1].index("-")))
    except ValueError:
        raise Exception("Erroneous maze supplied.")


def main():
    maze = get_file("maze-Medium.txt")
    targets = check_entrance_exit(maze)
    path = astar(maze, targets[0], targets[1])
    print(path)


if __name__ == '__main__':
    main()