Unknown error in python

Question

I am getting a strange incorrect indentation error that I cannot track down. As far as I know, I did not modify this file since last time it was correctly working.

Edit: Ok it turns out I did modify it unknowingly (obviously something had to have changed since last time). I hit a hotkey in my editor which had turned some tabs into spaces. Thanks!

The error is on line 100: ctrl f for "###"

#!/usr/bin/env python
import sys
from collections import deque #high performance queue "deck"

class Node(object):
        def __init__(self,x,y,history):
                self.locationx = x
                self.locationy = y
                self.data = None
                self.history = history #previous node to go backwards

def printNodePathTrace(inNode,width,height,mapTerrain,frontier):
    #travel backward through node history until history == None is reached
    #print off map of path
    mapPath = mapTerrain
    for i in range(width): #fill map with blanks
        for j in range(height):
            mapPath[i][j] = '-'

    #print frontier list
    print "length of frontier"
    print len(frontier)
    for item in frontier:

        #print item.locationy
        #print item.locationx
        mapPath[item.locationy][item.locationx] = '*'

    #print path found
    done = 0
    count = 0
    currentNode = inNode
    while(done == 0 and count < 50):
        mapPath[currentNode.locationy][currentNode.locationx] = '#'
        if currentNode.history == None:
            done = 1
        currentNode = currentNode.history
        count += 1
    printMap(mapPath)

def printMap(mapTerrain): #horizontal right positive x, verticle down positive y
        for i in mapTerrain:
            for j in i:
                sys.stdout.write(j)
            sys.stdout.write('\n')

def printMapStartAndGoal(mapTerrain,startX,startY,goalX,goalY):
    #Y is row, X is column. Y is vertical, X is horizontal
    temp1 = mapTerrain[startY][startX]
    temp2 = mapTerrain[goalY][goalX]
    mapTerrain[startY][startX] = 'S'
    mapTerrain[goalY][goalX] = 'G'
    printMap(mapTerrain)
    mapTerrain[startY][startX] = temp1
    mapTerrain[goalY][goalX] = temp2

def main():
    #Input map
    #Your program should be able to read a map file in the following format.
    #Width Height
    #StartX StartY
    #GoalX GoalY
    #map
    searchMode = "BFS" #options are BFS, LC, ID, A*1, A*2

    logfile = open("smallmap2.txt", "r")
    [width,height] = map(int,logfile.readline().split())
    [startX,startY] = map(int,logfile.readline().split())
    [goalX,goalY] = map(int,logfile.readline().split())

    mapTerrainInput = logfile.read()
    mapTerrain = map(list,mapTerrainInput.splitlines())
    #map the list function to mapTerrainInput split into lines without '\n'

    printMapStartAndGoal(mapTerrain,startX,startY,goalX,goalY)

    print mapTerrain
    printMap(mapTerrain)

    closedList = [] #contains list of nodes visited already
    frontier = deque([])
    startNode = Node(startX,startY,None)

    #check if node is a goal node
    #add node to closed list
    #add expansions to frontier list (not ones on closed list)
    #Repeat with next node in Frontier

    goalFound = 0 ### there's an error with this line's indentation???
    iterationCount = 0
    currentNode = startNode
    while goalFound == 0 and iterationCount < 500: #stop when goal is found
            if (currentNode.locationx == goalX and currentNode.locationy == goalY):
                    goalFound = 1
                    break

            closedList.append(currentNode)
            #expand node - currently not checking the closed list
            if (currentNode.locationy > 0): #can expand up
                frontier.append(Node(currentNode.locationx,currentNode.locationy - 1,currentNode))
            if (currentNode.locationy < height - 1): #can expand down
                frontier.append(Node(currentNode.locationx,currentNode.locationy + 1,currentNode))
            if (currentNode.locationx > 0): #can expand left
                frontier.append(Node(currentNode.locationx - 1,currentNode.locationy,currentNode))
            if (currentNode.locationx < width -1): #can expand right
                frontier.append(Node(currentNode.locationx + 1,currentNode.locationy,currentNode))
            #done expanding

            currentNode = frontier.popleft()
            iterationCount += 1


    print currentNode.history
    print currentNode.locationx
    print currentNode.locationy

    printNodePathTrace(currentNode,width,height,mapTerrain,closedList)


if __name__ == '__main__':
    main()

Answer 1

I copied and pasted your code from StackOverflow and it does not have the error. ideone

Usually this error is caused by mixing of tabs and spaces. Looking at the source for your code I see the problem. Here's how your code looks in Visual Studio with whitespace visible:

Solution

Convert the tabs to spaces.

• If your editor has an option to convert tabs to spaces, use that and you will see the problem.
• If your editor allows you to change the tab width to 8, do so and you will see the problem.
• If your editor has an option to make whitespace characters visible, try turning it on.
• Otherwise try deleting all the leading whitespace in all lines near the error and adding the spaces again (using the space key, just to be sure).
• Or just copy your code from StackOverflow back into your file and save it, since StackOverflow seems to have fixed it for you.

Answer 2

As other answers have mentioned, your issue is that you are mixing tabs and spaces, here is some proof:

I took this screenshot while "editing" your answer, and then searched for four spaces. All occurrences of four spaces are highlighted in yellow.

Note that the spacing immediately before goalFound = 0 is highlighted, but previous lines have non-highlighted spacing (indicating that tabs were used).

You should never mix tabs and spaces in your indentation because it can be hard to catch errors like this. Python treats tabs as eight spaces, but depending on your editor tabs may look equivalent to 4 spaces (or some other number). So even though your code looks like it is correctly indented, what Python actually sees looks like this:

def main():
        #... all previous lines used tabs
        #Repeat with next node in Frontier

    goalFound = 0

Answer 3

4 is the number of spaces we will use to indent. 3 is too few, 5 is too many. 8 is right out! Although, really old code that uses 8 is OK.

http://www.python.org/dev/peps/pep-0008/

Answer 4

Do you have:

1. extraneous whitespace on the blank line before the marked line
2. extraneous whitespace on the blank line after "startNode = Node(..."
3. a mixture of tabs and spaces before "goalFound = 0"?

Answer 5

You are most likely mixing tabulations and spaces. Choose one type and stick with it.