Python: List Index out of Range Reading from File

Question

I'm using python 2.5 (I know it's an old version) and I keep getting a very frustrating 'List index out of range' exception. I'm working on a tile based game, and bellow is the code for creating the map I'm having issues with:

#Creates the list
def setMapSize(self):
    l = raw_input('Custom Map length: ')
    h = raw_input('Custom Map height: ')
    if not(l=='')and not(h==''):
        self.length = int(l)
        self.height = int(h)
        self.tileMap = [[i]*self.length for i in xrange(self.height)]
        print self.tileMap

#Load each element of the list from a text file
def loadMap(self,filePath='template.txt'):
    loadPath = raw_input('Load the map: ')
    if loadPath =='':
        self.directory = 'c:/Python25/PYGAME/TileRpg/Maps/' + filePath
        print 'Loading map from ',self.directory
        readFile = open(self.directory,'r')

        for y in xrange(self.height):
            for x in xrange(self.length):
                #reads only 1 byte (1 char)
                print '---Location: ',x,y
                print self.tileMap
                self.tileMap[x][y]=int(readFile.read(1))

        print 'Loaded map:',self.tileMap
        readFile.close()
        print 'Map loaded\n'

Here is the output and error message I get, please tell me if you know what's going on:

Main began

Map began initialization
Map initialized

Custom Map length: 2
Custom Map height: 5
[[0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]
Load the map: 
Loading map from  c:/Python25/PYGAME/TileRpg/Maps/template.txt
---Location:  0 0
[[0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]
---Location:  1 0
[[9, 0], [0, 0], [0, 0], [0, 0], [0, 0]]
---Location:  0 1
[[9, 0], [9, 0], [0, 0], [0, 0], [0, 0]]
---Location:  1 1
[[9, 9], [9, 0], [0, 0], [0, 0], [0, 0]]
---Location:  0 2
[[9, 9], [9, 9], [0, 0], [0, 0], [0, 0]]
Traceback (most recent call last):
  File "C:\Python25\PYGAME\TileRpg\LevelEditorMain.py", line 7, in <module>
    class Main():
  File "C:\Python25\PYGAME\TileRpg\LevelEditorMain.py", line 17, in Main
    tileMap.loadMap()
  File "C:\Python25\PYGAME\TileRpg\Map.py", line 48, in loadMap
    self.tileMap[x][y]=int(readFile.read(1))
IndexError: list assignment index out of range

As you can see, the index I'm assigning to seems to exist, but I still get this error.

I know that, I had to put it in the title since someone already had the title I was going to use. What's giving the exception is that it says the index is out of range. — user3050810
– user3050810, Commented Jun 30, 2014 at 11:41

Martijn Pieters · Accepted Answer · 2014-06-30 12:02:35Z

2

You swapped height and width; the outer list is of length height, not the inner. self.tileMap[0] is a list of length 2, so the maximum index you can use on it is 1, not 2.

Swapping x and y would solve this:

for x in xrange(self.height):
    for y in xrange(self.length):
        #reads only 1 byte (1 char)
        print '---Location: ',x,y
        print self.tileMap
        self.tileMap[x][y]=int(readFile.read(1))

Not that you need to use indices here, you can alter the lists directly:

for row in self.tileMap:
    row[:] = [readFile.read(1) for _ in row]

You can read a row at a time:

for row in self.tileMap:
    row[:] = map(int, readFile.read(self.length))

edited Jun 30, 2014 at 12:02

answered Jun 30, 2014 at 11:40

Martijn Pieters

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3 Comments

user3050810 Over a year ago

Swapping height and length doesn't solve the problem though, I still get an error.

Martijn Pieters Over a year ago

@user3050810: note that x is now a loop over range(self.height), not self.length.

user3050810 Over a year ago

Thanks, once I looked at your answer I worked out the problem on paper and realized my mistake.

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