CODEWITHSUNDEEP
pythonpython-3.xlist
Samuel Kusenuh
Samuel Kusenuh

Reputation: 11

IndexError: list index out of range. (trying to find and substitute elements of one txt file with another txt file

beginning python programmer here. I am currently stuck with writing a small python script that would open a txt source file, find a specific number in that source file with a regular expression (107.5 in this case) and ultimately replace that 107.5 with a new number. the new number comes from a second txt file which contains 30 numbers. Each time a number has been replaced, the script uses the next number for its replacement. Although the command prompt does seem to print a successfull find and replace, "an IndexError: list index out of range" occurs after the 30th loop...

My hunge is that I somehow have to limit my loop with something like "for i in range x". However I am not sure which list this should be and how I can incorporate that loop limitation in my current code. Any help is much appreciated! 

nTemplate = [" "]

output = open(r'C:\Users\Sammy\Downloads\output.txt','rw+')

count = 0

for line in templateImport:
   priceValue = re.compile(r'107.5')

   if priceValue.sub(pllines[count], line) != None:
      priceValue.sub(pllines[count], line)
      nTemplate.append(line)
      count = count + 1
      print('found a match. replaced ' + '107.5 ' + 'with ' + pllines[count] )
      print(nTemplate)

   else:
      nTemplate.append(line)

Upvotes: 1

Views: 90

Answers (1)

shriakhilc
shriakhilc

Reputation: 3000

The IndexError is raised because you are incrementing count in each iteration of the loop, but haven't added an upper limit based on how many values the pllines list actually contains. You should break out of the loop when it reaches len(pllines) in order to avoid the error.

Another issue which you may not have noticed is with your usage of the re.sub() method. It returns a new string with the appropriate replacements, and does not modify the original.

If the pattern doesn't exist in the string, it'll return the original itself. So your nTemplate list probably never had any of the replaced strings appended to it. Unless you need to do some other actions if the pattern was found in the line, you can do away with the if condition (as I have in the example below).

Since the priceValue object is the same for all lines, it can be moved outside the loop.

The following code should work:

nTemplate = [" "]
output = open(r'C:\Users\Sammy\Downloads\output.txt','rw+')

count = 0
priceValue = re.compile(r'107.5')

for line in templateImport:
    if count == len(pllines):
        break
    nTemplate.append(priceValue.sub(pllines[count], line))
    count = count + 1
    print(nTemplate)

Upvotes: 0

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