Python: IndexError: list index out of range Error

Question

Updated, look bottom!

I am stuck! I get a IndexError: list index out of range Error.

def makeInverseIndex(strlist):
    numStrList = list(enumerate(strlist))
    n = 0 
    m = 0 
    dictionary = {}
    while (n < len(strList)-1):
        while (m < len(strlist)-1):
            if numStrList[n][1].split()[m] not in dictionary:
                dictionary[numStrList[n][1].split()[m]] = {numStrList[n][0]}
                m = m+1
            elif {numStrList[n][0]} not in dictionary[numStrList[n][1].split()[m]]:
                dictionary[numStrList[n][1].split()[m]]|{numStrList[n][0]} 
                m = m+1
        n = n+1                
return dictionary

it gives me this error

>>> makeInverseIndex(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "./inverse_index_lab.py", line 23, in makeInverseIndex
    if numStrList[n][1].split()[m] not in dictionary: 
IndexError: list index out of range

I don't get it... what causes this? It happens even when I change the conditions of the while loop. I don't get what is the problem. I am pretty new at this, so explain it like you would if a piece of broccoli asked you this question.

Edit:

Thanks guys, I forgot to mention examples of input, I want to input something like this:

 L=['A B C', 'B C E', 'A E', 'C D A']

and get this as output:

D={'A':{0,2,3}, 'B':{0,1}, 'C':{0,3}, 'D':{3}, 'E':{1,2}}

so to create a dictionary that shows where in the list you might find a 'A' for example. It should work with a huge list. Do anyone have any tips? I want it to iterate and pick out each letter and then assign them a dictionary value.

Edit number two:

Thanks to great help from you guys my code looks beautiful like this:

def makeInverseIndex(strList):
numStrList = list(enumerate(strList))
n = 0
dictionary = {}
while (n < len(strList)):
    for word in numStrList[n][1].split():
        if word not in dictionary:
            dictionary[word] = {numStrList[n][0]}
        elif {numStrList[n][0]} not in dictionary[word]:
            dictionary[word]|={numStrList[n][0]} 
    n = n+1                     

return dictionary

But I still manage to get this error when I try to run the module:

   >>> makeInverseIndex(L)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "./inverse_index_lab.py", line 21, in makeInverseIndex
    for word in numStrList[n][1].split():
NameError: global name 'StrList' is not defined

I do not see where the error can come from.

Answer 1

Good to see some smart veggies programming.

First, your question. Like @Vasiliy said, you have 3 indices. The n is alright, since you protect it with your while condition. The 1 is fine since enumerate always generates 2 things. That just leaves m . This is your problem.

Let's say you have N elements in strlist . For each element e in strlist , you apply split() to it. The number of elements in e.split() is not always equal to N . The while condition for m guards against N , not against len(e.split()) , hence the index out of range.

To solve this, split the string first, and then loop through it. While you're at it, might as well get rid of m altogether, splitting the string only once, and gain some performance. Plus, you never reset your m , which just grows and grows.

while (n < len(strList)):
    for word in numStrList[n][1].split():
        if word not in dictionary:
            dictionary[word] = {numStrList[n][0]}
        elif {numStrList[n][0]} not in dictionary[word]:
            dictionary[word]|={numStrList[n][0]} 
    n = n+1         

Second, your while conditions are too restrictive. n < len(strlist) is fine.

Answer 2

I do not have enough reputation to leave a comment on your post so I'm posting an answer here:

I have copy and pasted the latest code at the bottom (edit 2) and it runs as expected, so there are two potential issues I can see:

1) You might have forgotten to indent your function definition 2) You might have capitalized strList to StrList in your function definition and then declared StrList elsewhere.

Hope this helps.

Answer 3

You can always do something like this as well if you want to guard against this error.

try:
    #The code that causes the issue
except IndexError:
    pass