How do you index a list in a txt file and call on the indexed values?

Question

I am attempting to index my list, and then call on the last two values in each list separately.
For example

['Ashe', '1853282.679', '1673876.66', '1 ', '2 \n']
['Alleghany', '1963178.059', '1695301.229', '0 ', '1 \n']
['Surry', '2092564.258', '1666785.835', '5 ', '6 \n']`

I want my code to return (1, 2) #from the first list (0, 1) #from the second list (5, 6) #from the third list

my code so far includes:

def calculateZscore(inFileName, outFileName):
    inputFile = open(inFileName, "r")
    txtfile = open(outFileName, 'w')

    for line in inputFile:
        newList = (line.split(','))

    print newList

    inputFile.close()
    txtfile.close()


if __name__ == "__main__":
    main()

(I have been making attempts at indexing but the fact that there is a string in my list has been making it difficult)

i receive an error message about invalid literals – A_Worthy Dec 16 '16 at 23:23 — A_Worthy, Dec 16 '16 at 23:23

score 1 · Accepted Answer · answered Dec 16 '16 at 23:37

First, don’t put quotes around your program code. Second, here are some quick pointers:

def calculateZscore(inFileName, outFileName):
    # use with to open files to avoid having to `close` files
    # explicitly
    # inputFile = open(inFileName,"r")  
    # txtfile = open(outFileName, 'w')

    with open(inFileName, 'r') as inputFile, open(outFileName, 'w') as txtFile:
        for line in inputFile:
            newList = line.strip().split(',')
            last_two = newList[-2:] # this gets the last two items in the list  
            print last_two 



# indentation matters in python, make sure this line is indented all the way to the left, otherwise python will think it is part of 
# a different function and not the main block of running code
if __name__ == "__main__":
    main()

As an aside, it looks like you are reading CSV file. python has built-in CSV processing that you may want to consider:

def calculateZscore(inFileName, outFileName):
    import csv
    with open(inFileName, 'r') as inputFile, open(outFileName, 'w') as txtFile:
        reader = csv.reader(inputFile)
        for newList in reader:
            last_two = newList[-2:] # this gets the last two items in the list  
            print last_two

Thanks so much. That definitely works. You are correct it is a csv file but i was told to treat it as a txt file (idk why). I was unaware that you could preform .split() & .strip() at the same time. Also I'm guessing [-2:] preserves the last two characters in the list? That's super helpful to know for the future. — A_Worthy, Dec 16 '16 at 23:58
It preserves the last two elements in the list. So `['apple', 'banana', 'cookie', 'donut'][-2:] == [ 'cookie', 'donut']`, — 2ps, Dec 17 '16 at 00:00
I have a side question.....Is there a way to call the last two value without deleting/removing the rest of the list?.....or is that what I am already doing? — A_Worthy, Dec 17 '16 at 00:08
@A_Worthy you are already doing it if you use the answer. The "old" list is newList which contains all elements in a line and the "new" list containing only the last two elements is last_two. — fedepad, Dec 17 '16 at 00:25

score 0 · Answer 2 · answered Dec 16 '16 at 23:35

0

Use

newList = line.rstrip('\n').split(',')[-2:]

but this line should be intended with respect to the for loop, not as you show in your code example.

answered Dec 16 '16 at 23:35

fedepad

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How do you index a list in a txt file and call on the indexed values?

2 Answers2