python parsing csv file

Question

I am parsing a csv file where the first line is the header. I want to sum the amount column according to dates, but am getting an error message. To debug I am checking if the column is a digit as well as if it is a string according to the error message - and it is both. What could be the reason for this?

def parseDataFromFile(self,f):
    fh = open(f,'r')
    s = 0
    for line in fh:
        #parsing the line according to comma and stripping the '\n' char
        year,month,day,amount = line.strip('\n').split(',')

        #checking the header row, could check if was first row as well - would be faster
        if (amount == "Amount"): continue

        #just for the debug checks
        #here is the question

        if isinstance(amount,str):
            print "amount is a string"
            #continue
        if amount.isdigit:
            print "amount is a digit"

        #sum on the amount column
        s = s + amount

Output: amount is a string amount is a digit amount is a string amount is a digit

Error:

s = s + amount 
TypeError: unsupported operand type(s) for +: 'int' and 'str'

Ned Batchelder · Accepted Answer · 2012-07-17 14:21:08Z

5

Your problem is that s is an integer, you initialize it to 0. Then you try to add a string to it. amount is always a string. You do nothing to turn your number-like data into actual numbers, it will always be a string.

If you expect amount to be a number, then use:

s += float(amount)

PS: you should use the csv module in the stdlib for reading CSV files.

answered Jul 17, 2012 at 14:21

Ned Batchelder

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Comments

Tim Pietzcker · Accepted Answer · 2012-07-17 14:21:42Z

1

if amount.isdigit:
    print "amount is a digit"

will always print "amount is a digit" because you're not calling the method (it should be if amount.isdigit():).

You can be sure that any field you get by splitting a line from a CSV file will be a string, you'll need to convert it to an int first:

s = s + int(amount)

answered Jul 17, 2012 at 14:21

Tim Pietzcker

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Jon Clements · Accepted Answer · 2012-07-17 14:48:54Z

0

Something like?: (assuming column headers are "Year", "Month", "Day", "Amount")

from collections import defaultdict
import csv

sum_by_ym = defaultdict(float)
with open('input_file.csv') as f:
    for row in csv.DictReader(f):
        sum_by_ym[(row['Year'], row['Month'])] += int(float['Amount'])

print sum_by_ym

edited Jul 17, 2012 at 14:48

answered Jul 17, 2012 at 14:34

Jon Clements

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Comments

octopusgrabbus · Accepted Answer · 2012-07-17 19:29:07Z

0

s is an int, and amount is a string representation of a number, so change s = s + amount to s += int(amount)

edited Jul 17, 2012 at 19:29

octopusgrabbus

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answered Jul 17, 2012 at 14:21

Tyler Crompton

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