In Python 2.7 - How To Read Data From Csv, Reformat Data, And Write To New Csv

I'm a programing noob, and I'm stuck... My goal is to open a csv file (an export from program A), reformat the data, and write it to a new csv file (for program B to import). I k

Solution 1:

You are re-opening the file and overwriting it on each pass through the for p in myCSV loop. You need to create w once before entering the for loop.

Solution 2:

The following modified code should work:

import csv

print'Enter file location or press enter for default location.'
aPath = raw_input('> ')  # user path to fileif aPath == '':
    aPath = '/default/path/to/file'# default path
aFile = raw_input('Enter file name: ')  # user file nameif aFile == '':
    aFile = 'orginal.csv'# default file name
myCSV = csv.DictReader(open(aPath + aFile, 'r'), delimiter=',')
print myCSV.fieldnames # verify fieldnameswithopen("output.csv", "wb") as ofile:
    w = csv.writer(ofile)
    for p in myCSV:
        try:
            p = dict((k, v) for k, v in p.iteritems()
                if v.lower() != 'null')
        except AttributeError, e:
            print e
            print p
            raise Exception()
    # reformats the columns of data for the output.csv
        pID = p.get('Last Name')[-4:]
        pName = p.get('Last Name')[:-4].strip() + ', ' + p.get('First Name')
        pDate = p.get('Start Time')[:-5]
        pBlank = p.get('')
        pCourse = p.get('Assigned Through')
        pScore = p.get('Score')[:-1]

    # verifies the new columnsprint pID, pName, pDate, pBlank, pCourse, pBlank, pBlank, pScore

    # NOT working...Only writes the last row of the orginal.csv to output.csv
        w.writerow([pID, pName, pDate, pBlank, pCourse, pBlank, pBlank, pScore])

Things we changed:

1. We used the with operator. When working with opening and closing files, using with is a generally accepted protocol to follow unless otherwise inapplicable since it handles the closing of files properly, among other things.
2. Use wb instead of just w as your second argument to open. This will allow you to open the file in write-binary mode. See this for reference.

Hope this helps.

Solution 3:

I'm afraid you're re-writing your output file at each iteration ... You should simply take the line

w = csv.writer(open("output.csv", "w"))

out of the loop as :

w = csv.writer(open("output.csv", "w"))
try:
    for p in myCSV:
        try:
            ...
            w.writerow([pID, pName, pDate, pBlank, pCourse, pBlank, pBlank, pScore])
finally:
    w.close()

You could also have a look to "with" constructs that automatically cope with potential io errors and close the file at end of block with no need for the additional try.