Python 2.7.1: How to Open, Edit and Close a CSV file

Question

I\'m having trouble opening a file (amount2.csv) making a change, saving it and closing the file.

How does one open a file edit, save and close it?

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Answer 1

The

<open file 'amount2.csv', mode 'r' at 0x1004656f0>

you are seeing isn't an error, but the result of your 'print f'. To instead see the contents of your file, you would do

with open('test.csv', 'rb') as f:
    reader = csv.reader(f)
    for row in reader:
        # row is a list of strings
        # use string.join to put them together
        print ', '.join(row)

To append rows to your file, instead do

changes = [    
    ['1 dozen','12'],                                                            
    ['1 banana','13'],                                                           
    ['1 dollar','elephant','heffalump'],                                         
    ]                                                                            

with open('test.csv', 'ab') as f:                                    
    writer = csv.writer(f)                                                       
    writer.writerows(changes)

More info at Python CSV Docs

EDIT:

I misunderstood at first, you want to change all entries of '1 dozen' to '12' in your csv file. I will say first, this is easier to do without using the csv module, but here is a solution using it.

import csv

new_rows = [] # a holder for our modified rows when we make them
changes = {   # a dictionary of changes to make, find 'key' substitue with 'value'
    '1 dozen' : '12', # I assume both 'key' and 'value' are strings
    }

with open('test.csv', 'rb') as f:
    reader = csv.reader(f) # pass the file to our csv reader
    for row in reader:     # iterate over the rows in the file
        new_row = row      # at first, just copy the row
        for key, value in changes.items(): # iterate over 'changes' dictionary
            new_row = [ x.replace(key, value) for x in new_row ] # make the substitutions
        new_rows.append(new_row) # add the modified rows

with open('test.csv', 'wb') as f:
    # Overwrite the old file with the modified rows
    writer = csv.writer(f)
    writer.writerows(new_rows)

If you're new to programming and python the most trobulesome line is probably

new_row = [ x.replace(key, value) for x in new_row ]

but this is just a list comprehension that is effectively equivalent to

temp = []
for x in new_row:
    temp.append( x.replace(key, value) )
new_row = temp

Answer 2

You're trying to print the file object itself, which won't do much useful. Have you looked at the documentation for the CSV module? The very first code example shows you how to use csv.reader.