CODEWITHSUNDEEP
pythoncsv
Martin Pugsley
Martin Pugsley

Reputation: 31

Finding a cell in a csv file?

How would I go about writing to a CSV file in Python?

I basically have 2 columns. First column is a list of transaction names, the 2nd column is timings.

I need to create a piece of code that can update the timings column when a user fills in an entry box.

I have setup the entrybox in tkinter and have setup the text variable ready. I'm ok with getting the variable but the problem I am having is taking the textvariable and finding the correct cell in the csv file and overwriting it.

Essentially I want to find the correct cell and paste the value over whats in the csv file.

any ideas?

thanks

Upvotes: 0

Views: 1008

Answers (2)

supernun
supernun

Reputation: 491

Assuming you have a file called file.csv that looks like this:

Col1,Col2
entry1,timestamp1
entry2,timestamp2

You can use the csv library like this to modify any entry and paste it in a new .csv.new file (you can choose to remove the '.new' extension but it will overwrite your old file):

import csv
csv_file = "file.csv"

file_dict = {}
with open(csv_file, mode='rb') as f:
    reader = csv.reader(f)
    top_row = next(reader)
    for row in reader:
        file_dict[row[0]] = row[1]

# get transaction name and timing
transaction_name = "entry1"
timing = "timestamp3"

# do the update
file_dict[transaction_name] = timing

# create updated version of file
with open(csv_file+".new", mode='wb') as out_f:
    writer = csv.writer(out_f)
    writer.writerow(top_row)
    writer.writerows(file_dict.items())

Note this will likely rearrange your csv file. You didn't specify if this was a concern or not. If it is you can sort the dict or use an OrderedDict. See here for more info: https://docs.python.org/2/library/collections.html#collections.OrderedDict

Upvotes: 1

galimay
galimay

Reputation: 415

You can create a temporal file, copy the lines to the tmp file, and then replace only the line that starts with the transaction name. Assuming a CSV with the tuple [name, value] per line, you can use something like this:

from tempfile import mkstemp
from os import close
from shutil import move

def update(filename, name, value):
    fd, path = mkstemp()
    with open(path,'w') as tmpfile:
        with open(filename) as csv:
            for line in cvs:
                if line.startswith(name):
                    tmpfile.write(",".join([name,value]))
                else:
                    tmpfile.write(line)
    close(fd)
    move(path, filename)

Upvotes: 2

Related Questions