Python – Change specific value in CSV file via Python

csvpython

I need a way to change the specific value of a column of a CSV file. For example I have this CSV file:

"Ip","Sites"
"127.0.0.1",10
"127.0.0.2",23
"127.0.0.3",50

and I need to change the value 23 to 30 of the row "127.0.0.2".

I use csv library: import csv

This is the solution opening the csv file, changing the values in memory and then writing back the changes to disk.

r = csv.reader(open('/tmp/test.csv')) # Here your csv file
lines = list(r)

Content of lines:

[['Ip', 'Sites'],
 ['127.0.0.1', '10'],
 ['127.0.0.2', '23'],
 ['127.0.0.3', '50']]

Modifying the values:

lines[2][1] = '30'

Content of lines:

[['Ip', 'Sites'],
 ['127.0.0.1', '10'],
 ['127.0.0.2', '30'],
 ['127.0.0.3', '50']]

Now we only have to write it back to a file

writer = csv.writer(open('/tmp/output.csv', 'w'))
writer.writerows(lines)

Assuming module foo with method bar:

import foo
method_to_call = getattr(foo, 'bar')
result = method_to_call()

You could shorten lines 2 and 3 to:

result = getattr(foo, 'bar')()

if that makes more sense for your use case.

You can use getattr in this fashion on class instance bound methods, module-level methods, class methods... the list goes on.

shutil has many methods you can use. One of which is:

from shutil import copyfile
copyfile(src, dst)

# 2nd option
copy(src, dst)  # dst can be a folder; use copy2() to preserve timestamp

Copy the contents of the file named src to a file named dst. Both src and dst need to be the entire filename of the files, including path.
The destination location must be writable; otherwise, an IOError exception will be raised.
If dst already exists, it will be replaced.
Special files such as character or block devices and pipes cannot be copied with this function.
With copy, src and dst are path names given as strs.

Another shutil method to look at is shutil.copy2(). It's similar but preserves more metadata (e.g. time stamps).

If you use os.path operations, use copy rather than copyfile. copyfile will only accept strings.