Python: replace a string in a CSV file

Question

I am a beginner and I have an issue with a short code. I want to replace a string from a csv to with another string, and put out a new csv with an new name. The strings are separated with commas.

My code is a catastrophe:

import csv

f = open('C:\\User\\Desktop\\Replace_Test\\Testreplace.csv')
csv_f = csv.reader(f)

g = open('C:\\Users\\Desktop\\Replace_Test\\Testreplace.csv')
csv_g = csv.writer(g)


findlist = ['The String, that should replaced']
replacelist = ['The string that should replace the old striong']


#the function  ?:
def findReplace(find,replace):
s = f.read()
for item, replacement in zip(findlist,replacelist):
s = s.replace(item,replacement)
g.write(s)

for row in csv_f:
print(row)

f.close()
g.close()

Could you correct the indentation please?

cs95
– cs95

2017-11-16 17:48:13 +00:00
Commented Nov 16, 2017 at 17:48 — cs95
– cs95, Commented Nov 16, 2017 at 17:48

Banzai Otis · Accepted Answer · 2017-11-16 18:12:05Z

4

You can do this with the regex package re. Also, if you use with you don't have to remember to close your files, which helps me.

EDIT: Keep in mind that this matches the exact string, meaning it's also case-sensitive. If you don't want that then you probably need to use an actual regex to find the strings that need replacing. You would do this by replacing find_str in the re.sub() call with r'your_regex_here'.

import re

# open your csv and read as a text string
with open(my_csv_path, 'r') as f:
    my_csv_text = f.read()

find_str = 'The String, that should replaced'
replace_str = 'The string that should replace the old striong'

# substitute
new_csv_str = re.sub(find_str, replace_str, my_csv_text)

# open new file and save
new_csv_path = './my_new_csv.csv' # or whatever path and name you want
with open(new_csv_path, 'w') as f:
    f.write(new_csv_str)

edited Nov 16, 2017 at 18:12

answered Nov 16, 2017 at 18:07

Banzai Otis

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2 Comments

tripleee Over a year ago

This requires the CSV file to fit into memory. A more robust solution might be to process one line at a time and write it out to a temporary file, then rename it at the end so it replaces the original if the main program completed successfully.

xjcl Over a year ago

1. This might lead to false positives if the string is a substring (e.g. ham vs chamber) 2. This could use str.replace as regex functionality is not needed

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