Insert new line in CSV at second row via Python

Question

Is it possible to insert a new line in a CSV file at the 2nd row? For example, I have a CSV with column names and their values:

meter_id, sdp_id, lat, lon
813711, 1331, 34.298, -83.113

The application I'm attempting to read this file into requires a new line added indicating the column type. In the above example all would be string, so the CSV would need to be:

meter_id, sdp_id, lat, lon
String, String, String, String
813711, 1331, 34.298, -83.113

I've read several posts how to add a new line at the end of the CSV, but couldn't find anything on how to do the above.

Possible duplicate of Insert line at middle of file with Python? — Mike Scotty
– Mike Scotty, Commented Jun 5, 2018 at 13:18

Rakesh · Accepted Answer · 2018-06-05 13:20:39Z

4

This is one approach using csv module.

Demo:

import csv
toAdd = ["String", "String", "String", "String"]
with open(filename, "r") as infile:
    reader = list(csv.reader(infile))
    reader.insert(1, toAdd)

with open(filename, "w") as outfile:
    writer = csv.writer(outfile)
    for line in reader:
        writer.writerow(line)

answered Jun 5, 2018 at 13:20

Rakesh

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4 Comments

J. Skinner Over a year ago

thank you for this answer. It's working, but it is entering an empty row between is row in the updated CSV.

Rakesh Over a year ago

Use with open(filename, "w", newline='') as outfile: if you are in python3

J. Skinner Over a year ago

I'm using Python 2.7.14.

Rakesh Over a year ago

Then use with open(filename, "wb") as outfile:

CLeo-Dev · Accepted Answer · 2018-06-05 13:22:19Z

2

A simple solution could be:

import csv

row = ['String', ' String', ' String']

with open('file.csv', 'r') as readFile:
    reader = csv.reader(readFile)
    lines = list(reader)
    lines.insert(1, row)

with open('file.csv', 'w') as writeFile:
    writer = csv.writer(writeFile)
    writer.writerows(lines)

readFile.close()
writeFile.close()

I could not try it. Please let me know if it works.

answered Jun 5, 2018 at 13:22

CLeo-Dev

2162 silver badges12 bronze badges

1 Comment

J. Skinner Over a year ago

Thanks, one thing I'm noticing is that this is adding an extra row between each row in the updated CSV.

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