replacing the first line of a csv file python

Question

I need to replace the column headings in a CSV file, where I don't know the order or number of columns. For example the file could look like this: ``` DN cn sn Name mail depart mobile data1 data2 data3 data4 data5 data6 data7 ``` or this ``` DN cn depart mobile sn data1 data2 data3 data4 data5 ``` AND I need to copy one column and create a new heading, so the final output would look something like this (notice data1 is repeated): ``` user email phone depar mobile sn data1 data1 data2 data3 data4 data5 ``` I am going 'round in circles with this one. Using ``` import csv with open('test.csv', 'rb') as csvfile: r = csv.reader(csvfile, delimiter=',', quotechar='"') headers=r.next() for index, heading in enumerate(headers): if heading == 'mail': headers[index] = "Username" ``` I can change the column headings fine, and either write it to a new file or to the existing one, but then how do I add the extra column? SOLUTION Thanks to abarnert's answer below I am now using this code which works…

Accepted Answer

All you need to do is keep track of where you found the column to be copied, then add it. For example:

```
# ...
# for ...

if heading == 'mail':
        headers[index] = "Username"
    elif heading == 'data1':
        data_1_index = index

headers.insert(data_1_index, 'data1')
```

And I assume you'll also want to copy the value in each row, too. But that's just as easy.

```
for row in r:
    row.insert(data_1_index, row[data_1_index])
    w.writerow(row)
```

Putting it all together, here's a complete program that does what (I think) you want:

```
import csv

with open('test.csv', 'rb') as infile, open('out.csv', 'wb') as outfile:
    r = csv.reader(infile, delimiter=',', quotechar='"')
    headers=r.next()
    for index, heading in enumerate(headers):
        if heading == 'mail':
            headers[index] = "Username"
        elif heading == 'data1':
            data_1_index = index
    headers.insert(data_1_index, 'data1')

w = csv.writer(outfile, delimiter=',', quotechar='"')
    w.writerow(headers)
    for row in r:
        row.insert(data_1_index, row[data_1_index])
        w.writerow(row)
```

replacing the first line of a csv file python

Solution

Problem