I have a csv that contains just 1 column of domain names that range from about 300 to 1500 lines, looking similar to the following:

```
google.com
abc.net
yahoo.com
cnn.com
twitter.com

```

All I need to do is add a column header of "domain" so my csv will look like:

```
domain
google.com
abc.net
yahoo.com
cnn.com
twitter.com

```

I attempted the following using pandas:

```
from pandas import read_csv
x = read_csv('domains.csv')
x.columns = ['domain']
x.to_csv('out.csv')

```

This results in a csv with the added column header, but it also added an additional column with the row numbers, which I don't want... what am I doing wrong?

```
    domain
0   google.com
1   abc.net
2   yahoo.com
3   cnn.com
4   twitter.com

```