I have two csv files that each have 2 columns, one of them being the date. I want to add the second column of the second file to the first file, resulting a file with 3 columns.

I did it by creating a new file and appending the data to it this way:

```
import csv

coinsfile = open('total-bitcoins.csv', newline='')
pricesfile = open('market-price.csv', newline='')

coins = csv.reader(coinsfile, delimiter=',')
prices = csv.reader(pricesfile, delimiter=',')

with open('result.csv', 'w') as res:
    for coin_row, price_row in zip(coins, prices):
        line = str(coin_row[0]) + ',' + str(coin_row[1]) + ',' + str(price_row[1])
        res.append(line)

```

The code runs without any errors but the result is a csv file which is completely empty.

Where am I making the mistake, or is there a better way to do this job?