I have 2 csv files with data about primers for PCR. The first file has data concerning the forward primers, and the second is data for the reverse primers. Each file has 10 rows and about 20 columns, and I would like to take each row and make a third .csv with every combination when combining rows from file 1 and file 2. So the file should be 100 rows and 40 columns. 
so the file should look something like this
row 1: forward1, reverse1.
row 2: forward1, reverse2.
row 3: forward1, reverse3.
....
row 41: forward5, reverse1 .
all the way to forward10, reverse10

Here's my code: 

```
with open(forwards) as f_csv:
    read_forward = csv.reader(f_csv)

    with open(reverses) as r_csv:
        read_reverse = csv.reader(r_csv)

        file_name = "Combinations Matrix.csv"
        f = open(file_name, 'w')

        for fwd in read_forward:
            for rev in read_reverse:               
                for f_value in fwd:
                    f.write(f_value + ',')                  
                for r_value in rev:
                  f.write(r_value + ',')              
                f.write('\n')
f.close()
print('done')

```

It is working perfectly for the first time through the outer loop. In other words, the first time through the "read\_forward" loop. But I can't figure out why when it starts the second loop of "read\_forward", it won't write the combinations like it does on the first time through. Using print statements to the console, I figured out that it's still looping through the rows of the first file, but it seems like it's not executing the inner for loops again. Can someone help me figure this out?

Thanks!