python-2.7 - Delete Duplicate records in CSV file in python 2.7

Question

My INPUT file:

1,boss,30
2,go,35
2,nan,45
3,fog,33
4,kd,55
4,gh,56

Output file should be:

1,boss,30
3,fog,33

Means my output file should be free from duplicates. I should delete the record which is repeating based on the column 1.

Code I tried:

source_rd = csv.writer(open("Non_duplicate_source.csv", "wb"),delimiter=d)
gok = set()
for rowdups in sort_src:
    if rowdups[0] not in gok:
        source_rd.writerow(rowdups)
        gok.add( rowdups[0])

Output I got:

1,boss,30
2,go,35
3,fog,33
4,kd,55

What am I doing wrong?