Simple Python script for merging rows in a CSV based on some key column.

csv_merge.py

#!/usr/bin/env python

import csv
import sys

records = {}

keyfield = sys.argv[2]

with file(sys.argv[1], 'rU') as f:
    reader = csv.DictReader(f)
    for row in reader:
        rec = records.setdefault(row[keyfield], {})
        for k, v in row.iteritems():
            if v:
                rec[k] = v

    writer = csv.DictWriter(sys.stdout, reader.fieldnames)
    writer.writeheader()
    writer.writerows(records.values())