Re-format a bunch of CSVs into one giant CSV with all fields

normalize_csv.py

import csv
import sys

all_keys = []
for filename in sys.argv[1:]:
    with open(filename) as csvfile:
        reader = csv.DictReader(csvfile)
        for new_key in reader.fieldnames:
            if new_key not in all_keys:
                all_keys.append(new_key)

writer = csv.DictWriter(sys.stdout, all_keys)
writer.writeheader()
for filename in sys.argv[1:]:
    with open(filename) as csvfile:
        reader = csv.DictReader(csvfile)
        expanded_row = dict.fromkeys(all_keys, '')
        for row in reader:
            expanded_row.update(row)
            writer.writerow(expanded_row)