Prints the largest field lengths encountered in a CSV

get_max_csv_field_lengths.py

import csv
import sys
from collections import defaultdict


def print_max_field_lengths(fname):
    """
    Prints the largest field lengths encountered in the csv
    file in fname
    """
    counts = defaultdict(int)
    f = open(fname)
    with f as csvfile:
        reader = csv.DictReader(csvfile)
        for row in reader:
            for k, v in row.items():
                counts[k] = max(counts[k], len(v))

    for (k, count) in reversed(sorted(counts.items(), key=lambda x: x[1])):
        print(count, k)


if __name__ == "__main__":
    print_max_field_lengths(sys.argv[-1])