Add a `check-csv` hook

[jenstroeger]

Considering the other existing check-foo file format hooks that check for basic consistencies, and knowing of question https://github.com/pre-commit/pre-commit-hooks/issues/880, I do think that there is value in a generic CSV checker, e.g. to check for text encoding or consistent column count. So I created a simple hook:

import argparse
import csv
import io
import locale
import typing

def check_csv(filename: str, encoding: str, delimiters: str) -> bool:
    try:
        with open(filename, encoding=encoding) as f:
            data = f.read()
    except UnicodeDecodeError:
        print(f'{filename}: failed to decode csv text file using {encoding!r}')
        return False

    # It seems that Dialect detection performs column check too, need to read src.
    try:
        dialect = csv.Sniffer().sniff(data, delimiters)
    except csv.Error:
        print(f'{filename}: failed to detect dialect')
        return False

    reader = csv.reader(io.StringIO(data), dialect)
    if len(set(len(row) for row in reader)) != 1:
        print(f'{filename}: contains different numbers of columns')
        return False

    return True

def main(argv: typing.Sequence[str] | None = None) -> int:
    parser = argparse.ArgumentParser()
    parser.add_argument('-e', '--encoding', dest='encoding', default=locale.getpreferredencoding())
    parser.add_argument('-d', '--delimiters', dest='delimiters', default=',\t; :')  # CPython Sniffer defaults.
    parser.add_argument('filenames', nargs='*', help='Filenames to check.')
    args = parser.parse_args(argv)

    retval = 0
    for filename in args.filenames:
        if not check_csv(filename, encoding=args.encoding, delimiters=args.delimiters):
            retval = 1
    return retval

if __name__ == '__main__':
    raise SystemExit(main())

If you’re interested, I’m happy to discuss a few details and open a PR. Thanks!

[asottile]

please search the issue tracker, this has been rejected in the past