Python script to tail (like the posix tail command) a csv file which has records which span multiple lines

tailcsv.py

#!/usr/bin/env python

# tailcsv.py is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# tailcsv.py is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with tailcsv.py.  If not, see <http://www.gnu.org/licenses/>.

import argparse
import sys

class LastNItem:
    sentinal = object()

    def __init__(self, n):
        self.n = n
        self.items = [self.sentinal] * n
        self.i = -1

    def add(self, item):
        self.i += 1
        self.i %= self.n
        self.items[self.i] = item

    def getall(self):
        if self.i == -1:
            return []

        for i in range(self.i + 1, self.i + self.n + 1):
            j = i % self.n
            if self.items[j] is self.sentinal:
                continue
            else:
                yield self.items[j]


def main():
    parser = argparse.ArgumentParser(description='Tail a csv file which' 
        'has records which span multiple lines')
    parser.add_argument('-n', '--lines', type=int,
                        help='number of lines to show', required=True)
    parser.add_argument('-q', '--quotechar',
                        help='quote character used for field', default="\"")
    parser.add_argument('-ih', '--include-headers', action="store_true", default=False,
                        help='include headers')

    args = parser.parse_args()

    record = []
    inside_quote = False
    last_n_items = LastNItem(args.lines)

    first_line = args.include_headers

    parsed = bytearray()
    for line in sys.stdin.buffer.readlines():
        for c in line:
            if c == ord(args.quotechar):
                inside_quote = not inside_quote
                parsed.append(c)
            elif c == ord("\n") and not inside_quote:
                parsed.append(c)
                record.append(bytes(parsed))
                if first_line:
                    first_line = False
                    sys.stdout.buffer.writelines(record)
                else:
                    last_n_items.add(record)
                record = []
                parsed = bytearray()
            else:
                parsed.append(c)

    if len(parsed) > 0:
        record.append(bytes(parsed))

    if len(record) > 0:
        last_n_items.add(record)

    for line in last_n_items.getall():
        sys.stdout.buffer.writelines(line)


if __name__ == '__main__':
    main()