Tail implementation in python

tail.py

import io, sys, itertools

def tail(file, line_count):
  BUFFER_SIZE = 1024
  pos = -BUFFER_SIZE
  offset = 0
  result_lines = []
  result_line_count = 0
  while result_line_count < line_count:
    file.seek(pos, io.SEEK_END)
    text = file.read(BUFFER_SIZE + offset)
    try:
      offset = text.index(b'\n')
    except ValueError:
      offset = len(text)
      pos = pos - BUFFER_SIZE
      continue
    lines = text.splitlines()[1:]
    line_to_add = line_count - len(result_lines)
    if len(lines) >= line_to_add:
      result_lines.append(lines[-line_to_add:len(lines)])
    else:
      result_lines.append(lines)
    result_line_count+=len(lines)
    pos = pos - BUFFER_SIZE
  
  result_lines.reverse()
  flatten = list(itertools.chain.from_iterable(result_lines))
  return b'\n'.join(flatten).decode('utf-8')


if __name__ == '__main__':
  filename = sys.argv[1]
  line = int(sys.argv[2])
  with io.open(filename, 'br') as file:
    print(tail(file, line))