read_file_backwards_buffer_regex.py

import re
import sys
import os

def filerev(somefile, buffer=256):
  somefile.seek(0, os.SEEK_END)
  size = somefile.tell()
  lines = ['']
  rem = size % buffer
  pos = max(0, (size // buffer - 1) * buffer)
  while pos >= 0:
    somefile.seek(pos, os.SEEK_SET)
    data = somefile.read(rem + buffer) + lines[0]
    rem = 0
    pos -= buffer
    lines = re.findall(r'[^\n]*\n?', data)
    ix = len(lines) - 2
    while ix > 0:
      yield lines[ix]
      ix -= 1
  else:
    yield lines[0]

with open(sys.argv[1], 'r') as f:
  for line in filerev(f):
    sys.stdout.write(line)