python 日志增量抓取实现方法

import time
import pickle
import os
import re
class LogIncScaner(object):
  def __init__(self,log_file, reg_ex,seek_file='/tmp/log-inc-scan.seek.temp'):
    self.log_file = log_file
    self.reg_ex = reg_ex
    self.seek_file = seek_file
  def scan(self):
    seek = self._get_seek()
    file_mtime = os.path.getmtime(self.log_file)
    if file_mtime <= seek['time']:
      print 'file mtime not change since last scan'
      seek['time'] = file_mtime
      self._dump_seek(seek)
      return []
    file_size = os.path.getsize(self.log_file)
    if file_size <= seek['position']:
      print 'file size not change since last scan'
      seek['position'] = file_size
      self._dump_seek(seek)
      return []
    print 'file changed,start to scan'
    matchs = []
    with open(self.log_file, 'rb') as logfd:
      logfd.seek(seek['position'],os.SEEK_SET)
      for match in re.finditer(self.reg_ex, logfd.read()):
        matchs.append(match)
      seek = {'time':time.time(),'position': logfd.tell()}
      print seek
      self._dump_seek(seek)
    return matchs
  def _get_seek(self):
    seek = {'time':time.time(),'position':0}
    if os.path.exists(self.seek_file):
      with open(self.seek_file,'rb') as seekfd:
          try:
            seek = pickle.load(seekfd)
          except:
            pass
    print seek
    return seek
  def _dump_seek(self, seek):
    with open(self.seek_file,'wb') as seekfd:
      pickle.dump(seek,seekfd)
  def reset_seek(self):
    self._dump_seek({'time':time.time(),'position':0})
if __name__ == "__main__":
  scaner = LogIncScaner('/var/log/messages',r'(\w+ \d+ \d+:\d+:\d+) .+?exception')
  scaner.reset_seek()
  while True:
    matchs = scaner.scan()
    for match in matchs:
      print 'fond at:' + match.group(1) + ' content:' + match.group(0)
    time.sleep(5)