A simple utility class to wait until a file in the filesystem has changed.

update_watcher.py

#  Usage:
#    watcher = UpdateWatcher(changing_file_path)
#    while True:
#      watcher.wait_for_update()
#      # Do my stuff.

import os, os.path as op
import time
import logging

class UpdateWatcher():
  ''' Use this class to wait until a file is updated.
  The thread is blocked while waiting.
  '''
  def __init__(self, filepath):
    self.CallInterval = 0.05  # Wait sec after unsuccessful attempt.
    self.filepath = filepath
    self.filetime = 0

  def wait_for_update(self):
    oldfiletime = self.filetime
    filetime = op.getmtime(self.filepath)
    firsttry = time.time()
    while filetime == oldfiletime:
      logging.debug('File not changed after %.2f sec.' % (time.time() - firsttry))
      time.sleep(self.CallInterval)
      filetime = op.getmtime(self.filepath)
    self.filetime = filetime
    logging.info('Input file updated after %.2f sec.' % (time.time() - firsttry))