Python function to offer "tail -F"-like functionality in Python

follow_file.py

'''
follow_file.py
Written April 13, 2014 by Josiah Carlson

Released under the MIT license.

This could likely be made more efficient with the use of the pyinotify library,
and some of the module-level constants could be tuned for better performance,
depending on your platform.
'''

import os
import time

CHUNKSIZE = 2**20
ZERO_READ_CHECK = 10
ZERO_READ_SLEEP = .001 # in seconds

def file_follower(fname, callback, offset=0):
    '''
    This function will read from the file provided by `fname` until it has been
    replaced. Each chunk of data that is read is passed to the provided
    `callback(offset, chunk)`, where `offset` is the position in the file from
    where the chunk of data was read from.

    You can provide an optional starting `offset` if you would like to
    continue reading from an arbitrary position.
    '''
    while 1:
        with open(fname, 'rb') as inp:
            if offset:
                # pick up where you left off
                inp.seek(offset)

            no_data = 0
            while 1:
                # read a chunk
                chunk = inp.read(CHUNKSIZE)
                if chunk:
                    # send the chunk to the callback
                    callback(offset, chunk)
                    no_data = 0
                    offset += len(chunk)
                    continue

                no_data += 1
                if not no_data % ZERO_READ_CHECK:
                    # check for file replacement
                    if os.stat(fname).st_size < offset:
                        # signals that this file is done
                        callback(offset, "")
                        break
                # maybe just a slow writer, pause for a bit
                time.sleep(ZERO_READ_SLEEP)

        # start from the beginning with the new file
        offset = 0