How to implement a pythonic equivalent of tail -F?

Question

What is the pythonic way of watching the tail end of a growing file for the occurrence of certain keywords?

In shell I might say:

tail -f "$file" | grep "$string" | while read hit; do     #stuff done 

Answer 1

Well, the simplest way would be to constantly read from the file, check what's new and test for hits.

import time  def watch(fn, words):     fp = open(fn, 'r')     while True:         new = fp.readline()         # Once all lines are read this just returns ''         # until the file changes and a new line appears          if new:             for word in words:                 if word in new:                     yield (word, new)         else:             time.sleep(0.5)  fn = 'test.py' words = ['word'] for hit_word, hit_sentence in watch(fn, words):     print "Found %r in line: %r" % (hit_word, hit_sentence) 

This solution with readline works if you know your data will appear in lines.

If the data is some sort of stream you need a buffer, larger than the largest word you're looking for, and fill it first. It gets a bit more complicated that way...