#!/usr/bin/env python
# Added by <ctang@redhat.com>
# Added on Sept 14 2012
'''
A pipeline made of several coroutines
that can be turned off gracefully.
This script is inspired by David Beazley with his PyCon 09 talks.
Based on his ideas, I have extended a bit to make the pipeline
able to be monitored and turned off gracefully.
'''
import time
file_name = './food.txt'
def coroutine(func):
'''A decorator that advances
the execution to the first 'yield'
in a generator so that this generator
is "primed".
'''
def generator(*args, **kwargs):
primed_func = func(*args, **kwargs)
primed_func.next()
return primed_func
return generator
def contains_word(line):
if line.find('a') > 0:
return True
return False
def turn_off_when_too_long(line):
print 'length:', len(line)
if len(line) > 200:
return True
return False
def tail(target_file, target):
'''Mimic Unix tail -f
This is the source of the pipeline
a pipeline must have a source.
'''
# Moves to the end of file
target_file.seek(0, 2)
try:
while True:
line = target_file.readline()
if line:
target.send(line)
else:
time.sleep(0.1)
continue
except StopIteration:
print "Pipeline Ended"
@coroutine
def printer():
'''Display the line
This is the end-point(sink) of the pipeline.
'''
try:
while True:
line = (yield)
print line,
except GeneratorExit:
print 'Printer Pipeline Ended'
@coroutine
def grep(pattern_check, target):
try:
while True:
line = (yield)
if pattern_check(line):
target.send(line)
else:
continue
except GeneratorExit:
print "Grep Pipeline Ended"
target.close()
@coroutine
def monitor(pattern_check, target):
while True:
line = (yield)
if pattern_check(line):
break
else:
target.send(line)
target.close()
def main():
f = open(file_name)
tail(f, monitor(turn_off_when_too_long, grep(contains_word, printer())))
if __name__ == '__main__':
main()
Diff to Previous Revision
--- revision 1 2012-09-14 09:52:43
+++ revision 2 2012-09-14 09:53:58
@@ -13,10 +13,9 @@
import time
-from utils import coroutine
-'''
-The definition of the coroutine:
+file_name = './food.txt'
+
def coroutine(func):
'''A decorator that advances
@@ -29,11 +28,6 @@
primed_func.next()
return primed_func
return generator
-'''
-
-
-file_name = './food.txt'
-
def contains_word(line):
if line.find('a') > 0:
