Source Code for Module ZenUtils.Driver

  1  ########################################################################### 
  2  # 
  3  # This program is part of Zenoss Core, an open source monitoring platform. 
  4  # Copyright (C) 2007, Zenoss Inc. 
  5  # 
  6  # This program is free software; you can redistribute it and/or modify it 
  7  # under the terms of the GNU General Public License version 2 as published by 
  8  # the Free Software Foundation. 
  9  # 
 10  # For complete information please visit: http://www.zenoss.com/oss/ 
 11  # 
 12  ########################################################################### 
 13  #! /usr/bin/env python  
 14   
 15  __doc__='''Driver.py 
 16   
 17  Run generators that produce Deferreds. 
 18   
 19  twisted.flow has something like this, except I cannot understand it. 
 20   
 21  $Id$ 
 22  ''' 
 23   
 24  __version__ = "$Revision$"[11:-2] 
 25   
 26   
 27  from twisted.internet import defer, reactor 
 28  from twisted.python import failure 
 29   
 30 -class Driver: 
 31      "Walk an iterable that returns a deferred." 
 32       
 33 -    def __init__(self): 
 34          self.defer = defer.Deferred() 
 35          self.result = None 
 36   
 37 -    def drive(self, iterable): 
 38          "Call the iterable and set up callbacks to finish" 
 39          self.iter = iterable 
 40          self._next() 
 41          return self.defer 
 42   
 43 -    def _next(self): 
 44          "Move on to the next iterable value" 
 45          try: 
 46              self.iter.next().addBoth(self._finish) 
 47          except StopIteration: 
 48              self.defer.callback(self.result) 
 49          except Exception, ex: 
 50              self.defer.errback(failure.Failure(ex)) 
 51   
 52 -    def next(self): 
 53          "Provide the result of the iterable as a value or exception" 
 54          ex = self.result 
 55          if isinstance(self.result, failure.Failure): 
 56              ex = self.result.value 
 57          if isinstance(ex, Exception): 
 58              raise ex 
 59          return self.result 
 60   
 61 -    def _finish(self, result): 
 62          "Store the result of the last deferred for use in next()" 
 63          self.result = result 
 64          self._next() 
 65   
 66 -def drive(callable): 
 67      '''Typical use of Driver class: 
 68   
 69      def walk(driver): 
 70          yield thing1() 
 71          print "Thing 1 is", driver.next() 
 72          yeild thing2() 
 73          print "Thing 2 is", driver.next() 
 74   
 75      drive(walk) 
 76   
 77      ''' 
 78      d = Driver() 
 79      return d.drive(callable(d)) 
 80   
 81   
 82 -def driveLater(secs, callable): 
 83      "Drive the callable at a later time" 
 84      d = defer.Deferred() 
 85      def driveAgain(): 
 86          drive(callable).chainDeferred(d) 
 87      reactor.callLater(secs, driveAgain) 
 88      return d 
 89   
 90   
 91 -def test(): 
 92      lst = [] 
 93      def loop(d): 
 94          for i in range(10): 
 95              yield defer.succeed(i) 
 96              lst.append(d.next()) 
 97      def final(v): 
 98          assert lst[-1] == v 
 99      drive(loop).addCallback(final) 
100      assert lst == range(10) 
101      def unloop(d): 
102          yield defer.fail(ZeroDivisionError('hahaha')) 
103          d.next() 
104      def checkError(err): 
105          assert isinstance(err.value, ZeroDivisionError) 
106      drive(unloop).addErrback(checkError) 
107           
108   
109  if __name__ == '__main__': 
110      test() 
111