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Viewing changes to vendor/Twisted-10.0.0/doc/core/howto/listings/deferred/deferred_ex1b.py

  • Committer: Jesse Andrews
  • Date: 2010-05-28 06:05:26 UTC
  • Revision ID: git-v1:bf6e6e718cdc7488e2da87b21e258ccc065fe499
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vendor/Twisted-10.0.0/doc/core/howto/listings/deferred/deferred_ex1b.py
 
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#!/usr/bin/env python
 
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# Copyright (c) 2009 Twisted Matrix Laboratories.
 
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# See LICENSE for details.
 
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from twisted.internet import defer
 
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from twisted.python import failure, util
 
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"""
 
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Here we have a slightly more involved case. The deferred is called back with a
 
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result. the first callback returns a value, the second callback, however
 
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raises an exception, which is handled by the errback.
 
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"""
 
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class Counter(object):
 
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    num = 0
 
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def handleFailure(f):
 
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    print "errback"
 
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    print "we got an exception: %s" % (f.getTraceback(),)
 
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    f.trap(RuntimeError)
 
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def handleResult(result):
 
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    Counter.num += 1
 
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    print "callback %s" % (Counter.num,)
 
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    print "\tgot result: %s" % (result,)
 
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    return "yay! handleResult was successful!"
 
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def failAtHandlingResult(result):
 
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    Counter.num += 1
 
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    print "callback %s" % (Counter.num,)
 
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    print "\tgot result: %s" % (result,)
 
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    print "\tabout to raise exception"
 
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    raise RuntimeError, "whoops! we encountered an error"
 
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def behindTheScenes(result):
 
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    if not isinstance(result, failure.Failure): # ---- callback
 
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        try:
 
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            result = handleResult(result)
 
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        except:
 
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            result = failure.Failure()
 
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    else:                                       # ---- errback
 
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        pass
 
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    if not isinstance(result, failure.Failure): # ---- callback
 
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        try:
 
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            result = failAtHandlingResult(result)
 
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        except:
 
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            result = failure.Failure()
 
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    else:                                       # ---- errback
 
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        pass
 
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    if not isinstance(result, failure.Failure): # ---- callback
 
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        pass
 
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    else:                                       # ---- errback
 
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        try:
 
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            result = handleFailure(result)
 
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        except:
 
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            result = failure.Failure()
 
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def deferredExample():
 
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    d = defer.Deferred()
 
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    d.addCallback(handleResult)
 
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    d.addCallback(failAtHandlingResult)
 
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    d.addErrback(handleFailure)
 
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    d.callback("success")
 
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if __name__ == '__main__':
 
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    behindTheScenes("success")
 
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    print "\n-------------------------------------------------\n"
 
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    Counter.num = 0
 
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    deferredExample()