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  Untwisting Python Network Programming
Subject:   Why untwisting?
Date:   2006-08-13 22:19:59
From:   Kendrew
Response to: Why untwisting?

Thank you for pointing out the possibility of TCP segmenting, which may cause problems to dataReceived.

Regarding performance, I observed the core modules runs faster than Twisted when running the programs. I also briefly did some measurements and here are the results:

Using core modules:
start server (no net): 0.6040 sec
send mails (smtp): 1.5585 sec
view mails (pop3): 0.7506 sec
delete mails (pop3): 0.5159 sec
stop server (telnet): 0.5063 sec

Using Twisted:
start server (no net): 0.6668 sec
send mails (smtp): 2.4919 sec
view mails (pop3): 1.4418 sec
delete mails (pop3): 1.2992 sec
stop server (telnet): 2.1045 sec

(Windows XP, Python 2.4.3, Twisted 2.4.0)

These numbers are the average of 10 runs, and the mail server is run in localhost. While the measurements are by no means vigorous, they basically agree with the observations. Of course, the differences may not be significant in real uses when the network delay counts for majority of the execution time.

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Showing messages 1 through 4 of 4.

  • performance
    2006-08-14 08:16:53  radix [View]

    How were these numbers reached? Can you show us any python code or commands that you used to find them?

    I notice that your synchronous version of the telnet code immediately closes the socket whereas the twisted version is waiting for the *server* to end the connection; this could definitely be affecting your times. If you add a transport.loseConnection call after your write call, the semantics should line up better, and I imagine performance will be closer to what we expect.

    Also, why are you calling the private "_write" method in the telnet example?
    • performance
      2006-08-17 04:57:06  Kendrew [View]

      The time includes starting the interpreter and doing the whole script. It is true that the import statements (and any networking delay) contributes the majority to the execution time in these small programs. In fact, before measuring I did some tidying of the import statements so that only required items are imported before use.

      For the telnet, I measure again with the addition of transport.loseConnection() and using StatefulTelnetProtocol instead of Telnet. The Twisted telnet runs faster than before, as expected:

      Using core modules:
      start server (no net): 0.5809 sec
      send mails (smtp): 1.3601 sec
      view mails (pop3): 0.7007 sec
      delete mails (pop3): 0.5187 sec
      stop server (telnet): 0.5124 sec

      Using Twisted:
      start server (no net): 0.5959 sec
      send mails (smtp): 2.2488 sec
      view mails (pop3): 1.4274 sec
      delete mails (pop3): 1.3074 sec
      stop server (telnet): 1.3213 sec

      If you're interested, there is the Python program to measure the timing. It just invokes various usages of the two networking programs and takes the average.

      # file: mail-timeit.py
      # Measures the timing of invoking mail-core.py and mail-twisted.py

      from time import sleep
      from timeit import Timer
      cmdline = ''

      def doit(cmd, arg, array, rest):
      global cmdline
      cmdline = cmd + ' ' + arg
      print; print cmdline
      'import os; from __main__ import cmdline').timeit(1))

      def dostat(cmd, times):
      stat = [[], [], [], [], []] # for 1, s, v, d, 0

      for i in range(times):
      doit(cmd, '1', stat[0], 12)
      doit(cmd, 's', stat[1], 5)
      doit(cmd, 'v', stat[2], 1)
      doit(cmd, 'd', stat[3], 1)
      doit(cmd, '0', stat[4], 2)

      return stat

      def avgstat(stat, fr, to):
      return [ sum(i[fr:to]) / (to-fr) for i in stat ]

      def printavgs(avgs):
      labels = [
      'start server (no net)',
      'send mails (smtp)',
      'view mails (pop3)',
      'delete mails (pop3)',
      'stop server (telnet)']
      for i, j in zip(labels, avgs):
      print '%25s: %.4f sec' % (i, j)

      if __name__ == '__main__':
      times = 11

      stat1 = dostat('mail-core.py', times)
      avgs1 = avgstat(stat1, 1, times)

      stat2 = dostat('mail-twisted.py', times)
      avgs2 = avgstat(stat2, 1, times)

      # print stat1
      # print stat2

      # end of mail-timeit.py

  • Why untwisting?
    2006-08-14 08:15:01  glyph@divmod.com [View]

    Are you measuring the time it takes to perform a task, or the amount of time it takes to start the interpreter, load every module, perform the task, and shut down the interpreter?

    Twisted has more code in it than the Python standard library version, so unless you've carefully optimized the package for importing, the amount of time spent loading code will dwarf the amount of time spent actually doing anything.
    • Short examples don't show event driven-driven benefits
      2006-08-23 11:11:38  andypurshottam [View]

      The main advantages of event driven programming become visible when large amounts of data can be processed incrementally ("streaming") and when there are multiple event sources, especially a gui tooklkit. Small cute programming examples typically do not need these resources. The smallest example I have seen of a application that needs and benefits from event-driven programming is the tcp proxy spy with gui window, like tcpwatch (done with async stuff from medusa, but would be instructive example with any event-driven system.)

      Found I really understood POE after completing such a program, and would advise those trying to learn a event-driven stsrem to code such. Only proplem is that doing so is not trivial, especially given the small examples that come with most systems, that do not explain how to do the tricky things needed so code a proxy, that also has GUI or standard IO, and possibly multple network connections.

      Andy (andypurshottam@gmail.com)