Real Ultimate Programming

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Notes From PyATL 2011-11-10

Real-Time Web: Gevent and (Rick Copeland)

Brief survey of asynchronous (defined as an event loop for purposes of this talk) programming

  • AsynCore
    • In stdlib, used for stdlib SMTP server
    • Nobody cares about it anymore
  • Twisted
    • Everybody knows this is the standby for asynchronous Python
    • Callbacks hurt my brain, too, assuming you mean nested more than one or two levels
  • Stackless
    • lightweight threads for cooperative multithreading
    • Needs a custom Python, though :-(
  • Event-based green threads
    • Like Stackless, but in regular Python
    • You know when you yield.


  • Gevent is an example of the last option.
  • Unsurprisingly, you should use it for I/O thanks to the GIL.
  • spawn_link means you’re linking to a spawned greenlet?
  • Greenlet provides the green threads.
  • Sweet, glorious timeouts! Timeouts suck HARD for “real” threads.
  • Pool implementation; it’s so nice when langs/libs give you these abstractions instead of rolling your own.
  • Event looks like fairly low-level primitives, but also multiple Queue implementations. On a side note, why does everybody love talking about LIFO queues instead of Stacks.
  • The big use-case is networking. They give you “green” versions of sockets, select(), SSL, DNS, etc.
  • Good WSGI support:
    • gevent.wsgi wraps a C lib, doesn’t do streaming, pipelining, or SSL
    • gevent.pywsgi is a little slower (does 75% of the reqs/s) but is full-featured.

The “Real-Time Web”

  • No page refreshes
  • Server push
  • Examples: Chat, analytics, etc.
  • Implementations: Flash, polling, Web Sockets, and more!
  • handles papering over all the different implementations and picking the best one based on the browser, etc.
  • There’s a Gevent library to give you support (nice!)

ZeroMQ (wonder how this fits in)

  • I watched Zed’s talk; ZeroMQ is cool.


  • ZeroMQ “sockets” are message-based, delivery is via a dedicated communication thread.
  • Supports TCP, inproc, unix, multicast transports
  • Different types of sockets: REQ/RES, PUSH/PULL, PUB/SUB, et al
  • pyzmq is great, but you need gevent_zmq for Gevent
  • Be careful when forking or otherwise using multiprocessing; Gevent and ZeroMQ both have global(ish) things.
  • VERY NICE! He’s using the module pattern in his sample JS. Hooray for high-quality sample code.


  • The slides for this talk are up on SlideShare.

Cython: Pythonesque C Extensions (Matt Hagy)

  • You need a .pyx file.
  • You can use this to get a huge perf win by using Cython, but you can also use it to just make it easier to wrap existing C libraries.
  • It’s almost a superset of Python (I wonder what prevents it from being a proper superset).
  • Special features for working with NumPy arrays.
  • Neat: a language-level feature for thread-level parallelism. Since it’s C, you don’t have to hold the GIL.

Writing Acceptance Tests with Freshen (Doug Hellmann)


Defining Tests

  • Features - they group Scenarios
  • Scenarios
    • Use Given to declare preconditions
    • Use Then to declare expected outcomes
  • Supporting Code - applies the test definitions to the application under test
  • You can use a “Background” to declare your “globals”
  • Cool feature: Python’s multi-line strings
  • The process of applying the tests to your system is interesting. I could explore this for quite a while, I think. Maybe I should show it to the QA guy at work.
  • The actual tests run inside of nose as a plugin. It detects .feature files as “Features” and processes them accordingly.
  • Parameterized testing are handled via “Scenario Outlines” (I hope it works well, because parameterized tests are a total pain in JUnit).
  • It is very new (only on v0.2), so you probably want to run with the version from GitHub.

From the Q&A

  • The error-handling, etc., seems to be much better than Lettuce, hence going with it instead of Lettuce.

Brandon Writes a Program… LIVE!

  • PyEphem is a module that Brandon maintains and sounds cool for astronomy buffs.
  • Astronomy is fun.