Python

Part 6: And Then We Took It Higher

This continues the introduction started here. You can find an index to the entire series here.

Poetry for Everyone

We’ve made a lot of progress with our poetry client. Our last version (2.0) is using Transports, Protocols, and Protocol Factories, the workhorses of Twisted networking. But there are more improvements to make. Client 2.0 (and also 2.1) can only be used for downloading poetry at the command line. This is because the PoetryClientFactory is not only in charge of getting poetry, but also in charge of shutting down the program when it’s finished. That’s an odd job for something called “PoetryClientFactory”, it really ought to do nothing beyond making PoetryProtocols and collecting finished poems.

Part 5: Twistier Poetry

This continues the introduction started here. You can find an index to the entire series here.

Abstract Expressionism

In Part 4 we made our first poetry client that uses Twisted. It works pretty well, but there is definitely room for improvement.

First of all, the client includes code for mundane details like creating network sockets and receiving data from those sockets. Twisted provides support for these sorts of things so we don’t have to implement them ourselves every time we write a new program. This is especially helpful because asynchronous I/O requires a few tricky bits involving exception handling as you can see in the client code. And there are even more tricky bits if you want your code to work on multiple platforms. If you have a free afternoon, search the Twisted sources for “win32” to see how many corner cases that platform introduces.

Part 4: Twisted Poetry

This continues the introduction started here. You can find an index to the entire series here.

Our First Twisted Client

Although Twisted is probably more often used to write servers, clients are simpler than servers and we’re starting out as simply as possible. Let’s try out our first poetry client written with Twisted. The source code is in twisted-client-1/get-poetry.py. Start up some poetry servers as before:

python blocking-server/slowpoetry.py --port 10000 poetry/ecstasy.txt --num-bytes 30
python blocking-server/slowpoetry.py --port 10001 poetry/fascination.txt
python blocking-server/slowpoetry.py --port 10002 poetry/science.txt

And then run the client like this:

Part 3: Our Eye-beams Begin to Twist

This continues the introduction started here. You can find an index to the entire series here.

Doing Nothing, the Twisted Way

Eventually we are going to re-implement our asynchronous poetry client using Twisted. But first let’s write a few really simple Twisted programs just to get the flavor of things. As I mentioned in Part 2, I developed these examples using Twisted 8.2.0. Twisted APIs do change, but the core APIs we are going to use will likely change slowly, if at all, so I expect these examples to work for many future releases. If you don’t have Twisted installed you can obtain it here.

Part 2: Slow Poetry and the Apocalypse

This continues the introduction started here. And if you read it, welcome back. Now we’re going to get our hands dirty and write some code. But first, let’s get some assumptions out of the way.

My Assumptions About You

I will proceed as if you have a basic working knowledge of writing synchronous programs in Python, and know at least a little bit about Python socket programming. If you have never used sockets before, you might read the socket module documentation now, especially the example code towards the end. If you’ve never used Python before, then the rest of this introduction is probably going to be rather opaque.

Part 1: In Which We Begin at the Beginning

Preface

Someone recently posted to the Twisted mailing list asking for something like the “Twisted introduction for people on a deadline”. Full disclosure: this isn’t it. On the spectrum of introductions to Twisted and asynchronous programming in Python, it may be on the exact opposite end. So if you don’t have any time, or any patience, this isn’t the introduction you are looking for.

Up until recently, if I needed to launch a child process from a Python program, I would use the system() function in the os module, because it was the easiest one for me to remember how to use. This is despite the fact that system() is rarely what I actually wanted.

For starters, os.system() runs the command in a shell, so unless you are actually using the shell redirection operators or argument expansion, the function is just launching a shell in order to run the program you really wanted to start in the first place. Second, the shell is going to interpret your arguments the way shells do – splitting arguments on spaces, expanding wildcards, etc. If one of the arguments is a filename with spaces and shell special characters, you have to escape it very carefully (and in a system-specific way) to prevent the shell from messing with it. Naturally, I often just wouldn’t bother and thus my commands would fail whenever a strange filename showed up.

Okee dokey, I just finished my Python script to turn my book database into wordpress blog entries.  Instant wordpress blog history, it’s like I’ve been blogging for years! Back when it wasn’t cool.

A serviceable guide to network programming in Python.

From the title, I expected this to be a thorough reference to the standard Python modules, but instead it is a collection of sample scripts which illustrate the basic usage of the standard modules. In that respect it is similar to the Python Cookbook, but the Cookbook has better recipes and more in-depth discussions of the recipes. Also, this book only covers up to Python 2.0 and is thus somewhat out of date. For example, it covers the obsolete ‘rfc822’ module, but not the new ’email’ module. Also, this book has at least one glaring error – it claims that XML is an application of SGML, which is simply not true. XML is a full-blown meta-markup language like SGML.