Skip to main content

DeferArgs lets you write syncronous looking functions that really aren't!

So a little side project for my own uses provided a simple decorator that lets me write a function I can pass deferreds and regular arguments to, and have the function return a deferred that fires when all of its deferred arguments are ready and the function has processed them. Some example usage:


@deferargs
def printArgs(*args, **kwargs):
print "Positional Arguments: ", ", ".join(args)
print "Keyword Arguments: ", ", ".join("%r=%s"%(k,v) for (k,v) in kwargs.items())

printArgs("foobar", baz=someNetworkRequest())


Really basic, but it can prove useful for a large portion of Twisted code you might write. I'm planning to add some semi-evil way to do something that looks a lot like a try/except/finally block but is actually (obviously) not, and works with any errbacks from deferreds within the try-like block of code. The reaction has been interesting. I've had some people stand up for the idea, which is similar to
defgen
, and others who think it is a bad idiom that is dangerous to encourage.

Using this kind of abstraction over asyncronous code, you do have to be careful to remember what is asyncronous and take consideration that your code won't run until all deferred arguments are ready, even if some parts could be run with only some of the arguments. In those cases, however, you should just break up the function, and I'd like to note that you can make the same mistakes using deferreds and the like directly, so I don't really see it as an issue.

If you want to do any error handling for the moment, you need to attach errbacks to the deferred from the function call. I want to work in my semi-evil error handling soon, because my goal here is to hide the fact that there are deferreds as much as possible, but for now this is just fine, and I've already had use of it myself.

You can get it from the Cheeseshop, so check it out there now and place any comments about it here.

Filed in:

Comments

Kevin Deenanauth said…
Thanks for this! I think this goes a long way toward making Twisted code more readable (and Pythonic =)

The concerns for this is understandable, but if you know how Twisted works, then there shouldn't be a problem.
Anonymous said…
This is very cool. I don't think it is counter to the way twisted processing flow really works at all.

Popular posts from this blog

Why I Switched From Git to Microsoft OneDrive

I made the unexpected move with a string of recent projects to drop Git to sync between my different computers in favor of OneDrive, the file sync offering from Microsoft. Its like Dropbox, but "enterprise."

Feeling a little ashamed at what I previously would have scoffed at should I hear of it from another developer, I felt a little write up of the why and the experience could be a good idea. Now, I should emphasize that I'm not dropping Git for all my projects, just specific kinds of projects. I've been making this change in habit for projects that are just for me, not shared with anyone else. It has been especially helpful in projects I work on sporadically. More on why a little later.

So, what drove me away from Git, exactly?

On the smallest projects, like game jam hacks, I just wanted to code. I didn't want to think about revisions and commit messages. I didn't need branching or merges. I didn't even need to rollback to another version, ever. I just …

Respect and Code Reviews

Code Reviews in a development team only function best, or possible at all, when everyone approaches them with respect. That’s something I’ve usually taken for granted because I’ve had the opportunity to work with amazing developers who shine not just in their technical skills but in their interpersonal skills on a team. That isn’t always the case, so I’m going to put into words something that often exists just in assumptions.
You have to respect your code. This is first only because the nature and intent of code reviews are to safeguard the quality of your code, so even having code reviews demonstrates a baseline of respect for that code. But, maybe not everyone on the team has the same level of respect or entered a team with existing review traditions that they aren’t acquainted with.
There can be culture shock when you enter a team that’s really heavy on code reviews, but also if you enter a team or interact with a colleague who doesn’t share that level of respect for the process or…

CARDIAC: The Cardboard Computer

I am just so excited about this.


CARDIAC. The Cardboard Computer. How cool is that? This piece of history is amazing and better than that: it is extremely accessible. This fantastic design was built in 1969 by David Hagelbarger at Bell Labs to explain what computers were to those who would otherwise have no exposure to them. Miraculously, the CARDIAC (CARDboard Interactive Aid to Computation) was able to actually function as a slow and rudimentary computer. 
One of the most fascinating aspects of this gem is that at the time of its publication the scope it was able to demonstrate was actually useful in explaining what a computer was. Could you imagine trying to explain computers today with anything close to the CARDIAC?

It had 100 memory locations and only ten instructions. The memory held signed 3-digit numbers (-999 through 999) and instructions could be encoded such that the first digit was the instruction and the second two digits were the address of memory to operate on. The only re…