The Python MU* Development Library

Evennia Dev Blog

Various Evennia- and MUD-related musings by Griatch, the Evennia lead developer.

Imaginary Realities is back
- December 16, 2013

The Imaginariy Realities webzine was the place to go to for MUD game design articles in the late 90's. Last released in 2001, its articles are still worth the read for any game designers today.

But guess what - this venerable ezine has now returned! You can find the new issue here.

I think this is a good community initiative worthy of support. I contibuted two articles myself (one of which is about Evennia) and would like to thank the staff/editors who took their work very seriously and did sterling work on getting everything in shape.

Thanks also to the other authors who penned some very interesting articles. Great job guys!

My impressions:

  • KaVir elaborates in A modern interface for a modern MUD on the advantages of not sticking with an outdated UI just for the sake of it. Adding a more accessible presentation is not that hard and won't ruin your game but rather help it. Whereas I have read his argument about this before, this is a good summary to take to heart. Evennia's javascript web client is currently mainly a telnet clone; there's a lot of things we could offer to make it easier for users to offer a more graphical presentation.

  • Molly O’Hara, in her A well built zone is a work of art, outlines a list of useful things to keep in mind when designing a zone. While some of these vary with game type, others do not. I like the suggestion that scripting bugs need not be the most important aspect - syntactic errors can be handled by automated means as long as the design aspect of the zone is solid.

  • A journey through Paradice [sic] is Matthew Chaplain's entry on designing a dice-roller using the telnet protocol. Some interesting things here, including making creative use of the telnet character-mode and VT100 control sequences. This ties a bit into KaVir's article, in that the interface used for "modern" MUDs are often voefully missing out on a lot of possibilities.

  • Blind accessibility: challenges and opportunities by Matthew “Chaos” Sheahan, is based on interviews with a blind mudder and a game admin having implemented lots of support for seeing-impaired players. This was a really interesting article since I've been pondering myself what could be done from Evennia's core side to help players support players using screen readers. Most seem to be down to configuration options though, and avoiding making colour or ascii art the only sources of information. These are all things Evennia devs implement depend on their game. We may offer some good contribs to build from though.

  • Evennia: an introduction - this is mine. It not-so-briefly sums up stuff about Evennia and the more important systems it relies on.

  • Getting a roleplaying scene going - another article of mine. This is a light-hearted list of tropes for getting a RP scene going on an RP-mud. It's based on things I've tried or seen myself in play.

  • Darcie “Natilena” Laur laments on the often opaque newbie guides in Introducing new players and redesigning MUD School. It describes how she tested (and improved) her own MUD's starter area while testing it on her kids. It made me think more on having Evennia offering easier ways to dump text logs in all sorts of situations. And we find out that kids have the attention span of zombie squirrels - something new learned every day!

  • Finally, The Hunger Game, or how I learned to break the ship from the bottle is Michael “Drakkos” Heron's epic about his journey developing and releasing his zombie-survival MUD Epitaph. Drakkos is a frequent blogger on the MUD-planet feed, so I knew some of this already, but it's a good read and contains some useful warnings and things-to-think-of for those thinking of starting their own MUD project. We already give some of the same advice (albeit with fewer words) in our wiki but I'm seriously considering linking to Drakkos post from there as well - it gives a more comprehensive treatment and offers a real-world example of the long road to a released game.

The issue also contains a call to help recover old MUDing resources that has gone offline since their heyday. Having browsed through the classic MUD-dev mailing list archives I can agree they are not quite as easily searchable as could be hoped. It would also be great to see the old comment posts tied to the articles of the old Imaginary Realities articles, if those could be found somehow.

This is actually one thing which I do miss with this first Imaginary Realities issue - a way for readers to comment on the articles. This would likely mean a much higher level of complexity and work though, so I can certainly see why it's not there - using the existing MUD forums is probably enough for now.

Anyway, I'm happy to see this thing getting off on a good start. I'm already looking forward to the next issue!

Out of band mergings
- November 28, 2013

As of today the development repository of Evennia, which has been brewing for a few months now, merged into the main repository. This update grew from one experimental feature to a relatively big update in the end. Together with the "many-character-per-player" feature released earlier, this update covers all the stuff I talked about in my Behind the Scenes blog post.

  • Evennia's webserver was moved from Portal to Server. This moves all database-modifying operations into the same process and neatly avoids race conditions when modifying a game world from various interfaces.

  • The OOB (Out Of Band) handler was implemented. This goes together with a protocol for telnet sub-negotiations according to the MSDP specification. The handler allows on-demand reporting whenever database fields update. It also offers regular polling of properties if needed. A user can customize which oob commands are available to the client and write whatever handlers are needed for their particular game. In the future we'll also add support for GMCP, but the lack of a central, official specification is off-putting (if there is a central document besides accounts of how individual games chose to implement GMCP, please let me know). For our own included web client, we'll likely just use JSON straight off.

  • Our channel system is now typeclassed. If you are not familiar with Evennia this won't mean much to you - In short it means developers will be able to customize their channel system much easier than in the past since a channel can be treated pretty much like any Python class (thanks go to user Kelketek who actually did the implementation).

  • We added the concept of Tagging, as a more generalized version of our old Alias system. Tagging is just what it sounds like - it allows you to tag all your objects in order to group them and easily (and efficiently) find them later. Tagging offers a powerful way to create what other code bases refer to as "zones". There are many other possible uses though, such as having effects appear only in certainly tagged rooms, indicate which Characters have joined a particular guild and so on.

  • Behind the scenes there were a lot of cleanups, along with minor API changes mentioned on the mailing list. A slew of older Issues were also fixed with this merge.

Now, in the immediate future we'll be working on updating the documentation. Evennia prides itself with having a large body of documentation and this update comes with small changes to various existing systems. There are also a few bigger new features (such as OOB). No doubt the near future will also see other issues popping up as more people try things out.

Imaginary Realities update

Apparently the reboot of Imaginary Realities (to which I contribute two articles) has been pushed forward a week or two. Reason being, apparently, to finalize the actual presentation of the content. I already signed off on the last editorial fixes way before deadline, so I guess it's just to wait and see what comes of it!

A list of Evennia topics
- October 22, 2013

Some Evennia updates.


Lots of work has been happening in the dev-clone of Evennia over the last few months.

As alluded to in the last blog, the main work has been to move Evennia's webserver component into the Server-half of Evennia for various reasons, the most obvious one to make sure that all database writes happen in the same process, avoiding race conditions. But this move lead to a rework of the cache system, which in turn lead to me having to finalize the plans for how Out-of-Band protocols should be implemented server-side. And once that was finalized, OOB was pretty much implemented anyway. As part of making sure OOB trackers were updated correctly at all times meant reworking some of the ways data is stored ... So one thing led to another making this a bigger update than originally planned.

I plan to make a more detailed post to the mailing list soon with more technical details of the (relatively minor) API changes existing users should expect. The merging of the clone into the main repo is still a little way off, but adventurous users have already started testing things.

Google Code

I like Google Code. It's easy to manage and maintain, it has a good wiki and Issue system, not to mention that it allows the use of Mercurial. But in the beginning of September, suddenly all links to our user's clone repositories were gone from the front of the project page_._ Not only that, creating new clones just didn't work anymore.

Now any site can have bugs, and we made an issue for it (other projects were similarly affected). But nothing happened for the longest time - at least two months given that we didn't report it right away. Just recently the functionality came back but there is no confirmation or comments from Google (our issue is not even closed).

That such a fundamental feature can go unheeded for so long is disturbing to me, driving home the fact that Google is certainly not putting much priority in their code hosting.


Some furious activity in the IRC chat lately, with new people dropping in to chat and ask about Evennia. For example, an enthusiastic new user learned not only about Evennia but also Python for the first time. It was a lot of fun to see him go from having no programming experience except mush softcode to doing advanced Evennia system implementations in the course of a week and offering good feedback on new features in two. Good show! The freedom you get upgrading from something like softcode to Evennia's use of a full modern programming language was seemingly quite eye-opening.

Other discussions have concerned the policies around using clones/branches for development as well as the benefits of some other hosting solution. Nothing has been decided on this. There is however now also an official GitHub mirror of Evennia's main repo to be found here.

Imaginary Realities

The deadline for entering articles for the Imaginary Realities web zine reboot has passed. It's a good initiative to bring this back - the original (archived) webzine remains a useful mud-creation resource to this day. I entered two articles, one about Evennia and another about general mud-roleplaying. It will be fun to see how it comes out, apparently the first issue will appear Nov 13

One to Many
- May 13, 2013

As of yesterday, I completed and merged the first of the three upcoming Evennia features I mentioned in my Churning Behind the Scenes blog post: the "Multiple Characters per Player" feature.

Evennia makes a strict division between Player (this is an object storing login-info and represents the person connecting to the game) and their Character (their representation in-game; Characters are just Objects with some nice defaults). When you log into the game with a client, a Session tracks that particular connection.

Previously the Player class would normally only handle one Session at a time. This made for an easy implementation and this behavior is quite familiar to users of many other mud code bases. There was an option to allow more than one Session, but each were then treated equally: all Sessions would see the same returns and the same in-game entities were controlled by all (and giving the quit command from one would kick all out).

What changed now is that the Player class will manage each Session separately, without interfering with other Sessions connected to the same Player. Each Session can be connected, through the Player, to an individual Character. So multiple Characters could in principle be controlled simultaneously by the same real-world player using different open mud clients. This gives a lot of flexibility for games supporting multi-play but also as a nice way to transparently puppet temporary extras in heavy roleplaying games.

It is still possible to force Evennia to accept only one Session per Player just like before, but this is now an option, not a limitation. And even in hardcore one-character-at-a-time roleplaying games it is nice for builders and admins to be able to have separate staff or npc characters without needing a separate account for each.

This feature took a lot more work than I anticipated - it consitutes a lot of under-the-hood changes. But it also gave me ample opportunity to fix and clean up older systems and fix bugs. The outcome is more consistency and standardization in several places. There are plenty of other noteworthy changes that were made along the way in the dev branch along with some API changes users should be aware of.

So if you are an Evennia game developer you should peek at the more detailed mailing list  announcement on what has changed. The wiki is not updated yet, that will come soon.

Now onward to the next feature!

Churning behind the scenes
- January 29, 2013

At the moment there are several Evennia projects churning along behind the scenes, none of which I've yet gotten to the point of pushing into a finished state.  Apart from bug fixes and other minor things happening, these are the main updates in the pipeline at the moment.

Multiple Characters per Player/Session

Evennia has for a long time enforced a clean separation between the Player and the Character. It's a much appreciated feature among our users. The Player is "you", the human playing the game. It knows your password, eventual user profile etc. The Character is your avatar in-game. This setup makes it easy for a Player to have many characters, and to "puppet" characters - all you need to do is "disconnect" the Player object from the Character object, then connect to another Character object (assuming you are allowed to puppet that object, obviously). So far so good.

What Evennia currently doesn't support is being logged in with different client sessions to the same Player/account while puppeting multiple characters at the same time. Currently multiple client sessions may log into the same Player account, but they will then all just act as separate views of the same action (all will see the same output, you can send commands from each but they will end up with the same Character).

Allowing each session to control a separate Character suggests changing the way the session is tracked by the player and Character. This turns out to be more work than I originally envisioned when seeing the feature request in the issue tracker. But if my plan works out it will indeed become quite easy to use Evennia to both allow multi-play or not as you please, without having to remember separate passwords for each Character/account.

Webserver change to Server level

Evennia consists of two main processes, the Portal and the Server. The details of those were covered in an earlier blog post here. Evennia comes with a Twisted-based webserver which is currently operating on the Portal level. This has the advantage of not being affected by Server-reboots. The drawback is however that being in a different process from the main Server, accessing the database and notably its server-side caches becomes a problem - changing the database from the Portal side does not automatically update the caches on the Server side, telling them that the database has changed. Also writing to the database from two processes may introduce race conditions.

For our simple default setup (like a website just listing some database statistics) this is not a terrible problem, but as more users start to use Evennia, there is a growing interest in more advanced uses of the webserver. Several developers want to use the webserver to build game-related rich website experiences for their games - online character generation, tie-in forums and things like that. Out-of-sync caches then becomes a real concern.

One way around this could be to implement a framework (such as memcached) for homogenizing caches across all Evennia processes. After lots of IRC discussions I'm going with what seems to be the more elegant and clean solution though - moving the webserver into the Server process altogether. The Portal side will thus only hold a web proxy and the webclient protocol. This way all database access will happen from the same process simplifying things a lot. It will make it much easier for users to use django to create rich web experiences without having to worry about pesky behind the scenes things like caches and the like.

Out-of-band communication

This has been "brewing" for quite some time, I've been strangely unmotivated to finalize it. Out of band communication means the MUD client can send and receive data to/from the server directly, without the player having to necessesarily enter an active command or see any immediate effect. This could be things like updating a health bar in a client-side GUI, redirect text to a specific client window but also potentially more advanced stuff. I created the Evennia-side oob-handler over Christmas; it allows for client sessions to "sign up" for "listening" to attribute updates, do scheduled checks and so on. It's already in the codebase but is not activated nor tested yet.

On the protocol side (for serializing data to the client) I have a MSDP implementation ready for telnet subnegotiation, it should be simple to add also GMCP once everything is tested. A JSON-based side channel for the webclient is already in place since a long time if I remember correctly, it just need to be connected to the server-side oob-handler once that's finished.