For most games it is a good idea to restrict what people can do. In Evennia such restrictions are applied and checked by something called locks. All Evennia entities (Commands, Objects, Scripts, Accounts, Help System, messages and channels) are accessed through locks.
A lock can be thought of as an “access rule” restricting a particular use of an Evennia entity. Whenever another entity wants that kind of access the lock will analyze that entity in different ways to determine if access should be granted or not. Evennia implements a “lockdown” philosophy - all entities are inaccessible unless you explicitly define a lock that allows some or full access.
Let’s take an example: An object has a lock on itself that restricts how people may “delete” that
object. Apart from knowing that it restricts deletion, the lock also knows that only players with
the specific ID of, say,
34 are allowed to delete it. So whenever a player tries to run
on the object, the
delete command makes sure to check if this player is really allowed to do so.
It calls the lock, which in turn checks if the player’s id is
34. Only then will it allow
to go on with its job.
Setting and checking a lock¶
The in-game command for setting locks on objects is
> lock obj = <lockstring>
<lockstring> is a string of a certain form that defines the behaviour of the lock. We will go
into more detail on how
<lockstring> should look in the next section.
Code-wise, Evennia handles locks through what is usually called
locks on all relevant entities.
This is a handler that allows you to add, delete and check locks.
One can call
locks.check() to perform a lock check, but to hide the underlying implementation all
objects also have a convenience function called
access. This should preferably be used. In the
accessing_obj is the object requesting the ‘delete’ access whereas
obj is the
object that might get deleted. This is how it would look (and does look) from inside the
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if not obj.access(accessing_obj, 'delete'): accessing_obj.msg("Sorry, you may not delete that.") return
Defining a lock (i.e. an access restriction) in Evennia is done by adding simple strings of lock
definitions to the object’s
locks property using
Here are some examples of lock strings (not including the quotes):
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delete:id(34) # only allow obj #34 to delete edit:all() # let everyone edit # only those who are not "very_weak" or are Admins may pick this up get: not attr(very_weak) or perm(Admin)
Formally, a lockstring has the following syntax:
access_type: [NOT] lockfunc1([arg1,..]) [AND|OR] [NOT] lockfunc2([arg1,...]) [...]
 marks optional parts.
NOT are not case sensitive and excess spaces are
lockfunc1, lockfunc2 etc are special lock functions available to the lock system.
So, a lockstring consists of the type of restriction (the
access_type), a colon (
:) and then an
expression involving function calls that determine what is needed to pass the lock. Each function
NOT work as they do normally in Python. If the
total result is
True, the lock is passed.
You can create several lock types one after the other by separating them with a semicolon (
the lockstring. The string below yields the same result as the previous example:
delete:id(34);edit:all();get: not attr(very_weak) or perm(Admin)
access_type, the first part of a lockstring, defines what kind of capability a lock controls,
such as “delete” or “edit”. You may in principle name your
access_type anything as long as it is
unique for the particular object. The name of the access types is not case-sensitive.
If you want to make sure the lock is used however, you should pick
access_type names that you (or
the default command set) actually checks for, as in the example of
delete above that uses the
Below are the access_types checked by the default commandset.
cmd- this defines who may call this command at all.
control- who is the “owner” of the object. Can set locks, delete it etc. Defaults to the creator of the object.
call- who may call Object-commands stored on this Object except for the Object itself. By default, Objects share their Commands with anyone in the same location (e.g. so you can ‘press’ a
Buttonobject in the room). For Characters and Mobs (who likely only use those Commands for themselves and don’t want to share them) this should usually be turned off completely, using something like
examine- who may examine this object’s properties.
delete- who may delete the object.
edit- who may edit properties and attributes of the object.
view- if the
lookcommand will display/list this object
get- who may pick up the object and carry it around.
puppet- who may “become” this object and control it as their “character”.
attrcreate- who may create new attributes on the object (default True)
Same as for Objects
Same as for Objects
traverse- who may pass the exit.
examine- who may examine the account’s properties.
delete- who may delete the account.
edit- who may edit the account’s attributes and properties.
msg- who may send messages to the account.
boot- who may boot the account.
Attributes: (only checked by
attrread- see/access attribute
attredit- change/delete attribute
control- who is administrating the channel. This means the ability to delete the channel, boot listeners etc.
send- who may send to the channel.
listen- who may subscribe and listen to the channel.
examine- who may view this help entry (usually everyone)
edit- who may edit this help entry.
So to take an example, whenever an exit is to be traversed, a lock of the type traverse will be
checked. Defining a suitable lock type for an exit object would thus involve a lockstring
traverse: <lock functions>.
As stated above, the
access_type part of the lock is simply the ‘name’ or ‘type’ of the lock. The
text is an arbitrary string that must be unique for an object. If adding a lock with the same
access_type as one that already exists on the object, the new one override the old one.
For example, if you wanted to create a bulletin board system and wanted to restrict who can either read a board or post to a board. You could then define locks such as:
This will create a ‘read’ access type for Characters having the
Player permission or above and a
‘post’ access type for those with
Admin permissions or above (see below how the
function works). When it comes time to test these permissions, simply check like this (in this
obj may be a board on the bulletin board system and
accessing_obj is the player
trying to read the board):
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if not obj.access(accessing_obj, 'read'): accessing_obj.msg("Sorry, you may not read that.") return
A lock function is a normal Python function put in a place Evennia looks for such functions. The
modules Evennia looks at is the list
settings.LOCK_FUNC_MODULES. All functions in any of those
modules will automatically be considered a valid lock function. The default ones are found in
evennia/locks/lockfuncs.py and you can start adding your own in
You can append the setting to add more module paths. To replace a default lock function, just add
your own with the same name.
A lock function must always accept at least two arguments - the accessing object (this is the object wanting to get access) and the accessed object (this is the object with the lock). Those two are fed automatically as the first two arguments to the function when the lock is checked. Any arguments explicitly given in the lock definition will appear as extra arguments.
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# A simple example lock function. Called with e.g. `id(34)`. This is # defined in, say mygame/server/conf/lockfuncs.py def id(accessing_obj, accessed_obj, *args, **kwargs): if args: wanted_id = args return accessing_obj.id == wanted_id return False
The above could for example be used in a lock function like this:
# we have `obj` and `owner_object` from before obj.locks.add("edit: id(%i)" % owner_object.id)
We could check if the “edit” lock is passed with something like this:
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# as part of a Command's func() method, for example if not obj.access(caller, "edit"): caller.msg("You don't have access to edit this!") return
In this example, everyone except the
caller with the right
id will get the error.
**syntax causes Python to magically put all extra arguments into a list
argsand all keyword arguments into a dictionary
kwargsrespectively. If you are unfamiliar with how
**kwargswork, see the Python manuals).
Some useful default lockfuncs (see
src/locks/lockfuncs.py for more):
true()/all()- give access to everyone
false()/none()/superuser()- give access to none. Superusers bypass the check entirely and are thus the only ones who will pass this check.
perm(perm)- this tries to match a given
permissionproperty, on an Account firsthand, on a Character second. See below.
permbut requires a “higher” permission level than the one given.
id(num)/dbref(num)- checks so the access_object has a certain dbref/id.
attr(attrname)- checks if a certain Attribute exists on accessing_object.
attr(attrname, value)- checks so an attribute exists on accessing_object and has the given value.
attr_gt(attrname, value)- checks so accessing_object has a value larger (
>) than the given value.
attr_ge, attr_lt, attr_le, attr_ne- corresponding for
holds(objid)- checks so the accessing objects contains an object of given name or dbref.
inside()- checks so the accessing object is inside the accessed object (the inverse of
pid(num)/pdbref(num)- same as
id/dbrefbut always looks for permissions and dbrefs of Accounts, not on Characters.
serversetting(settingname, value)- Only returns True if Evennia has a given setting or a setting set to a given value.
Checking simple strings¶
Sometimes you don’t really need to look up a certain lock, you just want to check a lockstring. A
common use is inside Commands, in order to check if a user has a certain permission. The lockhandler
has a method
check_lockstring(accessing_obj, lockstring, bypass_superuser=False) that allows this.
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# inside command definition if not self.caller.locks.check_lockstring(self.caller, "dummy:perm(Admin)"): self.caller.msg("You must be an Admin or higher to do this!") return
Note here that the
access_type can be left to a dummy value since this method does not actually do
a Lock lookup.
Evennia sets up a few basic locks on all new objects and accounts (if we didn’t, noone would have
any access to anything from the start). This is all defined in the root Typeclasses
of the respective entity, in the hook method
basetype_setup() (which you usually don’t want to
edit unless you want to change how basic stuff like rooms and exits store their internal variables).
This is called once, before
at_object_creation, so just put them in the latter method on your
child object to change the default. Also creation commands like
create changes the locks of
objects you create - for example it sets the
control lock_type so as to allow you, its creator, to
control and delete the object.
More Lock definition examples¶
examine: attr(eyesight, excellent) or perm(Builders)
You are only allowed to do examine on this object if you have ‘excellent’ eyesight (that is, has
eyesight with the value
excellent defined on yourself) or if you have the
“Builders” permission string assigned to you.
open: holds('the green key') or perm(Builder)
This could be called by the
open command on a “door” object. The check is passed if you are a
Builder or has the right key in your inventory.
Evennia’s command handler looks for a lock of type
cmd to determine if a user is allowed to even
call upon a particular command or not. When you define a command, this is the kind of lock you must
set. See the default command set for lots of examples. If a character/account don’t pass the
lock type the command will not even appear in their
cmd: not perm(no_tell)
“Permissions” can also be used to block users or implement highly specific bans. The above example
would be be added as a lock string to the
tell command. This will allow everyone not having the
no_tell to use the
tell command. You could easily give an account the “permission”
no_tell to disable their use of this particular command henceforth.
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dbref = caller.id lockstring = "control:id(%s);examine:perm(Builders);delete:id(%s) or perm(Admin);get:all()" % (dbref, dbref) new_obj.locks.add(lockstring)
This is how the
create command sets up new objects. In sequence, this permission string sets the
owner of this object be the creator (the one running
create). Builders may examine the object
whereas only Admins and the creator may delete it. Everyone can pick it up.
A complete example of setting locks on an object¶
Assume we have two objects - one is ourselves (not superuser) and the other is an Object
> create/drop box > desc box = "This is a very big and heavy box."
We want to limit which objects can pick up this heavy box. Let’s say that to do that we require the would-be lifter to to have an attribute strength on themselves, with a value greater than 50. We assign it to ourselves to begin with.
> set self/strength = 45
Ok, so for testing we made ourselves strong, but not strong enough. Now we need to look at what
happens when someone tries to pick up the the box - they use the
get command (in the default set).
This is defined in
evennia/commands/default/general.py. In its code we find this snippet:
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if not obj.access(caller, 'get'): if obj.db.get_err_msg: caller.msg(obj.db.get_err_msg) else: caller.msg("You can't get that.") return
get command looks for a lock with the type get (not so surprising). It also looks for an
Attribute on the checked object called get_err_msg in order to return a customized
error message. Sounds good! Let’s start by setting that on the box:
> set box/get_err_msg = You are not strong enough to lift this box.
Next we need to craft a Lock of type get on our box. We want it to only be passed if the accessing
object has the attribute strength of the right value. For this we would need to create a lock
function that checks if attributes have a value greater than a given value. Luckily there is already
such a one included in evennia (see
So the lock string will look like this:
get:attr_gt(strength, 50). We put this on the box now:
lock box = get:attr_gt(strength, 50)
get the object and you should get the message that we are not strong enough. Increase your
strength above 50 however and you’ll pick it up no problem. Done! A very heavy box!
If you wanted to set this up in python code, it would look something like this:
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from evennia import create_object # create, then set the lock box = create_object(None, key="box") box.locks.add("get:attr_gt(strength, 50)") # or we can assign locks in one go right away box = create_object(None, key="box", locks="get:attr_gt(strength, 50)") # set the attributes box.db.desc = "This is a very big and heavy box." box.db.get_err_msg = "You are not strong enough to lift this box." # one heavy box, ready to withstand all but the strongest...
On Django’s permission system¶
Django also implements a comprehensive permission/security system of its own. The reason we don’t
use that is because it is app-centric (app in the Django sense). Its permission strings are of the
appname.permstring and it automatically adds three of them for each database model in the app
for the app evennia/object this would be for example ‘object.create’, ‘object.admin’ and ‘object.edit’. This makes a lot of sense for a web application, not so much for a MUD, especially when we try to hide away as much of the underlying architecture as possible.
The django permissions are not completely gone however. We use it for validating passwords during login. It is also used exclusively for managing Evennia’s web-based admin site, which is a graphical front-end for the database of Evennia. You edit and assign such permissions directly from the web interface. It’s stand-alone from the permissions described above.