# Adding custom commands

In this lesson we'll learn how to create our own Evennia [Commands](../../../Components/Commands.md) If you are new to Python you'll also learn some more basics about how to manipulate strings and get information out of Evennia.

A Command is something that handles the input from a user and causes a result to happen.
An example is `look`, which examines your current location and tells you what it looks like and what is in it.

```{sidebar} Commands are not typeclassed

If you just came from the previous lesson, you might want to know that Commands and CommandSets are not `typeclassed`. That is, instances of them are not saved to the database. They are "just" normal Python classes.
```

In Evennia, a Command is a Python _class_. If you are unsure about what a class is, review the
[previous lesson about it](./Beginner-Tutorial-Python-classes-and-objects.md)! A Command inherits from `evennia.Command` or from one of the alternative command- classes, such as `MuxCommand` which is what most default commands use. 

All Commands are grouped in another class called a _Command Set_. Think of a Command Set as a bag holding many different commands. One CmdSet could for example hold all commands for combat, another for building etc. 

Command-Sets are then associated with objects, for example with your Character. Doing so makes the commands in that cmdset available to the object. By default, Evennia groups all character-commands into one big cmdset called the `CharacterCmdSet`. It sits on `DefaultCharacter` (and thus, through inheritance, on `typeclasses.characters.Character`). 

## Creating a custom command

Open `mygame/commands/command.py`. This file already has stuff filled in for you.

```python
"""
(module docstring)
"""

from evennia import Command as BaseCommand
# from evennia import default_cmds

class Command(BaseCommand):
    """
    (class docstring)
    """
    pass

# (lots of commented-out stuff)
# ...
```

Ignoring the docstrings (which you can read if you want), this is the only really active code in the module.

We can see that we import `Command` from `evennia` and use the `from ... import ... as ...` form to rename it to `BaseCommand`. This is so we can let our child class also be named `Command` to make it easier to reference.  The class itself doesn't do anything, it just has `pass`. So in the same way as `Object` and `Character` in the previous lessons, this class is identical to its parent.

> The commented out `default_cmds` gives us access to Evennia's default commands for easy overriding. We'll try that a little later.

We could modify this module directly, but let's work in a separate module just for the heck of it. Open a new file `mygame/commands/mycommands.py` and add the following code:

```python
# in mygame/commands/mycommands.py

from commands.command import Command

class CmdEcho(Command):
    key = "echo"

```

This is the simplest form of command you can imagine. It just gives itself a name, "echo". This is what you will use to call this command later.

Next we need to put this in a CmdSet. It will be a one-command CmdSet for now! Change your file as such:


```python
# in mygame/commands/mycommands.py

from commands.command import Command
from evennia import CmdSet

class CmdEcho(Command):
    key = "echo"


class MyCmdSet(CmdSet):

    def at_cmdset_creation(self):
        self.add(CmdEcho)

```

Our `MyCmdSet` class must have an `at_cmdset_creation` method, named exactly like this - this is what Evennia will be looking for when setting up the cmdset later, so if you didn't set it up, it will use the parent's version, which is empty. Inside we add the command class to the cmdset by `self.add()`. If you wanted to add more commands to this CmdSet you could just add more lines of `self.add` after this.

Finally, let's add this command to ourselves so we can try it out. In-game you can experiment with `py` again:

    > py me.cmdset.add("commands.mycommands.MyCmdSet")

The `me.cmdset` is the store of all cmdsets stored on us. By giving the path to our CmdSet class, it will be added. 

Now try

    > echo
    Command "echo" has no defined `func()`. Available properties ...
    ...(lots of stuff)...

`echo` works! You should be getting a long list of outputs. Your `echo` function is not really "doing" anything yet and the default function is then to show all useful resources available to you when you use your Command. Let's look at some of those listed:

```
Command "echo" has no defined `func()` method. Available properties on this command are:

     self.key (<class 'str'>): "echo"
     self.cmdname (<class 'str'>): "echo"
     self.raw_cmdname (<class 'str'>): "echo"
     self.raw_string (<class 'str'>): "echo
"
     self.aliases (<class 'list'>): []
     self.args (<class 'str'>): ""
     self.caller (<class 'typeclasses.characters.Character'>): YourName
     self.obj (<class 'typeclasses.characters.Character'>): YourName
     self.session (<class 'evennia.server.serversession.ServerSession'>): YourName(#1)@1:2:7:.:0:.:0:.:1
     self.locks (<class 'str'>): "cmd:all();"
     self.help_category (<class 'str'>): "general"
     self.cmdset (... a long list of commands ...)
```
These are all properties you can access with `.` on the Command instance, such as `.key`, `.args` and so on. Evennia makes these available to you and they will be different every time a command is run. The most important ones we will make use of now are:

 - `caller` - this is 'you', the person calling the command.
 - `args` - this is all arguments to the command. Now it's empty, but if you tried `echo foo bar` you'd find that this would be `" foo bar"` (including the extra space  between `echo` and `foo` that you may want to strip away).
 - `obj` - this is object on which this Command (and CmdSet) "sits". So you, in this case.
 - `raw_string` is not commonly used, but it's the completely unmodified input from the user. It even includes the line break used to send to the command to the server (that's why the end-quotes appear on the next line).

The reason our command doesn't do anything yet is because it's missing a `func` method. This is what Evennia looks for to figure out what a Command actually does. Modify your `CmdEcho` class:

```python
# in mygame/commands/mycommands.py
# ...

class CmdEcho(Command):
    """
    A simple echo command

    Usage:
        echo <something>

    """
    key = "echo"

    def func(self):
        self.caller.msg(f"Echo: '{self.args}'")

# ...
```

First we added a docstring. This is always a good thing to do in general, but for a Command class, it will also automatically become the in-game help entry! 

```{sidebar} Use Command.msg 
In a Command class, the `self.msg()` acts as a convenient shortcut for `self.caller.msg()`. Not only is it shorter, it also has some advantages because the command can include more metadata with the message. So using `self.msg()` is usually better. For this tutorial though, `self.caller.msg()` is more explicit in showing what is going on.
```

Next we add the `func` method. It has one active line where it makes use of some of those variables the Command class offers to us. If you did the [basic Python tutorial](./Beginner-Tutorial-Python-basic-introduction.md), you will recognize `.msg` - this will send a message to the object it is attached to us - in this case `self.caller`, that is, us. We grab `self.args` and includes that in the message.

Since we haven't changed `MyCmdSet`, that will work as before. Reload and re-add this command to ourselves to try out the new version:

    > reload
    > py self.cmdset.add("commands.mycommands.MyCmdSet")
    > echo
    Echo: ''

Try to pass an argument:

    > echo Woo Tang!
    Echo: ' Woo Tang!'

Note that there is an extra space before `Woo`. That is because self.args contains _everything_ after the command name, including spaces. Let's remove that extra space with a small tweak:

```python
# in mygame/commands/mycommands.py
# ...

class CmdEcho(Command):
    """
    A simple echo command

    Usage:
        echo <something>

    """
    key = "echo"

    def func(self):
        self.caller.msg(f"Echo: '{self.args.strip()}'")

# ...
```

The only difference is that we called `.strip()` on `self.args`. This is a helper method available on all strings - it strips out all whitespace before and after the string. Now the Command-argument will no longer have any space in front of it.

    > reload
    > py self.cmdset.add("commands.mycommands.MyCmdSet")
    > echo Woo Tang!
    Echo: 'Woo Tang!'

Don't forget to look at the help for the echo command:

    > help echo

You will get the docstring you put in your Command-class! 

### Making our cmdset persistent

It's getting a little annoying to have to re-add our cmdset every time we reload, right? It's simple enough to make `echo` a _persistent_ change though:

    > py self.cmdset.add("commands.mycommands.MyCmdSet", persistent=True)

Now you can `reload` as much as you want and your code changes will be available directly without needing to re-add the MyCmdSet again. 

We will add this cmdset in another way, so remove it manually: 

    > py self.cmdset.remove("commands.mycommands.MyCmdSet")

### Add the echo command to the default cmdset 

Above we added the `echo` command to ourselves. It will _only_ be available to us and noone else in the game. But all commands in Evennia are part of command-sets, including the normal `look` and `py` commands we have been using all the while. You can easily extend the default command set with your `echo` command - this way _everyone_ in the game will have access to it! 

In `mygame/commands/` you'll find an existing module named `default_cmdsets.py` Open it and you'll find four empty cmdset-classes: 

- `CharacterCmdSet` - this sits on all Characters (this is the one we usually want to modify)
- `AccountCmdSet` - this sits on all Accounts (shared between Characters, like `logout` etc)
- `UnloggedCmdSet` - commands available _before_ you login, like the commands for creating your password and connecting to the game.
- `SessionCmdSet` - commands unique to your Session (your particular client connection). This is unused by default.

Tweak this file as follows:

```python
# in mygame/commands/default_cmdsets.py 

# ... 

from . import mycommands    # <-------  

class CharacterCmdSet(default_cmds.CharacterCmdSet):
    """
    The `CharacterCmdSet` contains general in-game commands like `look`,
    `get`, etc available on in-game Character objects. It is merged with
    the `AccountCmdSet` when an Account puppets a Character.
    """
 
    key = "DefaultCharacter"
 
    def at_cmdset_creation(self):
        """
        Populates the cmdset
        """
        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones.
        #
        self.add(mycommands.CmdEcho)    # <-----------

# ... 
```

```{sidebar} super() and overriding defaults
The `super()` Python keyword means that the _parent_ is called. In this case, the parent adds all default commands to this cmdset.  

Coincidentally, this is also how you replace default commands in Evennia!jj To replace e.g. the command `get`, you just give your replacement command the `key` 'get' and add it here - since it's added after `super()`, it will replace the default version of `get`.
```
This works the same way as when you added `CmdEcho` to your `MyCmdSet`. The only difference cmdsets are automatically added to all Characters/Accounts etc so you don't have to do so manually. We must also make sure to import the `CmdEcho` from your `mycommands` module in order for this module to know about it. The period ''`.`'' in  `from . import mycommands` means that we are telling Python that `mycommands.py` sits in the same directory as this current module. We want to import the entire module. Further down we access `mycommands.CmdEcho` to add it to the character cmdset.

Just `reload` the server and your `echo` command will be available again. There is no limit to how many cmdsets a given Command can be a part of. 

To remove, you just comment out or delete the `self.add()` line. Keep it like this for now though - we'll expand on it below. 
### Figuring out who to hit

Let's try something a little more exciting than just echo. Let's make a `hit` command, for punching someone in the face! This is how we want it to work:

    > hit <target>
    You hit <target> with full force!

Not only that, we want the `<target>` to see

    You got hit by <hitter> with full force!

Here, `<hitter>` would be the one using the `hit` command and `<target>` is the one doing the punching; so if your name was `Anna`, and you hit someone named `Bob`, this would look like this: 

    > hit bob
    You hit Bob with full force!

And Bob would see

    You got hit by by Anna with full force!

Still in `mygame/commands/mycommands.py`, add a new class, between `CmdEcho` and `MyCmdSet`.

```{code-block} python
:linenos:
:emphasize-lines: 5,6,13,16,19,20,21,23
# in mygame/commands/mycommands.py

# ...

class CmdHit(Command):
    """
    Hit a target.

    Usage:
      hit <target>

    """
    key = "hit"

    def func(self):
        args = self.args.strip()
        if not args:
            self.caller.msg("Who do you want to hit?")
            return
        target = self.caller.search(args)
        if not target:
            return
        self.caller.msg(f"You hit {target.key} with full force!")
        target.msg(f"You got hit by {self.caller.key} with full force!")

# ...
```

A lot of things to dissect here:
- **Line 5**: The normal `class` header. We inherit from `Command` which we imported at the top of this file.
- **Lines 6-12**: The docstring and help-entry for the command. You could expand on this as much as you wanted.
- **Line 13**: We want to write `hit` to use this command.
- **Line 16**: We strip the whitespace from the argument like before. Since we don't want to have to do `self.args.strip()` over and over, we store the stripped version in a _local variable_ `args`. Note that we don't modify `self.args` by doing this, `self.args` will still have the whitespace and is not the same as `args` in this example.

```{sidebar} if-statements
The full form of the if statement is
	
	if condition:
	    ...
	elif othercondition:
	    ...
	else:
	    ...

There can be any number of `elifs` to mark when different branches of the code should run. If `else` is provided, it will run if none of the other conditions were truthy. 
```

- **Line 17** has our first _conditional_, an `if` statement. This is written on the form `if <condition>:` and only if that condition is 'truthy' will the indented code block under the `if` statement run. To learn what is truthy in Python it's usually easier to learn what is "falsy":
    - `False` - this is a reserved boolean word in Python. The opposite is `True`.
    - `None` - another reserved word. This represents nothing, a null-result or value.
    - `0` or `0.0`
    - The empty strings `""`, `''`, or empty triple-strings like `""""""`,  `''''''`
    - Empty _iterables_ we haven't used yet, like empty lists `[]`, empty tuples `()` and empty dicts `{}`.
    - Everything else is "truthy".

    The conditional on **Line 16**'s condition is `not args`. The `not` _inverses_ the result, so if `args` is the empty string (falsy), the whole conditional becomes truthy. Let's continue in the code:
```{sidebar} Errors in your code

With longer code snippets to try, it gets more and more likely you'll
make an error and get a `traceback` when you reload. This will either appear
directly in-game or in your log (view it with `evennia -l` in a terminal).

Don't panic - tracebacks are your friends! They are to be read bottom-up and usually describe exactly where your problem is. Refer to [The Python introduction lesson](./Beginner-Tutorial-Python-basic-introduction.md) for more hints. If you get stuck, reach out to the Evennia community for help.
```
- **Lines 16-17**: This code will only run if the `if` statement is truthy, in this case if `args` is the empty string.
- **Line 19**: `return` is a reserved Python word that exits `func` immediately.
- **Line 20**: We use `self.caller.search` to look for the target in the current location.
- **Lines 21-22**: A feature of `.search` is that it will already inform `self.caller` if it couldn't find the target. In that case, `target` will be `None` and we should just directly `return`.
- **Lines 23-24**: At this point we have a suitable target and can send our punching strings to each.

Finally we must also add this to a CmdSet. Let's add it to `MyCmdSet`.

```python
# in mygame/commands/mycommands.py

# ...
class MyCmdSet(CmdSet):

    def at_cmdset_creation(self):
        self.add(CmdEcho)
        self.add(CmdHit)

```

Note that since we did `py self.cmdset.remove("commands.mycommands.MyCmdSet")` earlier, this cmdset is no longer available on our Character. Instead we will add these commands directly to our default cmdset.

```python
# in mygame/commands/default_cmdsets.py 

# ,.. 

from . import mycommands    

class CharacterCmdSet(default_cmds.CharacterCmdSet):
    """
    The `CharacterCmdSet` contains general in-game commands like `look`,
    `get`, etc available on in-game Character objects. It is merged with
    the `AccountCmdSet` when an Account puppets a Character.
    """
 
    key = "DefaultCharacter"
 
    def at_cmdset_creation(self):
        """
        Populates the cmdset
        """
        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones.
        #
        self.add(mycommands.MyCmdSet)    # <-----------
# ... 
```

We changed from adding the individual `echo` command to adding the entire `MyCmdSet` in one go! This will add all commands in that cmdset to the `CharacterCmdSet` and is a practical way to add a lot of command in one go. Once you explore Evennia further, you'll find that [Evennia contribs](../../../Contribs/Contribs-Overview.md) all distribute their new commands in cmdsets, so you can easily add them to your game like this.

Next we reload to let Evennia know of these code changes and try it out:

    > reload
    hit
    Who do you want to hit?
    hit me
    You hit YourName with full force!
    You got hit by YourName with full force!

Lacking a target, we hit ourselves. If you have one of the dragons still around from the previous lesson you could try to hit it (if you dare):

    hit smaug
    You hit Smaug with full force!

You won't see the second string. Only Smaug sees that (and is not amused).


## Summary

In this lesson we learned how to create our own Command, add it to a CmdSet and then to ourselves. We also upset a dragon.

In the next lesson we'll learn how to hit Smaug with different weapons. We'll also
get into how we replace and extend Evennia's default Commands.
