# Parsing Command input

In this lesson we learn some basics about parsing the input of Commands. We will
also learn how to add, modify and extend Evennia's default commands.

## More advanced parsing

In the [last lesson](./Beginner-Tutorial-Adding-Commands.md) we made a `hit` Command and struck a dragon with it. You should have the code from that still around.

Let's expand our simple `hit` command to accept a little more complex input:

    hit <target> [[with] <weapon>]

That is, we want to support all of these forms

    hit target
    hit target weapon
    hit target with weapon

If you don't specify a weapon you'll use your fists. It's also nice to be able to skip "with" if
you are in a hurry. Time to modify `mygame/commands/mycommands.py` again. Let us break out the parsing a little, in a new method `parse`:


```{code-block} python
:linenos:
:emphasize-lines: 14,15,16,18,29,35,41
#...

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

    Usage:
      hit <target>

    """
    key = "hit"

    def parse(self):
        self.args = self.args.strip()
        target, *weapon = self.args.split(" with ", 1)
        if not weapon:
            target, *weapon = target.split(" ", 1)
        self.target = target.strip()
        if weapon:
            self.weapon = weapon[0].strip()
        else:
            self.weapon = ""

    def func(self):
        if not self.args:
            self.caller.msg("Who do you want to hit?")
            return
        # get the target for the hit
        target = self.caller.search(self.target)
        if not target:
            return
        # get and handle the weapon
        weapon = None
        if self.weapon:
            weapon = self.caller.search(self.weapon)
        if weapon:
            weaponstr = f"{weapon.key}"
        else:
            weaponstr = "bare fists"

        self.caller.msg(f"You hit {target.key} with {weaponstr}!")
        target.msg(f"You got hit by {self.caller.key} with {weaponstr}!")
# ...
```

The `parse` method is a special one Evennia knows to call _before_ `func`. At this time it has access to all the same on-command variables as `func` does. Using `parse` not only makes things a little easier to read, it also means you can easily let other Commands _inherit_ your parsing - if you wanted some other Command to also understand input on the form `<arg> with <arg>` you'd inherit from this class and just implement the `func` needed for that command without implementing `parse` anew.

```{sidebar} Tuples and Lists

- A `list` is written as `[a, b, c, d, ...]`. You can add and grow/shrink a list after it was first created.
- A `tuple` is written as `(a, b, c, d, ...)`. A tuple cannot be modified once it is created.

```
- **Line 14** - We do the stripping of `self.args` once and for all here. We also store the stripped version back
  into `self.args`, overwriting it. So there is no way to get back the non-stripped version from here on, which is fine
  for this command.
- **Line 15** - This makes use of the `.split` method of strings. `.split` will, well, split the string by some criterion.
    `.split(" with ", 1)` means "split the string once, around the substring `" with "` if it exists". The result
    of this split is a _list_. Just how that list looks depends on the string we are trying to split:
    1. If we entered just `hit smaug`, we'd be splitting just `"smaug"` which would give the result `["smaug"]`.
    2. `hit smaug sword` gives `["smaug sword"]`
    3. `hit smaug with sword` gives `["smaug", "sword"]`

    So we get a list of 1 or 2 elements. We assign it to two variables like this, `target, *weapon = `. That asterisk in `*weapon` is a nifty trick - it will automatically become a tuple of _0 or more_ values. It sorts of "soaks" up everything left over.
    1. `target` becomes `"smaug"` and `weapon` becomes `()` (an empty tuple)
    2. `target` becomes `"smaug sword"` and `weapon` becomes `()`
    3. `target` becomes `"smaug"` and `weapon` becomes `("sword",)` (this is a tuple with one element, the comma [is required](https://docs.python.org/3/tutorial/datastructures.html?highlight=tuple#tuples-and-sequences) to indicate this).
	
- **Lines 16-17** - In this `if` condition we check if `weapon` is falsy (that is, the empty list). This can happen
    under two conditions (from the example above):
    1. `target` is simply `smaug`
    2. `target` is `smaug sword`

    To separate these cases we split `target` once again, this time by empty space `" "`. Again we store the result back with `target, *weapon =`. The result will be one of the following:
    1. `target` remains `"smaug"` and `weapon` remains `[]`
    2. `target` becomes `"smaug"` and `weapon` becomes `("sword",)`
- **Lines 18-22** - We now store `target` and `weapon` into `self.target` and `self.weapon`. We must store on `self` in order for these local variables to become available in `func` later. Note that once we know that `weapon` exists, it must be a tuple (like `("sword",)`), so we use `weapon[0]` to get the first element of that tuple (tuples and lists in Python are indexed from 0). The instruction `weapon[0].strip()` can be read as "get the first string stored in the tuple `weapon` and remove all extra whitespace on it with `.strip()`". If we forgot the `[0]` here, we'd get an error since a tuple (unlike the string inside the tuple) does not have the `.strip()` method. 

Now onto the `func` method. The main difference is we now have `self.target` and `self.weapon` available for convenient use.
```{sidebar}
Here we create the messages to send to each side of the fight explicitly. Later we'll find out how to use Evennia's [inline functions](../../../Components/FuncParser.md) to send a single string that looks different depending on who sees it.
```

- **Lines 29 and 35** - We make use of the previously parsed search terms for the target and weapon to find the
    respective resource.
- **Lines 34-39** - Since the weapon is optional, we need to supply a default (use our fists!) if it's not set. We
    use this to create a `weaponstr` that is different depending on if we have a weapon or not.
- **Lines 41-42** - We merge the `weaponstr` with our attack texts and send it to attacker and target respectively.

Let's try it out!

    > reload
    > hit smaug with sword
    Could not find 'sword'.
    You hit smaug with bare fists!

Oops, our `self.caller.search(self.weapon)` is telling us that it found no sword. This is reasonable (we don't have a sword). Since we are not `return`ing when failing to find a weapon in the way we do if we find no `target`,  we still continue fighting with our bare hands. 

This won't do. Let's make ourselves a sword:

    > create sword

Since we didn't specify `/drop`, the sword will end up in our inventory and can seen with the `i` or `inventory` command. The `.search` helper will still find it there. There is no need to reload to see this change (no code changed, only stuff in the database).

    > hit smaug with sword
    You hit smaug with sword!

Poor Smaug.

## Adding a Command to an object

```{sidebar} Command Sets on Characters 
In case you wonder, the 'Character CmdSet' on `Characters` is configured to be available to _only_ that Character. If not, you'd get command multi-matches for things like `look` whenever you were in the same room with another character using the same command set. See [Command Sets](../../../Components/Command-Sets.md) docs for more info.
```
As we learned in the lesson about [Adding commands](./Beginner-Tutorial-Adding-Commands.md), Commands are are grouped in Command Sets. Such Command Sets are attached to an object with `obj.cmdset.add()` and will then be available for that object to use. 

What we didn't mention  before is that by default those commands are _also available to those in the same location as that object_. If you did the [Building quickstart lesson](./Beginner-Tutorial-Building-Quickstart.md) you've seen an example of this with the "Red Button" object. The [Tutorial world](./Beginner-Tutorial-Tutorial-World.md) also has many examples of objects with commands on them.

To show how this could work, let's put our 'hit' Command on our simple `sword` object from the previous section.

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

We find the sword (it's still in our inventory so `self.search` should be able to find it), then
add `MyCmdSet` to it. This actually adds both `hit` and `echo` to the sword, which is fine.

Let's try to swing it!

    > hit
    More than one match for 'hit' (please narrow target):
    hit-1 (sword #11)
    hit-2

```{sidebar} Multi-matches

Some game engines will just pick the first hit when finding more than one. Evennia will always give you a choice. The reason for this is that Evennia cannot know if `hit` and `hit` are different or the same - maybe it behaves differently depending on the object it sits on? Besides, imagine if you had a red and a blue button both with the command `push` on it. Now you just write `push`. Wouldn't you prefer to be asked _which_ button you really wanted to push?
```

Woah, that didn't go as planned. Evennia actually found _two_ `hit` commands and didn't know which one to use (_we_ know they are the same, but Evennia can't be sure of that). As we can see, `hit-1` is the one found on the sword. The other one is from adding `MyCmdSet` to ourself earlier. It's easy enough to tell Evennia which one you meant:

    > hit-1
    Who do you want to hit?
    > hit-2
    Who do you want to hit?

In this case we don't need both command-sets, we should drop the version of `hit` sitting on our ourselves.

Go to `mygame/commands/default_cmdsets.py` and find the line where you added 
`MyCmdSet` in the previous lesson. Delete or comment it out: 

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

# ...

class CharacterCmdSet(default_cmds.CharacterCmdSet):

    # ... 
    def at_object_creation(self): 

        # self.add(MyCmdSet)    # <---------

```

Next `reload` and you'll only have one `hit` command available:

    > hit
    Who do you want to hit?

Now try making a new location and then drop the sword in it.

    > tunnel n = kitchen
    > n
    > drop sword
    > s
    > hit
    Command 'hit' is not available. Maybe you meant ...
    > n
    > hit
    Who do you want to hit?

The `hit` command is only available if you hold _or_ are in the same room as the sword.

### You need to hold the sword!

```{sidebar} Locks

Evennia Locks are defined as a mini-language defined in `lockstrings`. The lockstring is on a form `<situation>:<lockfuncs>`, where `situation` determines when this lock applies and the `lockfuncs` (there can be more than one) are run to determine if the lock-check passes or not depending on circumstance.
```

Let's get a little ahead of ourselves and make it so you have to _hold_ the sword for the `hit` command to be available. This involves a [Lock](../../../Components/Locks.md). We'll cover locks in more detail later, just know that they are useful for limiting the kind of things you can do with an object, including limiting just when you can call commands on it.

    > py self.search("sword").locks.add("call:holds()")

We added a new lock to the sword. The _lockstring_ `"call:holds()"` means that you can only _call_ commands on this object if you are _holding_ the object (that is, it's in your inventory).

For locks to work, you cannot be _superuser_, since the superuser passes all locks. You need to `quell` yourself first:

```{sidebar} quell/unquell

Quelling allows you as a developer to take on the role of players with less priveleges. This is useful for testing and debugging, in particular since a superuser has a little `too` much power sometimes. Use `unquell` to get back to your normal self.
```

    > quell
	
If the sword lies on the ground, try

    > hit
    Command 'hit' is not available. ..
    > get sword
    > hit
    > Who do you want to hit?

After we've waved the sword around (hit a dragon or two), we will get rid of ours sword so we have a clean slate with no more `hit` commands floating around. We can do that in two ways:

    delete sword

or

    py self.search("sword").delete()


## Adding the Command to a default Cmdset


As we have seen we can use `obj.cmdset.add()` to add a new cmdset to objects, whether that object is ourself (`self`) or other objects like the `sword`. Doing this this way is a little cumbersome though. It would be better to add this to all characters. 

The default cmdset are defined in `mygame/commands/default_cmdsets.py`. Open that file now:

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

from evennia import default_cmds

class CharacterCmdSet(default_cmds.CharacterCmdSet):

    key = "DefaultCharacter"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #

class AccountCmdSet(default_cmds.AccountCmdSet):

    key = "DefaultAccount"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #

class UnloggedinCmdSet(default_cmds.UnloggedinCmdSet):

    key = "DefaultUnloggedin"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #

class SessionCmdSet(default_cmds.SessionCmdSet):

    key = "DefaultSession"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #
```

```{sidebar} super()

The `super()` function refers to the parent of the current class and is commonly used to call same-named methods on the parent.
```
`evennia.default_cmds` is a container that holds all of Evennia's default commands and cmdsets. In this module we can see that this was imported and then a new child class was made for each cmdset. Each class looks familiar (except the `key`, that's mainly used to easily identify the cmdset in listings). In each `at_cmdset_creation` all we do is call `super().at_cmdset_creation` which means that we call `at_cmdset_creation() on the _parent_ CmdSet.

This is what adds all the default commands to each CmdSet.

When the `DefaultCharacter` (or a child of it) is created, you'll find that the equivalence of  `self.cmdset.add("default_cmdsets.CharacterCmdSet, persistent=True")` gets called. This means that all new Characters get this cmdset. After adding more commands to it, you just need to reload to have all characters see it. 

- Characters (that is 'you' in the gameworld) has the `CharacterCmdSet`.
- Accounts (the thing that represents your out-of-character existence on the server) has the `AccountCmdSet`
- Sessions (representing one single client connection) has the `SessionCmdSet`
- Before you log in (at the connection screen) your Session have access to the `UnloggedinCmdSet`.

For now, let's add our own `hit` and `echo` commands to the `CharacterCmdSet`:


```python
# ...

from commands import mycommands

class CharacterCmdSet(default_cmds.CharacterCmdSet):

    key = "DefaultCharacter"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #
        self.add(mycommands.CmdEcho)
        self.add(mycommands.CmdHit)

```

    > reload
    > hit
    Who do you want to hit?

Your new commands are now available for all player characters in the game. There is another way to add a bunch of commands at once, and that is to add your own _CmdSet_ to the other cmdset.

```python
from commands import mycommands

class CharacterCmdSet(default_cmds.CharacterCmdSet):

    key = "DefaultCharacter"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #
        self.add(mycommands.MyCmdSet)
```

Which way you use depends on how much control you want, but if you already have a CmdSet,
this is practical. A Command can be a part of any number of different CmdSets.

### Removing Commands

To remove your custom commands again, you of course just delete the change you did to
`mygame/commands/default_cmdsets.py`. But what if you want to remove a default command?

We already know that we use `cmdset.remove()` to remove a cmdset. It turns out you can
do the same in `at_cmdset_creation`. For example, let's remove the default `get` Command
from Evennia. If you investigate the `default_cmds.CharacterCmdSet` parent, you'll find that its class is `default_cmds.CmdGet` (the 'real' location is `evennia.commands.default.general.CmdGet`). 


```python
# ...
from commands import mycommands

class CharacterCmdSet(default_cmds.CharacterCmdSet):

    key = "DefaultCharacter"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #
        self.add(mycommands.MyCmdSet)
        self.remove(default_cmds.CmdGet)
# ...
```

    > reload
    > get
    Command 'get' is not available ...

## Replace a default command

At this point you already have all the pieces for how to do this! We just need to add a new
command with the same `key` in the `CharacterCmdSet` to replace the default one.

Let's combine this with what we know about classes and how to _override_ a parent class. Open `mygame/commands/mycommands.py` and make a new `get` command: 

```{code-block} python
:linenos:
:emphasize-lines: 2,7,8,9

# up top, by the other imports
from evennia import default_cmds

# somewhere below
class MyCmdGet(default_cmds.CmdGet):

    def func(self):
        super().func()
        self.caller.msg(str(self.caller.location.contents))
```

- **Line 2**: We import `default_cmds` so we can get the parent class.
We made a new class and we make it _inherit_ `default_cmds.CmdGet`. We don't
need to set `.key` or `.parse`, that's already handled by the parent.
In `func` we call `super().func()` to let the parent do its normal thing,
- **Line 7**: By adding our own `func` we replace the one in the parent.
- **Line 8**: For this simple change we still want the command to work the
  same as before, so we use `super()` to call `func` on the parent.
- **Line 9**: `.location` is the place an object is at. `.contents` contains, well, the
    contents of an object. If you tried `py self.contents` you'd get a list that equals
    your inventory. For a room, the contents is everything in it.
    So `self.caller.location.contents` gets the contents of our current location. This is
    a _list_. In order send this to us with `.msg` we turn the list into a string. Python
    has a special function `str()` to do this.

We now just have to add this so it replaces the default `get` command. Open
`mygame/commands/default_cmdsets.py` again:

```python
# ...
from commands import mycommands

class CharacterCmdSet(default_cmds.CharacterCmdSet):

    key = "DefaultCharacter"

    def at_cmdset_creation(self):

        super().at_cmdset_creation()
        #
        # any commands you add below will overload the default ones
        #
        self.add(mycommands.MyCmdSet)
        self.add(mycommands.MyCmdGet)
# ...
```

We don't need to use `self.remove()` first; just adding a command with the same `key` (`get`) will replace the default `get` we had from before.

```{sidebar} Another way

Instead of adding `MyCmdGet` explicitly in default_cmdset.py, you could also add it to `mycommands.MyCmdSet` and let it be added automatically here for you.
```

    > reload
    > get
    Get What?
    [smaug, fluffy, YourName, ...]

We just made a new `get`-command that tells us everything we could pick up (well, we can't pick up ourselves, so there's some room for improvement there ...).

## Summary

In this lesson we got into some more advanced string formatting - many of those tricks will help you a lot in the future! We also made a functional sword. Finally we got into how to add to, extend and replace a default command on ourselves. Knowing to add commands is a big part of making a game! 

We have been beating on poor Smaug for too long. Next we'll create more things to play around with.