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More updates to the starting tutorial

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17
docs/source/Howto/Starting/Building-Quickstart.md
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@ -83,6 +83,15 @@ This created a new 'box' (of the default object type) in your inventory. Use the
name box = very large box;box;very;crate
```warning:: MUD clients and semi-colon
Some traditional MUD clients use the semi-colon `;` to separate client inputs. If so,
the above line will give an error. You need to change your client to use another command-separator
or to put it in 'verbatim' mode. If you still have trouble, use the Evennia web client instead.
```
We now renamed the box to _very large box_ (and this is what we will see when looking at it), but we
will also recognize it by any of the other names we give - like _crate_ or simply _box_ as before.
We could have given these aliases directly after the name in the `create` command, this is true for
@ -297,13 +306,11 @@ the history of your game world:
sethelp/add History = At the dawn of time ...
Next we will take a little detour to look at the _Tutorial World_. This is a little solo adventure
that comes with Evennia, a showcase for some of the things that are possible.
You will now find your new `History` entry in the `help` list and read your help-text with `help History`.
## Adding a World
After this brief introduction to building you may be ready to see a more fleshed-out example.
Evennia comes with a tutorial world for you to explore. We will try that out in the next section.
After this brief introduction to building and using in-game commands you may be ready to see a more fleshed-out
example. Evennia comes with a tutorial world for you to explore. We will try that out in the next section.
[prev lesson](Starting-Part1) | [next lesson](Tutorial-World-Introduction)

2
docs/source/Howto/Starting/Coding-Introduction.md
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@ -99,4 +99,4 @@ chat](http://webchat.freenode.net/?channels=evennia) are also there for you.
And finally, of course, have fun!
[feature-request]: (https://github.com/evennia/evennia/issues/new?title=Feature+Request%3a+%3Cdescriptive+title+here%3E&body=%23%23%23%23+Description+of+the+suggested+feature+and+how+it+is+supposed+to+work+for+the+admin%2fend+user%3a%0D%0A%0D%0A%0D%0A%23%23%23%23+A+list+of+arguments+for+why+you+think+this+new+feature+should+be+included+in+Evennia%3a%0D%0A%0D%0A1.%0D%0A2.%0D%0A%0D%0A%23%23%23%23+Extra+information%2c+such+as+requirements+or+ideas+on+implementation%3a%0D%0A%0D%0A
[bug]: https://github.com/evennia/evennia/issues/new?title=Bug%3a+%3Cdescriptive+title+here%3E&body=%23%23%23%23+Steps+to+reproduce+the+issue%3a%0D%0A%0D%0A1.+%0D%0A2.+%0D%0A3.+%0D%0A%0D%0A%23%23%23%23+What+I+expect+to+see+and+what+I+actually+see+%28tracebacks%2c+error+messages+etc%29%3a%0D%0A%0D%0A%0D%0A%0D%0A%23%23%23%23+Extra+information%2c+such+as+Evennia+revision%2frepo%2fbranch%2c+operating+system+and+ideas+for+how+to+solve%3a%0D%0A%0D%0A
[bug](https://github.com/evennia/evennia/issues/new?title=Bug%3a+%3Cdescriptive+title+here%3E&body=%23%23%23%23+Steps+to+reproduce+the+issue%3a%0D%0A%0D%0A1.+%0D%0A2.+%0D%0A3.+%0D%0A%0D%0A%23%23%23%23+What+I+expect+to+see+and+what+I+actually+see+%28tracebacks%2c+error+messages+etc%29%3a%0D%0A%0D%0A%0D%0A%0D%0A%23%23%23%23+Extra+information%2c+such+as+Evennia+revision%2frepo%2fbranch%2c+operating+system+and+ideas+for+how+to+solve%3a%0D%0A%0D%0A)

576
docs/source/Howto/Starting/Python-basic-introduction.md
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@ -29,7 +29,7 @@ game. This is useful for quick testing. From the game's input line, enter the fo
```sidebar:: Command input
The lines with a `>` indicate input to enter in-game, while the lines below are the
The line with `>` indicates input to enter in-game, while the lines below are the
expected return from that input.
```
@ -41,51 +41,140 @@ You will see
To understand what is going on: some extra info: The `print(...)` *function* is the basic, in-built
way to output text in Python. We are sending "Hello World" as an _argument_ to this function. The quotes `"..."`
mean that you are inputting a *string* (i.e. text). You could also have used single-quotes `'...'`,
Python accepts both.
Python accepts both. A third variant is triple-quotes (`"""..."""` or `'''...'''`, which work across multiple
lines and are common for larger text-blocks. The way we use the `py` command right now only supports
single-line input however.
The `print` command is a standard Python structure. We can use that here in the `py` command since
we can se the output. It's great for debugging and quick testing. But if you need to send a text
to an actual player, `print` won't do, because it doesn't know _who_ to send to. Try this:
### Making some text 'graphics'
> py me.msg("Hello world!")
Hello world!
When making a text-game you will, unsurprisingly, be working a lot with text. Even if you have the occational
button or even graphical element, the normal process is for the user to input commands as
text and get text back. As we saw above, a piece of text is called a _string_ in Python and is enclosed in
either single- or double-quotes.
This looks the same as the `print` result, but we are now actually messaging a specific *object*,
`me`. The `me` is a shortcut to 'us', the one running the `py` command. It is not some special
Python thing, but something Evennia just makes available in the `py` command for convenience
(`self` is an alias).
Strings can be added together:
The `me` is an example of an *Object instance*. Objects are fundamental in Python and Evennia.
The `me` object also contains a lot of useful resources for doing
things with that object. We access those resources with '`.`'.
> py print("This is a " + "breaking change.")
This is a breaking change.
One such resource is `msg`, which works like `print` except it sends the text to the object it
is attached to. So if we, for example, had an object `you`, doing `you.msg(...)` would send a message
to the object `you`.
A string multiplied with a number will repeat that string as many times:
> py print("|" + "-" * 40 + "|")
|----------------------------------------|
or
> py print("A" + "a" * 5 + "rgh!")
Aaaaaargh!
While combining different strings is useful, even more powerful is the ability to modify the contents
of the string in-place. There are several ways to do this in Python and we'll show two of them here. The first
is to use the `.format` _method_ of the string:
```sidebar:: Functions and Methods
Function:
Stand-alone in a python module, like `print()`
Something that performs and action when you `call` it with zero or more `arguments`. A function
is stand-alone in a python module, like `print()`
Method:
Something that sits "on" an object, like `.msg()`
A function that sits "on" an object, like `<string>.format()`.
```
For now, `print` and `me.msg` behaves the same, just remember that `print` is mainly used for
debugging and `.msg()` will be more useful for you in the future.
A method can be thought of as a resource "on" another object. The method knows on which object it
sits and can thus affect it in various ways. You access it with the period `.`. In this case, the
string has a resource `format(...)` that modifies it. More specifically, it replaced the `{}` marker
inside the string with the value passed to the format. You can do so many times:
For fun, try printing other things. Also try this:
> py self.msg("|rThis is red text!")
> py print("This is a {} idea!".format("bad"))
This is a bad idea!
or
> py print("This is the {} and {} {} idea!".format("first", "second", "great"))
This is the first and second great idea!
Adding that `|r` at the start will turn our output red. Enter the command `color ansi` or `color xterm`
to see which colors are available.
> Note the double-parenthesis at the end - the first closes the `format(...` method and the outermost
closes the `print(...`. Not closing them will give you a scary `SyntaxError`. We will talk a
little more about errors in the next section, for now just fix until it prints as expected.
Here we passed three comma-separated strings as _arguments_ to the string's `format` method. These
replaced the `{}` markers in the same order as they were given.
The input does not have to be strings either:
> py print("STR: {}, DEX: {}, INT: {}".format(12, 14, 8))
STR: 12, DEX: 14, INT: 8
To separate two Python instructions on the same line, you use the semi-colon, `;`. Try this:
> py a = "awesome sauce" ; print("This is {}!".format(a))
This is awesome sauce!
```warning:: MUD clients and semi-colon
Some MUD clients use the semi-colon `;` to split client-inputs
into separate sends. If so, the above will give an error. Most clients allow you to
run in 'verbatim' mode or to remap to use some other separator than `;`. If you still have
trouble, just use the Evennia web client for now. In real Python code you'll pretty much never use
the semi-colon.
```
What happened here was that we _assigned_ the string `"awesome sauce"` to a _variable_ we chose
to name `a`. In the next statement, Python remembered what `a` was and we passed that into `format()`
to get the output. If you replaced the value of `a` with something else in between, _that_ would be printed
instead.
Here's the stat-example again, moving the stats to variables (here we just set them, but in a real
game they may be changed over time, or modified by circumstance):
> py str, dex, int = 13, 14, 8 ; print("STR: {}, DEX: {}, INT: {}".format(stren, dex, int))
STR: 13, DEX: 14, INT: 8
The point is that even if the values of the stats change, the print() statement would not change - it just keeps
pretty-printing whatever is given to it.
Using `.format()` is convenient (and there is a [lot more](https://www.w3schools.com/python/ref_string_format.asp)
you can do with it). But the _f-string_ can be even more convenient. An
f-string looks like a normal string ... except there is an `f` front of it, like this:
f"this is now an f-string."
An f-string on its own is just like any other string. But let's redo the example we did before, using an f-string:
> py a = "awesome sauce" ; print(f"This is {a}!")
This is awesome sauce!
We could just insert that `a` variable directly into the f-string using `{a}`. Fewer parentheses to
remember and arguable easier to read as well.
> py str, dex, int = 13, 14, 8 ; print(f"STR: {str}, DEX: {dex}, INT: {int}")
STR: 13, DEX: 14, INT: 8
We will be exploring more complex string concepts when we get to creating Commands and need to
parse and understand player input.
Python itself knows nothing about colored text, this is an Evennia thing. Evennia supports the
standard color schemes of traditional MUDs.
> py print("|rThis is red text!|n This is normal color.")
Adding that `|r` at the start will turn our output bright red. `|R` will make it dark red. `|n`
gives the normal text color. You can also use RGB (Red-Green-Blue) values from 0-5 (Xterm256 colors):
> py print("|043This is a blue-green color.|[530|003 This is dark blue text on orange background.")
> If you don't see the expected color, your client or terminal may not support Xterm256 (or
color at all). Use the Evennia webclient.
Use the commands `color ansi` or `color xterm` to see which colors are available. Experiment!
### Importing code from other modules
As we saw in the previous section, we could use `me.msg` to access the `msg` method on `me`. This
use of the full-stop character is used to access all sorts of resources, including that in other
Python modules. If you've been following along, this is what we've referred to as the "Python path".
As we saw in the previous sections, we used `.format` to format strings and `me.msg` to access
the `msg` method on `me`. This use of the full-stop character is used to access all sorts of resources,
including that in other Python modules.
Keep your game running, then open a text editor of your choice. If your game folder is called
`mygame`, create a new text file `test.py` in the subfolder `mygame/world`. This is how the file
@ -130,16 +219,12 @@ path - Evennia handles this for us.
When you import the module, the top "level" of it will execute. In this case, it will immediately
print "Hello World".
> If you look in the folder you'll also often find new files ending with `.pyc`. These are compiled
Python binaries that Python auto-creates when running code. Just ignore them, you should never edit
those anyway.
Now try to run this a second time:
> py import world.test
You will *not* see any output this second time or any subsequent times! This is not a bug. Rather
it is because Python is being clever - it stores all imported modules and to be efficient it will
You will *not* see any output this second time or any subsequent times! This is not a bug. Rather
it is because of how Python importing works - it stores all imported modules and will
avoid importing them more than once. So your `print` will only run the first time, when the module
is first imported.
@ -159,29 +244,124 @@ not very useful.
> We'll get back to more advanced ways to import code in later tutorial sections - this is an
> important topic. But for now, let's press on and resolve this particular problem.
### Parsing Python errors
Running print only on import is not too helpful. We want to print whenever we like to!
Go back to your `test.py` file and erase the single `print` statement you had. Replace
it with this instead:
### Our first own function
We want to be able to print our hello-world message at any time, not just once after a server
reload. Change your `mygame/world/test.py` file to look like this:
```python
me.msg("Hello World!")
def hello_world():
print("Hello World!")
```
As you recall we used this with `py` earlier - it echoed "Hello World!" in-game.
Save your file and `reload` your server - this makes sure Evennia knows to re-import
it (with our new, fresh code this time).
As we are moving to multi-line Python code, there are some important things to remember:
To test it, import it using `py` as before
- Capitalization matters in Python. It must be `def` and not `DEF`, `who` is not the same as `Who`.
- Indentation matters in Python. The second line must be indented or it's not valid code. You should
also use a consistent indentation length. We *strongly* recommend that you, for your own sanity's sake,
set up your editor to always indent *4 spaces* (**not** a single tab-character) when you press the TAB key.
> py import world.test
So about that function. Line 1:
- `def` is short for "define" and defines a *function* (or a *method*, if sitting on an object).
This is a [reserved Python keyword](https://docs.python.org/2.5/ref/keywords.html); try not to use
these words anywhere else.
- A function name can not have spaces but otherwise we could have called it almost anything. We call
it `hello_world`. Evennia follows [Python's standard naming style](https://github.com/evennia/evennia/blob/master/CODING_STYLE.md#a-quick-list-of-code-style-points)
with lowercase letters and underscores. We recommend you do the same.
- The colon (`:`) at the end of line 1 indicates that the header of the function is complete.
Line 2:
- The indentation marks the beginning of the actual operating code of the function (the function's
*body*). If we wanted more lines to belong to this function those lines would all have to
start at least at this indentation level.
Now let's try this out. First `reload` your game to have it pick up
our updated Python module, then import it.
> reload
> py import world.test
Nothing happened! That is because the function in our module won't do anything just by importing it (this
is what we wanted). It will only act when we *call* it. So we need to first import the module and then access the
function within:
> py import world.test ; world.test.hello_world()
Hello world!
There is our "Hello World"! As mentioned earlier, use use semi-colon to put multiple
Python-statements on one line. Note also the previous warning about mud-clients using the `;` to their
own ends.
So what happened there? First we imported `world.test` as usual. But this time we continued and
accessed the `hello_world` function _inside_ the newly imported module.
By adding `()` to the `hello_world` function we _call_ it, that is we run the body of the function and
print our text. We can now redo this as many times as we want without having to `reload` in between:
> py import world.test ; world.test.hello_world()
Hello world!
> py import world.test ; world.test.hello_world()
Hello world!
> **Extra Credit:** As an exercise, try to pass something else into `hello_world`. Try for example
>to pass the number `5` or the string `"foo"`. You'll get errors telling you that they don't have
>the attribute `msg`. They don't care about `me` itself not being a string or a number. If you are
>familiar with other programming languages (especially C/Java) you may be tempted to start *validating*
>`who` to make sure it's of the right type before you send it. This is usually not recommended in Python.
>Python philosophy is to [handle](https://docs.python.org/2/tutorial/errors.html) the error if it happens
>rather than to add a lot of code to prevent it from happening. See [duck typing](https://en.wikipedia.org/wiki/Duck_typing)
>and the concept of _Leap before you Look_.
### Sending text to others
The `print` command is a standard Python structure. We can use that here in the `py` command since
we can se the output. It's great for debugging and quick testing. But if you need to send a text
to an actual player, `print` won't do, because it doesn't know _who_ to send to. Try this:
> py me.msg("Hello world!")
Hello world!
This looks the same as the `print` result, but we are now actually messaging a specific *object*,
`me`. The `me` is a shortcut to 'us', the one running the `py` command. It is not some special
Python thing, but something Evennia just makes available in the `py` command for convenience
(`self` is an alias).
The `me` is an example of an *Object instance*. Objects are fundamental in Python and Evennia.
The `me` object also contains a lot of useful resources for doing
things with that object. We access those resources with '`.`'.
One such resource is `msg`, which works like `print` except it sends the text to the object it
is attached to. So if we, for example, had an object `you`, doing `you.msg(...)` would send a message
to the object `you`.
For now, `print` and `me.msg` behaves the same, just remember that `print` is mainly used for
debugging and `.msg()` will be more useful for you in the future.
### Parsing Python errors
Let's try this new text-sending in the function we just created. Go back to
your `test.py` file and Replace the function with this instead:
```python
def hello_world():
me.msg("Hello World!")
```
Save your file and `reload` your server to tell Evennia to re-import new code,
then run it like before:
> py import world.test ; world.test.hello_world()
No go - this time you get an error!
```python
File "./world/test.py", line 1, in <module>
me.msg("Hello world!")
File "./world/test.py", line 2, in hello_world
me.msg("Hello World!")
NameError: name 'me' is not defined
```
@ -216,92 +396,258 @@ reserved word (as mentioned, it's just something Evennia came up with for conven
command). As far as the module is concerned `me` is an unfamiliar name, appearing out of nowhere.
Hence the `NameError`.
### Our first own function
### Passing arguments to functions
Let's see if we can resolve that `NameError` from the previous section. We know that `me` is defined
at the time we use the `py` command. We know this because if we do `py me.msg("Hello World!")`
directly in-game it works fine. What if we could *send* that `me` to the `test.py` module so it
knows what it is? One way to do this is with a *function*.
Change your `mygame/world/test.py` file to look like this:
We know that `me` exists at the point when we run the `py` command, because we can do `py me.msg("Hello World!")`
with no problem. So let's _pass_ that me along to the function so it knows what it should be.
Go back to your `test.py` and change it to this:
```python
def hello_world(who):
who.msg("Hello World!")
```
We now added an _argument_ to the function. We could have named it anything. Whatever `who` is,
we will call a method `.msg()` on it.
As we are moving to multi-line Python code, there are some important things to remember:
- Capitalization matters in Python. It must be `def` and not `DEF`, `who` is not the same as `Who`.
- Indentation matters in Python. The second line must be indented or it's not valid code. You should
also use a consistent indentation length. We *strongly* recommend that you, for your own sanity's sake,
set up your editor to always indent *4 spaces* (**not** a single tab-character) when you press the TAB key.
So about that function. Line 1:
- `def` is short for "define" and defines a *function* (or a *method*, if sitting on an object).
This is a [reserved Python keyword](https://docs.python.org/2.5/ref/keywords.html); try not to use
these words anywhere else.
- A function name can not have spaces but otherwise we could have called it almost anything. We call
it `hello_world`. Evennia follows [Python's standard naming style](https://github.com/evennia/evennia/blob/master/CODING_STYLE.md#a-quick-list-of-code-style-points)
with lowercase letters and underscores. We recommend you do the same.
- `who` is what we call the *argument* to our function. Arguments are variables _passed_ to the
function. We could have named it anything and we could also have multiple arguments separated by
commas. What `who` is depends on what we pass to this function when we *call* it later (hint: we'll
pass `me` to it).
- The colon (`:`) at the end of line 1 indicates that the header of the function is complete.
Line 2:
- The indentation marks the beginning of the actual operating code of the function (the function's
*body*). If we wanted more lines to belong to this function those lines would all have to
start at least at this indentation level.
- In the function body we take the `who` argument and treat it as we would have treated `me`
earlier- we expect it to have a `.msg` method we can use to send "Hello World" to.
Now let's try this out. First `reload` your game to have it pick up
our updated Python module when we reload.
> reload
> py import world.test
Nothing happened! That is because the function in our module won't do anything just by importing it.
It will only act when we *call* it. So we need to first import the module and then access the
function within:
As usual, `reload` the server to make sure the new code is available.
> py import world.test ; world.test.hello_world(me)
Hello world!
Hello World!
Now it worked. We _passed_ `me` to our function. It will appear inside the function renamed as `who` and
now the function works and prints as expected. Note how the `hello_world` function doesn't care _what_ you
pass into it as long as it has a `.msg()` method on it. So you could reuse this function over and over for other
suitable targets.
There is our "Hello World"! Using `;` is the way to put multiple Python-statements on one line.
### Finding others to send to
```warning:: MUD clients and semi-colon
Let's wrap up this first Python `py` crash-course by finding someone else to send to.
A common issue is that some MUD clients use the semi-colon `;` to split client-inputs
into separate sends. If so, you'll get a `NameError` above, stating that
`world` is not defined. Check so you understand why this is! Most clients allow you to
remap to use some other separator than `;`. You can use the Evennia web client if this
problem remains.
In Evennia's `contrib/` folder (`evennia/contrib/tutorial_examples/mirror.py`) is a handy little
object called the `TutorialMirror`. The mirror will echo whatever is being sent to it to
the room it is in.
On the game command-line, let's create a mirror:
> create/drop mirror:contrib.tutorial_examples.mirror.TutorialMirror
```sidebar:: Creating objects
The `create` command was first used to create boxes in the
`Building Stuff <Building-Quickstart>`_ tutorial. Note how it
uses a "python-path" to describe where to load the mirror's code from.
```
So what happened there? First we imported `world.test` as usual. But this time we continued and
accessed the `hello_world` function _inside_ the newly imported module.
A mirror should appear in your location.
We *call* the function with `me`, which becomes the `who` variable we use inside
the `hello_function` (they are be the same object). And since `me.msg` works, so does `who.msg`
inside the function.
> look mirror
The mirror shows your reflection:
This is User #1
> **Extra Credit:** As an exercise, try to pass something else into `hello_world`. Try for example
>to pass the number `5` or the string `"foo"`. You'll get errors telling you that they don't have
>the attribute `msg`. They don't care about `me` itself not being a string or a number. If you are
>familiar with other programming languages (especially C/Java) you may be tempted to start *validating*
>`who` to make sure it's of the right type before you send it. This is usually not recommended in Python.
>Python philosophy is to [handle](https://docs.python.org/2/tutorial/errors.html) the error if it happens
>rather than to add a lot of code to prevent it from happening. See [duck typing](https://en.wikipedia.org/wiki/Duck_typing)
>and the concept of _Leap before you Look_.
What you are seeing is actually your own avatar in the game, the same thing that is available as `me` in the `py`
command.
What we are aiming for now is the equivalent of `mirror.msg("Mirror Mirror on the wall")`. But the first thing that
comes to mind will not work:
> py mirror.msg("Mirror, Mirror on the wall ...")
NameError: name 'mirror' is not defined.
This is not surprising: Python knows nothing about "mirrors" or locations or anything. The `me` we've been using
is, as mentioned, just a convenient thing the Evennia devs makes available to the `py` command. They couldn't possibly
predict that you wanted to talk to mirrors.
Instead we will need to _search_ for that `mirror` object before we can send to it.
Make sure you are in the same location as the mirror and try:
> py me.search("mirror")
mirror
`me.search("name")` will, by default, search and _return_ an object with the given name found in _the same location_
as the `me` object is. If it can't find anything you'll see an error.
```sidebar:: Function returns
Whereas a function like `print` only prints its arguments, it's very common
for functions/methods to `return` a result of some kind. Think of the function
as a machine - you put something in and out comes a result you can use. In the case
of `me.search`, it will perform a database search and spit out the object it finds.
```
> py me.search("dummy")
Could not find 'dummy'.
Wanting to find things in the same location is very common, but as we continue we'll
find that Evennia provides ample tools for tagging, searching and finding things from all over your game.
Now that we know how to find the 'mirror' object, we just need to use that instead of `me`!
> py mirror = self.search("mirror") ; mirror.msg("Mirror, Mirror on the wall ...")
The mirror echoes back to you:
"Mirror, Mirror on the wall ..."
The mirror is useful for testing because its `.msg` method just echoes whatever is sent to it back to the room. More common
would be to talk to a player character, in which case the text you sent would have appeared in their game client.
This gives you some initial feeling for how to run Python and import Python modules. We also
tried to put a module in `module/world/`. Now let's look at the rest of the stuff you've got
inside that `mygame/` folder ...
### Multi-line py
So far we have use `py` in single-line mode, using `;` to separate multiple inputs. This is very convenient
when you want to do some quick testing. But you can also start a full multi-line Python interactive interpreter
inside Evennia.
> py
Evennia Interactive Python mode
Python 3.7.1 (default, Oct 22 2018, 11:21:55)
[GCC 8.2.0] on Linux
[py mode - quit() to exit]
(the details of the output will vary with your Python version and OS). You are now in python interpreter mode. It means
that _everything_ you insert from now on will become a line of Python (you can no longer look around or do other
commands).
> print("Hello World")
>>> print("Hello World")
Hello World
[py mode - quit() to exit]
Note that we didn't need to put `py` in front now. The system will also echo your input (that's the bit after
the `>>>`). For brevity in this tutorual we'll turn the echo off. First exit `py` and then start again with the
`/noecho` flag.
> quit()
Closing the Python console.
> py/noecho
Evennia Interactive Python mode
Python 3.7.1 (default, Oct 22 2018, 11:21:55)
[GCC 8.2.0] on Linux
[py mode - quit() to exit]
```sidebar:: interactive py
- Start with `py`.
- Use `py/noecho` if you don't want your input to be echoed for every line.
- All your inputs will now be interpreted as Python code.
- Exit with `quit()`.
```
We can now enter multi-line Python code:
> a = "Test"
> print(f"This is a {a}."}
This is a Test.
Let's try to define a function:
> def hello_world(who, txt):
...
> who.msg(txt)
...
>
[py mode - quit() to exit]
Some important things above:
- Definining a function with `def` means we are starting a new code block. Python works so that you mark the content
of the block with indention. So the next line must be manually indented (4 spaces is a good standard) in order
for Python to know it's part of the function body.
- We expand the `hello_world` function with another argument `txt`. This allows us to send any text, not just
"Hello World" over and over.
- To tell `py` that no more lines will be added to the function body, we end with an empty input. When
the normal prompt on how to exit returns, we know we are done.
Now we have defined a new function. Let's try it out:
> hello_world(me, "Hello world to me!")
Hello world to me!
The `me` is still available to us, so we pass that as the `who` argument, along with a little longer
string. Let's combine this with searching for the mirror.
> mirror = me.search("mirror")
> hello_world(mirror, "Mirror, Mirror on the wall ...")
The mirror echoes back to you:
"Mirror, Mirror on the wall ..."
Exit the `py` mode with
> quit()
Closing the Python console.
## Other ways to test Python code
The `py` command is very powerful for experimenting with Python in-game. It's great for quick testing.
But you are still limited to working over telnet or the webclient, interfaces that doesn't know anything
about Python per-se.
Outside the game, go to the terminal where you ran Evennia (or any terminal where the `evennia` command
is available).
- `cd` to your game dir.
- `evennia shell`
A Python shell opens. This works like `py` did inside the game, with the exception that you don't have
`me` available out of the box. If you want `me`, you need to first find yourself:
> import evennia
> me = evennia.search_object("YourChar")[0]
Here we make use of one of evennia's search functions, available by importing `evennia` directly.
We will cover more advanced searching later, but suffice to say, you put your own character name instead of
"YourChar" above.
> The `[0]` at the end is because `.search_object` returns a list of objects and we want to
get at the first of them (counting starts from 0).
Use `Ctrl-D` (`Cmd-D` on Mac) or `quit()` to exit the Python console.
### ipython
The default Python shell is quite limited and ugly. It's *highly* recommended to install `ipython` instead. This
is a much nicer, third-party Python interpreter with colors and many usability improvements.
pip install ipython
If `ipython` is installed, `evennia shell` will use it automatically.
evennia shell
...
IPython 7.4.0 -- An enhanced Interactive Python. Type '?' for help
In [1]:
You now have Tab-completion:
> import evennia
> evennia.<TAB>
That is, enter `evennia.` and then press the TAB key - you will be given a list of all the resources
available on the `evennia` object. This is great for exploring what Evennia has to offer. For example,
use your arrow keys to scroll to `search_object()` to fill it in.
> evennia.search_object?
Adding a `?` and pressing return will give you the full documentation for `.search_object`. Use `??` if you
want to see the entire source code.
As for the normal python interpreter, use `Ctrl-D`/`Cmd-D` or `quit()` to exit ipython.
```important:: Persistent code
Common for both `py` and `python`/`ipython` is that the code you write is not persistent - it will
be gone after you shut down the interpreter (but ipython will remember your input history). For making long-lasting
Python code, we need to save it in a Python module, like we did for `world/test.py`.
```
## Conclusions
This covers quite a lot of basic Python usage. We printed and formatted strings, defined our own
first function, fixed an error and even searched and talked to a mirror! Being able to access
python inside and outside of the game is an important skill for testing and debugging, but in
practice you will be writing most your code in Python modules.
To that end we also created a first new Python module in the `mygame/` game dir, then imported and used it.
Now let's look at the rest of the stuff you've got going on inside that `mygame/` folder ...
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