1. Code Structure and Utilities

In this lesson, we will set up the file structure for EvAdventure. We will make some utilities that will be useful later. We will also learn how to write tests.

1.1. Folder Structure

This layout is for the tutorial!

We make the evadventure folder stand-alone for the sake of the tutorial only. Leaving the code isolated in this way makes it clear what we have changed — and for you to grab what you want later. It also makes it easier to refer to the matching code in evennia/contrib/tutorials/evadventure.

For your own game, you are instead encouraged to modify your game dir in-place (i.e, directly add to commands/commands.py and modify the typeclasses/ modules directly). Except for the server/ folder, you are, in fact, free to structure your game dir code pretty much as you like.

Create a new folder named evadventure under your mygame folder. Inside it the new folder, create another folder named tests/. Make sure to put empty __init__.py files in both new folders. Doing so turns both new folders into packages from which Python understands to import automatically.

mygame/
   commands/
   evadventure/         <---
      __init__.py       <---
      tests/            <---
          __init__.py   <---
   __init__.py
   README.md
   server/
   typeclasses/
   web/
   world/

Importing anything from inside this folder from anywhere else under mygame will be done by

# from anywhere in mygame/
from evadventure.yourmodulename import whatever

This is the ‘absolute path` type of import.

Between two modules both in evadventure/, you can use a ‘relative’ import with .:

# from a module inside mygame/evadventure
from .yourmodulename import whatever

From e.g. inside mygame/evadventure/tests/ you can import from one level above using ..:

# from mygame/evadventure/tests/
from ..yourmodulename import whatever

1.2. Enums

A full example of the enum module is found in evennia/contrib/tutorials/evadventure/enums.py.

Create a new file mygame/evadventure/enums.py.

An enum (enumeration) is a way to establish constants in Python. For example:

# in a file mygame/evadventure/enums.py

from enum import Enum

class Ability(Enum):

    STR = "strength"

You can then access an enum like this:

# from another module in mygame/evadventure

from .enums import Ability

Ability.STR   # the enum itself
Ability.STR.value  # this is the string "strength"

Using enums is a recommended practice. With enums set up, we can make sure to refer to the same constant or variable every time. Keeping all enums in one place also means we have a good overview of the constants with which we are dealing.

The alternative to enums would be, for example, to pass around a string named "constitution". If you mis-spelled this as, say, "consitution", you would not necessarily know it right away because the error would happen later when the string is not recognized. By using the enum practice,should you make a typo getting Ability.COM instead of Ability.CON, Python will immediately raise an error becase this enum with the typo will not be recognized.

With enums, you can also do nice direct comparisons like if ability is Ability.WIS: <do stuff>.

Note that the Ability.STR enum does not have the actual value of, for instance, your Strength. Ability.STR is just a fixed label for the Strength ability.

Below is the enum.py module needed for Knave. It covers the basic aspects of the rule system we need to track. (Check out the Knave rules.) Should you later use another rule system, you’ll likely expand on your enums gradually as you figure out what you’ll need.

# mygame/evadventure/enums.py

class Ability(Enum):
    """
    The six base ability-bonuses and other
    abilities

    """

    STR = "strength"
    DEX = "dexterity"
    CON = "constitution"
    INT = "intelligence"
    WIS = "wisdom"
    CHA = "charisma"

    ARMOR = "armor"

    CRITICAL_FAILURE = "critical_failure"
    CRITICAL_SUCCESS = "critical_success"

    ALLEGIANCE_HOSTILE = "hostile"
    ALLEGIANCE_NEUTRAL = "neutral"
    ALLEGIANCE_FRIENDLY = "friendly"


ABILITY_REVERSE_MAP =  {
    "str": Ability.STR,
    "dex": Ability.DEX,
    "con": Ability.CON,
    "int": Ability.INT,
    "wis": Ability.WIS,
    "cha": Ability.CHA
}

Above, the Ability class holds some basic properties of a character sheet.

The ABILITY_REVERSE_MAP is a convenient map to go the other way &mdas; if in some command we were to enter the string ‘cha’, we could use this mapping to directly convert your input to the correct Ability. For example:

ability = ABILITY_REVERSE_MAP.get(your_input)

1.3. Utility Module

Create a new module mygame/evadventure/utils.py

An example of the utility module is found in evennia/contrib/tutorials/evadventure/utils.py

The utility module is used to contain general functions we may need to call repeatedly from various other modules. In this tutorial example, we only crate one utility: a function that produces a pretty display of any object we pass to it.

Below is an example of the string we want to see:

Chipped Sword
Value: ~10 coins [wielded in Weapon hand]

A simple sword used by mercenaries all over
the world.

Slots: 1, Used from: weapon hand
Quality: 3, Uses: None
Attacks using strength against armor.
Damage roll: 1d6

And, here’s the start of how the function might look:

# in mygame/evadventure/utils.py

_OBJ_STATS = """
|c{key}|n
Value: ~|y{value}|n coins{carried}

{desc}

Slots: |w{size}|n, Used from: |w{use_slot_name}|n
Quality: |w{quality}|n, Uses: |w{uses}|n
Attacks using |w{attack_type_name}|n against |w{defense_type_name}|n
Damage roll: |w{damage_roll}|n
""".strip()


def get_obj_stats(obj, owner=None):
    """
    Get a string of stats about the object.

    Args:
        obj (Object): The object to get stats for.
        owner (Object): The one currently owning/carrying `obj`, if any. Can be
            used to show e.g. where they are wielding it.
    Returns:
        str: A nice info string to display about the object.

    """
    return _OBJ_STATS.format(
        key=obj.key,
        value=10,
        carried="[Not carried]",
        desc=obj.db.desc,
        size=1,
        quality=3,
        uses="infinite",
        use_slot_name="backpack",
        attack_type_name="strength",
        defense_type_name="armor",
        damage_roll="1d6"
    )

In our new get_obj_stats function above, we set up a string template with place holders for where every element of stats information should go. Study this string so that you understand what it does. The |c, |y, |w and |n markers are Evennia color markup for making the text cyan, yellow, white and neutral-color, respectively.

Some stats elements are easy to identify in the above code. For instance, obj.key is the name of an object and obj.db.desc will hold an object’s description — this is also how default Evennia works.

So far, here in our tutorial, we have not yet established how to get any of the other properties like size or attack_type. For our current purposes, we will just set them to dummy values and we’ll need to revisit them later when we have more code in place!

1.4. Testing

Evennia comes with extensive functionality to help you test your code. A unit test allows you to set up automated testing of code. Once you’ve written your test, you can then run it over and over again to ensure later changes to your code didn’t break things by introducing errors.

create a new module mygame/evadventure/tests/test_utils.py

How would you know if you made a typo in the code above? You can manually test it by reloading your Evennia server and issuing the following in-game python command:

py from evadventure.utils import get_obj_stats;print(get_obj_stats(self))

Doing so should spit back a nice bit of string ouput about yourself! If that works, great! But, you’ll need to remember re-running that test manually when you later change the code.

In evennia/contrib/tutorials/evadventure/tests/test_utils.py is an example of the testing module. To dive deeper into unit testing in Evennia, see the Unit testing documentation.

In our particular case of this tutorial, we should expect to need to later update the test when the get_obj_stats code becomes more complete and returns more pertinent data.

Here’s a module for testing get_obj_stats.

# mygame/evadventure/tests/test_utils.py

from evennia.utils import create
from evennia.utils.test_resources import EvenniaTest

from ..import utils

class TestUtils(EvenniaTest):
    def test_get_obj_stats(self):
        # make a simple object to test with
        obj = create.create_object(
            key="testobj",
            attributes=(("desc", "A test object"),)
        )
        # run it through the function
        result = utils.get_obj_stats(obj)
        # check that the result is what we expected
        self.assertEqual(
            result,
            """
|ctestobj|n
Value: ~|y10|n coins[not carried]

A test object

Slots: |w1|n, Used from: |wbackpack|n
Quality: |w3|n, Uses: |winfinite|n
Attacks using |wstrength|n against |warmor|n
Damage roll: |w1d6|n
""".strip()
)

What happens in the above code is that we create a new test-class named TestUtils that inherits from EvenniaTest. It is this inheritance that makes this a testing class.

Important

It’s useful for any game dev to know how to test their code effectively. So, we’ll try to include a Testing section at the end of each implementation lesson that follows in this tutorial.

Writing tests for your code is optional, but highly recommended. Initially, unit testing may feel a little cumbersome or time-consuming… but you’ll thank yourself later.

We can have any number of methods called on this class. To have Evennia automatically recognize a method as one containing code to test, its name must start with the test_ prefix. We have one here as test_get_obj_stats.

In our test_get_obj_stats method, we create a dummy obj and assign it a key “testobj”. Note that we add thedesc Attribute directly in the create_object call by specifying the attribute as a tuple (name, value)!

Then, we can get the result of passing this dummy-object through the get_obj_stats function that we imported earlier.

The assertEqual method is available on all testing classes and checks that the result is equal to the string we specify. If they are the same, the test passes. Otherwise, it fails and we need to investigate what went wrong.

1.4.1. Running your Test

To run our utility module test, we need to issue the following command directly from the mygame folder:

evennia test --settings settings.py evadventure.tests

The above command will run all evadventure tests found in the mygame/evadventure/tests folder. To run only our utility tests we might instead specify the test individually:

evennia test --settings settings.py evadventure.tests.test_utils

If all goes well, the above utility test should produce output ending with OK to indicate our code has passed the test.

However, if our return string doesn’t quite match what we expected, the test will fail. We will then need to begin examining and troubleshooting our failing code.

Hint: The above example unit test code contains a deliberate error in capitalization. See if you can examine the output to interpret the deliberate error, and then fix it!

1.5. Summary

It’s very important to understand how you import code among modules in Python. If importing from Python modules is still confusing to you, it’s worth it to read more on the topic.

That said, many newcomers are confused with how to tackle these concepts. In this lesson, by creating the folder structure, two small modules and even making our first unit test, you are off to a great start!