CODEWITHSUNDEEP
pythonpython-3.x
Riley Hughes
Riley Hughes

Reputation: 1484

Scope problem, can access object attributes but can't access the object instance

I am creating a text adventure engine, the engine itself is working great but I am trying to implement custom events for game creators with callbacks. I have a main.py file that implements all of the game objects and builds the game. The problem is that I seem to be having trouble accessing the objects after I have instantiated them. have a look at this pseudo example code,

import engine

def build():
    # create new item objects
    key = engine.Item()
    door = engine.Item(a = 0)

    # set state of door
    door.locked(requirement = key)

    # CALLBACK FUNCTION
    def on_door_unlock():
        # ACCESSING THE ATTRIBUTE `a` IN `door` WORKS FINE
        door.a = 1
        # ACCESSING THE `key` OBJECT THROWS UnboundLocalError
        del key

    # assign callback to unlock event
    door.on_unlock(on_door_unlock)

build()
engine.run()

My file is obviously much larger than this but it is just as simple and this code isolates my problem. I am able to access the attributes of any object, but when I try to use del keyword on an object itself I get UnboundLocalError: local variable 'key' referenced before assignment

everything seems to be placed in order. So what is the problem? How can i write callback functions that can access instances of the objects I create?

Upvotes: 3

Views: 354

Answers (1)

jez
jez

Reputation: 15349

del key means no more or less than "remove the name key from the local scope". But this symbol has never been brought into the local scope of on_door_unlock and even if it had, removing it from there would not do anything to the scope of build.

One of many better approaches would be to create an explicitly-named registry of objects, for example as a dict called all_objects. Create the key inside it. Remove key from it by referring to it by name in your function.

ALL_OBJECTS = {}

def build():
    ALL_OBJECTS[ 'copperKey' ] = engine.Item()

    ...

    def on_door_unlock():

        del ALL_OBJECTS[ 'copperKey' ]
        ...

Upvotes: 2

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