Python function not changing variable's value, but works with renpy functions

[Kaira]

I'm working on an inventory system for my game, but for some reason one of the values isn't changing within the function :/ Hopefully someone can help me out o.o'

The objects/variables are created just before the start label:

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default inventory = []
default selected_item = None

The current function's purpose is to discard an item from the player's inventory. The button call looks like this:

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textbutton "Discard" action Function(discardItem,inventory,selected_item)
#textbutton "Discard" action [RemoveFromSet(inventory,selected_item), SetVariable("selected_item",None)]

The commented out section is the previous version of the button which works, but some buttons require some more complex actions so I would like to keep the actions to the functions.

And the function itself is in a python init and looks like this:

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    def discardItem(inventory,selected_item):
        inventory.remove(selected_item)
        selected_item = None

Doing this removes the item from the inventory, but it doesn't change the value of "selected_item" to "None"

I'm not sure if this is something specific to python, which I think it could be from what I've been reading on it, but why does renpy's function work then? And is there some way I could call that function from my python code?

I already tried this (in the python function) and it didn't work, selected_item was still set to the discarded item.

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        SetVariable("selected_item",None)

The actual screen looks like this currently (before any items are selected). The screen is a work in progress >.> (this is just the prototype)

Item selected

And this is what it looks like when the item is discarded/deleted from inventory.

However, "Current Item" section should say "None" like the first image, but it doesn't since selected_item wasn't reset. Which means if the player attempts to discard the item (which no longer exists in inventory) the game will crash.

[DannX]

In the function code as you have it, the last line is creating a local variable and setting it to None. If you want to modify an external variable (declared with default) you must use global statement:

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default selected_item = None #default declaration

init python:

    def discardItem(inventory):
        global selected_item #this tells python to use the defaulted variable instead of creating a local one
        inventory.remove(selected_item)
        selected_item = None #Now set the global variable to None

Be careful with argument and variable names, they can't be the same.

EDIT: Whoops. I forgot to edit my own code

[Kaira]

In the function code as you have it, the last line is creating a local variable and setting it to None. If you want to modify an external variable (declared with default) you must use global statement:

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default selected_item = None #default declaration

init python:

    def discardItem(inventory,selected_item):
        global selected_item #this tells python to use the defaulted variable instead of creating a local one
        inventory.remove(selected_item) #remove from the list the argument you passed to the function
        selected_item = None #Now set the global variable to None

Be careful with argument and variable names, it often leads to this kind of problems.

That sort of works, but only if I don't set "selected_item" as one of the arguments passed in the discardItem function. If I use the way you wrote it returns an error:

Parsing the script failed.
File "game/script.rpy", line 34: name 'selected_item' is local and global.

The function does work though if I do this:

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init python:

    def discardItem(inventory):
        global selected_item
        inventory.remove(selected_item)
        selected_item = None

...so it's okay to use global in this instance? I know usually you should avoid using global variables, but it seems like for this it's okay. Or that it's not really a global variable, but the command tells it access a variable from a higher scope?? Anyways, it works xD

Main main bit of programming experience comes from C++ so Python is still a bit weird to me. '___'

Thanks for the help.

[DannX]

Oops, sorry, that's why I wrote that last line about being careful with the arguments as they cannot be the same as the variable you're accessing, and I forgot to edit my code.