Ren'Py Tutorial [How-To] Variables and save compatibility...

anne O'nymous said:

All authors have to deal with the same problem, at some point of the development of their game, they have to add new variables.

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label after_load:
    python:
        try:
            come_anna
        except:
            come_anna = Task(_("Come to Anna"))
            TASK.append(come_anna)

anne O'nymous said:

It was the goal, so I'm glad to hear that it worked

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anne O'nymous said:

Well, until someone tell you about it, so thanks.

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anne O'nymous said:

You can safely delete the .rpyc file, as long as you don't rename a label in this file ;

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Return stack: [u'navigator_scripts.navigator_room_enter_helper', (u'game/scripts/repeatable_actions/cait/massage_sit/cait_massage_level_three.rpy', 1575100391, 28397), u'screen_utils.window_hide_pause']
Call location stack:[(u'game/scripts/navigation/navigator_scripts.rpy', 1575100391, 2322), (u'game/scripts/repeatable_actions/cait/massage_sit/cait_massage_level_three.rpy', 1575100391, 28396), u'screen_utils.window_hide_pause']

anne O'nymous said:

No, it's the opposite. Using the from clause will prevent you to have any problems, as long as you don't ask Ren'py to generate the said clause for you.
In fact, the from clause is here exactly for this case. It create a virtual label that Ren'py will use as return point, instead of the reference used by default.

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AmazonessKing said:

How would that reflect between saves? Is there a way to update those classes using something like after_load ?

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if not hasattr(char_class_obj, "horny"):
    char_class_obj.horny = 0

ZanithOne said:

If you just update the constructor, new attributes in older instances will remain undefined and will raise attribute exception unless you assign them manually. You can do it in after_load with something like this:

Python:

if not hasattr(char_class_obj, "horny"):
    char_class_obj.horny = 0

You don't need the hasattr check if you're only going to do that once and you are sure you won't call this ever again, but better safe than sorry, IMO.

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label after_load:
    default record = 1

AmazonessKing said:

Alright. And there's no way to add a default with after_load, right? Something like

Python:

label after_load:
    default record = 1

Because being a label, it only accepts $ which is basically define, right?

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ZanithOne said:

I'll be honest, I still don't completely understand the define/default behaviour. When I add new fields to an existing class I just use the code I posted earlier and run it on all instance of those classes. And it's just an attribute assignment at this point.

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define random_list1 = []
default random_list2 = []

label start:
    $ random_list1.append("test")
    $ random_list2.append("test")
    "Hi."
    "Save the game here. Then reload renpy through the developer console or Shift + R."
    "If you did, the random_list2 should retain the value, the other one doesn't."
    return

anne O'nymous said:

Since Ren'Py rely on pickle, there's another way to do this, more technical, but also more efficient. It rely on Python's magic methods, here the __setstate__( self, state ) one.

Basically speaking:
By default, when an object is created by pickle, therefore when a save file is loaded, the value saved are directly assigned to the object __dict__.
When the __setstate__ magic method exist, it will be called automatically by Python, in place of this direct assignation. Then, state will be a dictionary corresponding to __dict__ when the object was saved.

Therefore, the behavior by default is this one:

Python:

    class character_class(object):
        def __init__(self, name, type):
            self.name = name
            self.type = type
            self.level = 0
            self.exp = 0

        def __setstate( self, state ):
            self.__dict__ = state

This mean that you can interfere with the assigned values to add a new one:

Python:

    class character_class(object):
        def __init__(self, name, type):
            self.name = name
            self.type = type
            self.level = 0
            self.exp = 0
            self.horny = 0   # This is new.

        def __setstate( self, state ):
            #  Verify if the added attribute was part of the save.
            if not "horny" in state:
                # Add it with its default value if it wasn't the case.
                state["horny"] = 0
            # Then 'load' as usual.
            self.__dict__ = state

But you can go further than this, if by example you changed the name of an attribute:

Python:

    class character_class(object):
        def __init__(self, name, type):
            self.name = name
            self.class = type   # This is renamed
            self.level = 0
            self.exp = 0


        def __setstate( self, state ):
            #  Verify the old name is used for the attribute
            if "type" in state:
                #  Create an entry with the new name, while
                # keeping the saved value.
                state["name"] = state["type"]
                # Remove the entry with the old name.
                del state["type"]
            # Then 'load' as usual.
            self.__dict__ = state

In extreme cases, you can even do evil things, starting with this:

Python:

    class character_class(object):
        def __init__(self, name, type):
            self.name = name
            self.type = type
            self.level = 0
            self.exp = 0
            self.love = 0
            self.lust = 0

then deciding that separating battle and relationship stats is a better idea:

Python:

    class Battle_class(object):
        def __init__(self, name, type):
            self.name = name
            self.type = type
            self.level = 0
            self.exp = 0

    class Relation_class(object):
        def __init__(self, name):
            self.name = name
            self.love = 0
            self.lust = 0

    class character_class(object):
        def __init__(self):
            # You don't need this anymore

        def __setstate( self, state ):
            #  After this update, the object will be blank with no attributes.
            # If it's the case, just return.
            if not "name" in state: return

            #  Else it mean that you need to split the object.

            #  Ensure that the object exist, else create it. Not really sure
            # how /default/, /define/ and this interfere, so better safe than
            # sorry.
            #  Firstly the battle object
            if not hasattr( store, state["name"][:3] + "_battle" ):
                setattr( store, state["name"][:3] + "_battle", Battle_class( state["name"], state["type"] ) )

            # Then 'load' it
            obj = getattr( store, state["name"][:3] + "_battle" )
            obj.level = state["level"]
            obj.exp = state["exp"]

            # Do the same for the relation object.
            if not hasattr( store, state["name"][:3] + "_relation" ):
                setattr( store, state["name"][:3] + "_relation", Relation_class( state["name"] ) )

            obj = getattr( store, state["name"][:3] + "_relation" )
            obj.love = state["love"]
            obj.lust = state["lust"]

            # Then do nothing else, this object is now irrelevant, keep it blank.

Edit: A typo in the code, sorry.

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