Help with matrix 3d xarray and ObjectProperty

[Walmir Paiva]

Hello,

I would like help for a problem I am facing.
I'm building an application that uses a matrix-based 3d xarray data model (http://xarray.pydata.org/en/stable/index.html).

I would like to preserve the data in an ObjectProperty, to get the bind functionality, but apparently this property is not working with this object type.

Example code:

# -*- coding: utf-8 -*-

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import  ObjectProperty
from kivy.lang import Builder
from kivy.clock import mainthread

import pandas as pd
import numpy as np
import xarray as xr

Builder.load_string('''
<RootWidget>:
    Button:
        text: 'click to update/print current xarray dataset'
        on_press: root.change_data()
    Button:
        text: 'click to print objectproperty'
        on_press: root.print_object()

''')


class RootWidget(BoxLayout):
    xarray_obj = ObjectProperty(allownone=True)
   
    def __init__(self, **kwargs):
        super(RootWidget, self).__init__(**kwargs)
       
        self.create_dataset_base()
        self.bind(xarray_obj=self.print_xarray_obj)
   
    def create_dataset_base(self):
        #creates a dataset like a 3d array (x: price column, y: products id, z: stores), with empty database
        store = ['Walmart', 'Dia']
        list_id= ['id_1', 'id_2', 'id_3', 'id_4' ]
        price = ['unit_price']
        temp_3d_array = np.empty((len(store), len(list_id), len(price)))
       
        #object xarray
        self.ds_base = xr.Dataset({'store_price':(['stores', 'ids',  'prices'], temp_3d_array)},
            coords={'ids':list_id, 'stores': store, 'prices': price})
   
        #fill dataset  
        df_Walmart_price = pd.DataFrame({
            'price':[10.0, 20.0, 30.0, 40.0]
            }, index = ['id_1', 'id_2', 'id_3', 'id_4' ])
         
        df_Dia_price = pd.DataFrame({
            'price':[12.50, 18.75,  32.43, 37.0]
            }, index = ['id_1', 'id_2', 'id_3', 'id_4' ])
       
        self.ds_base['store_price'].loc[dict(stores= 'Walmart')] = df_Walmart_price
        self.ds_base['store_price'].loc[dict(stores= 'Dia')] = df_Dia_price
       
        #assigns dataset base to objectproperty
        self.xarray_obj = self.ds_base
        #self.xarray_obj = 'testestestestest'  # to test other object type - works correctly
       
        print(self.ds_base.store_price)   #  to confirm dataset
       
        print('type object xarray - ', type(self.ds_base))
        print('id object xarray - ', id(self.ds_base))
       
        print('type objectproperty - ', type(self.xarray_obj))
        print('id objectproperty - ', id(self.xarray_obj))
        print(self.xarray_obj)
   
    def change_data(self):
        #creates new dataset after manipulating data
        new_dataset = self.ds_base.copy(deep=True)
       
        #to transform into pandas dataframe for calculation
        df_temp = self.ds_base['store_price'].loc[dict(stores= 'Walmart')].to_pandas()
        df_temp['unit_price'] = df_temp['unit_price']*2 #doubling the value of the price column
       
        #assigns dataframe to dataset
        new_dataset['store_price'].loc[dict(stores= 'Walmart')] = df_temp
       
        #assigns dataset base to objectproperty
        self.xarray_obj = new_dataset
        #self.xarray_obj = 'foofoofoofoofoo'  #to test other object type - works correctly
       
        print(new_dataset.store_price) #to confirm calculation
       
        print(type(new_dataset))
        print(id(new_dataset))    
       
        print(id(self.xarray_obj))
        print(self.xarray_obj)

    @mainthread
    def print_xarray_obj(self, *args):
        #bind test
        print('ok - changed')
        print(args)
   
    def print_object(self):
        print(self.xarray_obj)


class TestApp(App):
    def build(self):
        return RootWidget()


TestApp().run()

If you can show me what I'm doing wrong, I appreciate it.

Thanks

[ZenCODE]

Try

    def on_xarray_obj(self, widget, value):

        print("This fires")

[Walmir Paiva]

Thanks for the reply ZenCode, but it did not work.It does not recognize the object change.

Walmir

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[ZenCODE]

Bizarre. It's not firing because xarray_obj stays None, even after you re-assign it with

    self.xarray_obj = self.ds_base

self.ds_base is a dataset, but for some very weird reason, the assignment does nothing! As you say in your code, assigning other objects works. There must be some black magic around xarray, or something in the kivy ObjectProperty that prevents assignment. I will try looking into that more closely...

[Gabriel Pettier]

You certainly want to look at how ListProperty works, and apply the same
kind of logic, that is, wrapping the object into another one (as
ObservableList is used by ListProperty), that overrides the basic
operation to dispatch changes.

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[Walmir Paiva]

Tanks tshirtman for the sugestion, but Listproperty does something even more bizarre, just save the string with the name of the variable (dictionary key).

Black magic... :)

After a few attempts,using ObjectProperty, I got into that ugly hack that worked:

        temp_list = []
        temp_list.append(new_dataset)
        #assigns dataset to objectproperty
        self.xarray_obj = None
        self.xarray_obj = temp_list

Adds a bit of complexity ... but it's what we have for the moment.

Thanks

Walmir

[Gabriel Pettier]

yes, that's a hack ^^, if it works for you, good enough, but if you
wanted a transparent management on edit, you need to create a new
property type, using the same kind of logic as ListProperty and
ObservableList, not using them directly, just taking inspiration.

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[Walmir Paiva]

In fact it is generating more complexity than I thought.
In the example worked, but in the real case it is not working properly. I still can not understand it yet.
I would very much like to follow your suggestion and try to create a new property type, but I think maybe my knowledge of python and kivy is not enough.

If you can tell me where to find some example or guide me, I would greatly appreciate it.

[Walmir Paiva]

Another hack that works in the real case:

        #assigns dataset to objectproperty
        temp_dict = {}
        temp_dict['ds'] =new_dataset
        self.xarray_obj = temp_dict

Walmir